Midterm Exam Discussion

This post is intended to give everyone an overview of the midterm exam, to highlight the areas that were done well and to indicate areas that need work.  I will also highlight questions that were similar to clicker questions used in classroom quizzes.  The information is presented in the same order that the exam was set up.

Midterm mark distribution

First of all, the overall distribution of marks is presented in Figure 1.  Although, the majority of students passed the midterm, 23 students out of 60 had marks 50% and lower and only two students out of 60 had a mark above 81%.  The class average was 58%.

Figure 1. Distribution of marks for the SLSC 240 midterm.  Percentage of students is out of 60 students and the midterm exam percent ranges are out of a total of 55 marks.

Part I. Multiple choice questions

Overall, most students did relatively well on the multiple choice section.  The average mark was 7.7 correct answers out of 10 possible marks.  There were four questions that people struggled with though, these included questions b, e, g and h.  At least 30% of the class selected the incorrect answer for these four questions.

The correct answer for b is 3 “soil forming factors are not expressed equally in all parts of the profile”.

Question e was actually a question that was previously used in a clicker quiz.  The question appeared in exact same form, but on the midterm 37% of the class selected the incorrect answer.  The correct answer for e is 3 “air filled porosity”.

The correct answer for g is 4 “the weight of soil/unit volume of soil solids”.

The correct answer for h is 1 “Aluminum Al³⁺”.

On the positive side, question c was very similar to a clicker question presented on CEC and 97% of the class got it correct.  As well, question f (pH values) was very similar to a clicker question presented in class, but the pH values had been changed slightly and 75% of the class selected the correct answer, option 5.

Did you find the multiple choice questions difficult?  Do you think the clicker quizzes prepared you for the type of questions you saw on the midterm?

Part II. Matching

Again, for the most part, the matching part of the exam was done relatively well.  On average, students got 7.1 marks out of a possible 10.  There were three terms that stood out as being difficult concepts.  Soil dispersion, negative charge, and exchangeable H+ were terms that 50% or more the class matched incorrectly.  These are all concepts associated with cation exchange capacity.  In regards to negative charge, some of the problem may have been that half of the answer “isomorphous substitution” didn’t show up on the exam.  However, it appears as though, CEC is still an area that people are struggling with.

Do you find cation exchange capacity a topic that is difficult to understand?

Part III.  Short answer and calculations

Questions 3 and 5 were calculation questions.  These questions were typically done relatively well; however, there were some clear problems with both calculations.  Units, units, units.  Almost everyone who knew how to do the calculations in question 3 forgot to put the answer in kg/hectare furrow slice.  Almost 50% of the class got 2.5 out of 3 on this question because they forgot the correct units. Question 5 was similar too,  a lot of people forgot to express the answer in cm³.

Another issue encountered was converting units.  It’s always a good idea to double check the number of zeros you have when dealing with metric conversions.  As well, if you aren’t sure how to proceed on a calculation question, it’s a good idea to try to draw the dimensions out or at least try something.  Many students left question 5 completely empty and that meant losing 4 possible marks. 

Bulk density.  This is a concept that has been stressed in class a lot and several clicker questions have focused on bulk density.  The majority of students were on the right track when it came to question 4, but just needed to fill out their answer.  The average mark was 1.6 out of 3 possible marks for that question.

Part IV. Short answer (Question 6-8)

This is where the midterm started to go quite poorly for most people.  For questions 6 to 8, the average mark out of 5 was less than 2.5.  This is an area where people lost a lot of marks.  The majority of marks lost were due to lack of information provided.  In general, one sentence is not a sufficient answer for 5 marks.  Individuals who used point form typically did better because they usually had 4 or 5 points listed.  The basis for the answers for each of these three questions comes directly from the class notes.

Question 6.

Briefly explain how topography can influence the soil formation process.

These two slides are directly out of the topography lecture notes.

Question 7.

What was the last period of glaciation (Wisconsin period) such a fortunate event in Saskatchewan prehistory?

Slide is from the glaciation lecture.

Question 8.

What is soil structure? What are the benefits of good soil structure?

Last two slides from the soil structure lecture

On questions 6, 7, and 8, students averaged approximately 7 marks out of a possible 15.  This was a huge loss of marks for most people, especially when the exam was only out of 55 marks.

Part V. Long answer

The long answer question was quite interesting because 40 students out of 60 selected Option A, probably thinking it would be simpler.  However, in terms of clicker questions presented in class, 3 questions provided the direct basis for the answer of Option B and only 1 clicker question dealt with Option A.

Option A.

The clicker question presented on this topic was, which soil genesis process does water NOT participate in?

-physical weathering

-chemical weathering

-biological weathering

-leaching

-parent material deposition

There was no correct answer for this question because water participates in all the processes listed.  For full marks, you could have listed the 5 processes and briefly described each one.  The average mark was 5.1 out of 10 for Option A.

Option B.

For the 20 brave souls in the class who attempted this option, there were plenty of hints dropped in the clicker quizzes.

Clicker question 1 on CEC

Which soil characteristic does CEC not influence?

-soil fertility

-soil moisture

-soil texture (correct answer, CEC does not influence texture, but texture DOES influence CEC)

-soil structure

-soil pH

Clicker question 2 on CEC

What soil property is NOT influenced by the negative charge on clay and organic matter (CEC)?

-soil fertility

-soil water holding capacity

-soil pH

-soil structure

-soil temperature (correct answer)

Clicker question 3 on CEC

A soil with a high cation exchange capacity will have

-a high clay content

-ability to resist leaching loss of cations from soil

-ability to supply more nutrient elements to plants

-all of the above (correct answer)

The correct answer for Option B could have included listing soil fertility, soil moisture/water holding capacity, pH, soil structure, etc. and briefly describing how they are affected by CEC.  The average mark for Option B was 4.5 out of 10 but that is hard to compare to Option A because so few people even selected Option B.

Overall impressions and suggestions

I’ve included a few suggestions for writing exams just based on what I saw in the results from the midterm. 

1. Take the time to write down anything you can think of for a topic, you never know, you might get partial marks. 

2. If it takes you a long time to write, start with the long answer questions and leave the multiple choice and matching to the end because they go faster. 

3. If a question is worth 10 marks, chances are you need to list 10 things or list 5 things and describe each item in some detail. 

4. Make sure the length of your answer reflects the number of marks allocated to the question. 

5. When studying, try to focus on topics that are stressed repeatedly in class, guaranteed they will show up on an exam in some form (most likely a long answer).

Did you find the clicker questions or the blog helped provide information or hints as to what would be on the midterm?

Other soil parent materials found in Saskatchewan

In our previous blog we examined soils developed on glacial till and glacio-lacustrine parent materials. These materials are the foundation of the majority of agricultural soils in this province. Let's briefly look at two other parent materials that represent much smaller areas of the province and produce soils that have limited or no agricultural capability. These parent materials are called Fluvial and Aeolian materials. Fluvial refers to relatively coarse parent material deposited by fast moving water. This water was mostly produced during the melt phase of the last glacial period.  Aeolian materials, in contrast, are wind blown sediments mostly deposited by the prevailing winds at the end of the last glacial period. Aeolian materials, if coarse, are called Dune Sand, whereas, finer silty textured materials are called Loess. When the great ice sheets had melted and retreated there was a period where the exposed parent material was not vegetated and very susceptible to wind erosion.

Fluvial Parent Material

  

Soils developed on fluvial parent materials generally have a very limited agricultural potential.  The precise nature of these materials is determined by the speed of water flow during deposition. In general, the more swiftly that water flows, the coarser the resultant material. Figures 1 and 2 are examples of comparatively fine fluvial material which has some agricultural potential. Figures 3 and 4 provide examples of coarser materials with virtually no potential for crop production.

Figure 1. Field developed on comparatively fine fluvial parent material

Figure 2. Close up of Figure 1, courtesy T. Yates

Figure 3. Fluvial soil profile exposed, courtesy of K. Van Rees

Figure 4. Extreme example of fluvial parent material, courtesy of D. Anderson

                                            Aeolian parent material

Figure 5. Aeolian parent material, Great Sand Hills of SW Saskatchewan

In Saskatchewan, the only significant areas of Aeolian (wind blown) parent materials are found in the Great Sand Hills and the sand dunes of Lake Athabasca. This dune sand material has extremely limited agricultural potential even as pasture. Finer Aeolian material (silt sized soil material) can also be transported by wind. This material is call Loess.  There is very limited area of loess type soils in Saskatchewan however loess is an important parent material for agricultural soils of USA and China.  It is difficult to recognize soils developed on loess parent material because the deposit is generally thin and follows the undying topography.  A microscopic examination of a soil sample is really needed to confirm loess. In Saskatchewan, small areas of loess parent material are located adjacent to coarser sand dune deposits. Hence some loess type soils are found on the eastern side (downwind) of the Great Sand Hills. When these silty-textured soils experience beneficial climate they are capable of good crop production.

From glacial till and glacio-lacustrine parent material to soil

We have examined the general characteristics of parent materials common to Saskatchewan, let us now turn our attention to the agricultural characteristics of these soils.

a. Glacial till
Glacial till parent material produces the largest portion of agricultural soils of Saskatchewan; about 60% of total arable acres in the province. Glacial till parent material was carried and deposited by the southward advance of the great ice sheets which covered the province during the last ice age. Glacial till is very mixed or heterogeneous material because it includes all types and sizes of materials that were scooped up and carried in the advancing ice sheet. Glacial till parent material therefore contains all particle sizes from clay to boulders. Fortunately the glacier encountered a large quantity of relatively finer materials, hence the average texture of glacial till soil in Saskatchewan is loam to clay loam. The amount of stone included in the material is variable, and to some extent the luck of the draw. As I indicated to you in my first blog, my farm has some disagreeably stoney fields.  These fields still produce well when it rains, but to this day, need a lot of stone picking. The more or less uncontrolled (random) release of parent material from the melting ice sheets produced irregular topography ranging from gently (figure 1) to strongly (figure 2) rolling landscapes. The more rolling the landscape the more likely the fields are to be dotted with sloughs and wet spots. In addition, the steeper the slopes, the greater the likelihood of soil erosion. Notice the lighter coloured knolls in figure 2.

Figure 1, gently to moderately rolling glacial till landscape

Figure 2  Rolling to strongly rolling glacial till landscape

b. Glacio-lacustrine parent material

Lacustrine parent materials were deposited in glacial lakes created during the melt phase of the ice sheets. These glacial lakes were formed because the melt water could not move northward because it was dammed by the ice sheet nor could it flow southward because land to the south was of higher elevation. The water in these large bodies of water was calm, particularly in the winter when ice covered. Therefore the water only carried fine soil particles in suspension. These fine particles slowly settled to the lake bed. Soils developed on these "old lake beds" are fine textured, generally level and stone free (figures 3 and 4). They are particularly well suited for production of lentil, chickpea and other short stature crops

    
                     Figure 3  Lacustrine landscape located in the Black soil zone of Saskatchewan

Figure 4  Lacustrine landscape in Brown soil zone of southern Saskatchewan

In the end most producers would choose lacustrine parent material if they had a choice. Most of us however don't have that choice, we have to play the cards we are dealt. Don't give up on till soils, if they are fertilized appropriately and it rains accordingly, they are capable of excellent production. Don't forget to include the important health benefits associated with glacial till soil; high quality exercise while picking stones.

The nature of parent materials in Saskatchewan

  We have discussed the influence of parent material, climate, vegetation, topography, time and man on soil genesis or pedogenesis. This post is dedicated to exploring more fully the role of parent material in the pedogenesis of Saskatchewan soils. Parent material is unconsolidated rock and mineral material which subject to the forces of weathering produces a soil with its characteristic horizons. This slow paced weathering process (encompassing 100's to 1000's of years) commences at the surface, the interface between parent material and the environment. With time, the forces of weathering exert their influence to greater and greater depths, however the intensity of the process is reduced with depth. Soil layers or horizons emerge, first an A horizon and subsequently a B horizon. If the forces of weathering are more intense the depth of the A and B horizons will generally be greater.  At a certain depth, which is determined by weathering intensity, the pedogenic forces have little or no affect on the rock and mineral material. At this point we recognize the C horizon, the more or less unaltered parent material.

                               
       Figure 1   Typical horizon development grassland soil                

  The last ice age in Saskatchewan's prehistory is responsible for deposition of most parent materials. A consequence of the glacial activity is the incorporation of large amounts of limestone into this parent material. Saskatchewan parent materials are therefore generally referred to as calcareous, with neutral to basic soil pH values. In the 10,000 to 15,000 years since the last glaciation, the lime content of the A and B horizons has slowly weathered away, however the C horizon which is relatively unaffected by weathering  has retained its lime content. The presence of lime is easy to detect by applying dilute hydrochloric acid (HCL).  The HCL releases CO2 from the limestone and produces a characteristic fizzing or effervescence. The depth to the C horizon can be easily determined by exposing the soil profile to dilute HCL. Using a plastic squirt bottle, apply a small stream of acid to the soil profile starting at the surface and proceeding downward. When fizzing appears it is an good indicator that you have reached the lime and therefore the C horizon. Visit SLSC 240 online and view the discussion by Dr. Anderson about soil horizons, He makes use of HCL to locate the C horizon. Go to the online course here then to module 6, section 6.1, and view the quicktime video discussing soil profile identification.

                                                       

Writing a term paper, the good, the bad and the ugly

One of the more difficult parts of my job as a teaching faculty is to train students in the production of good quality term papers. In any agricultural science, the production of  a quality term paper requires it conform to certain standards with respect to format, writing style and scientific content.  Student must master all three components in order to score well with their papers.

I hope to provide insight into the process I employ to arrive at a term paper grade. Perhaps by understanding my thought process during grading, you will produce a paper that achieves a better score. Come March of this term I will be required to grade more than 60 SLSC 240 term papers and this is not my only course this term. In addition, no two topic are the same, so there is no repeating content as is typical of a midterm or final exam. Any exercise or exam where all student respond to the same question(s)  is definitely easier and faster to grade. It is important to me that I provide a fair assessment for each students term paper whether it be the 3rd or 55th paper I have read.  To achieve that, I must apply a rigorous marking scheme to each paper which segregates the marks into categories. I allocate marks in three general areas:
                                                   1. paper format - 30%
                                                   2. scientific content - 40%
                                                   3. writing style and accuracy - 30%

Based on this allocation of marks a student could theoretically make a mess of the format but still achieve a 70% grade. In practice that does not happen because almost invariably a student who does a poor job of formatting the paper will also have shortcomings in the science and writing components. The following is a list of questions and thoughts I go through as I grade your paper.

 A. Paper format
        1. Does the paper have all the necessary components; title page, abstract, table of contents, list of figures and tables and references?
        2. Are graphs and tables captioned properly, author and date cited?
        3. Is the reference section formatted correctly, alphabetical order etc.?
        4. Are all authors cited in the text listed in reference section and vice versa?

B. Scientific content 
        1. Is the stated topic, as articulated in the introduction, covered completely, accurately and logically?
        2. Is the topic very general or specific (narrower focus)?
        3. Are the scientific concepts presented of a complex or simple nature?
        4. Are the number of references cited large enough to indicate that the topic has been thoroughly researched?
        5. Is the data presented useful? Does it support and clarify the concepts presented?
        6. Is there evidence of interpretation or synthesis of data as opposed to simply reporting it?

C. Writing and grammar
        1. Is the paper grammatically sound?
        2. Is sentence construction such, that meaning is clear?
        3. Does the paper contain complex and / or cumbersome sentences which cloud the meaning?
        4. Is scientific terminology used correctly?
        5. Are paragraphs constructed to provide a logical flow of concepts and ideas?

It is difficult to be more specific about the actual grading process, table 1 is an attempt to shed some light on the process.

Table 1. A general description of the mark allocation for SLSC 240 term paper.

Writing a well crafted term paper requires a lot of practice. In my own case I was 20 years into my career before I felt that my writing skills had really matured. To those students in 1st or 2nd year, I am not expecting miracles; however, if you pay attention to the key components of paper writing and ask for help if necessary, you can certainly achieve an acceptable grade.

How parent material influences soil pH

Although the pH scale ranges from 0 to 14, most soils have pH values between 4 and 9.  Many soils of the world are acidic for a variety of reasons including parent material, weathering and pollution.  Overtime soils have a general tendency to become more acidic.  The pH of a soil is often a limiting factor in plant nutrient availability. Soil pH may affect the water solubility of a nutrient and therefore plant uptake of that nutrient.  A common agronomic practice associated with highly acidic soils is liming.  Lime is a common amendment added to raise soil pH.  However, as was discussed in class, a soil may have high reserves of H+ ions which means that large amounts of lime would have to be added to have an impact on the soil pH.  The reserve acidity is dependent on soil texture and cation exchange capacity.  An example of this would be a high clay soil with high organic matter content which results in a high buffering capacity.  In a soil like this, it would be very difficult and expensive to change the soil pH.

Parent material can exert a strong influence on soil pH.  Materials such as shale, sandstone and granite generally produce more acidic soils.  In Western Canada however, soils are generally neutral to basic and resist acidification.  This is in large part due to the limestone parent material.  The soils in Western Canada therefore tend to resist acidification hence are buffered in the basic pH direction.  Saskatchewan has about 45 million acres of cultivated soil, of that 17.5 million has a pH > 7.0 and 1.5 million has a  pH value of > 5.5.  This is a result of parent material and the relatively recent glaciation of the soils.  The general bedrock geology (parent material) can be observed in Figure 1.  The yellow and orange areas on the map indicate areas of limestone parent material.  This band of limestone strongly influenced the distribution of pH values seen in Figure 2.

Figure 1. Bedrock geology of Saskathcewan.  Yellow and orange areas indicate limestone parent material.
Image from Atlas of Saskatchewan, 1969

Figure 2. pH values of Saskatchewan soils.
Image prepared by H.P.W. Rostad, J.J. Kiss, and A.J. Anderson, 1983, University of Saskatchewan

The soils on the east half of the province are dominated by basic and neutral soils while the soils on the western half of the province are neutral to acidic (Figure 2).  When the last glaciation occurred the thickest part of the glacier was on the east side of the province and scraped over the widest band of limestone parent material (Figure 1 - orange area).  Figure 3 illustrates the retreat of the last glaciation in Saskatchewan.  It was the advance and retreat of the glacier that incorporated the limestone parent material into the soil.  The glacier was thinner on the western half of the province.  The limestone band is also thinner in the northwestern part of Saskatchewan (Figure 1 - yellow area), so less limestone was incorporated into those soils.  The glaciation and parent material are the reasons that our agricultural soils are predominantly calcareous and have neutral to basic pH.  Once the lime has been exhausted though, Saskatchewan soils will lose the capacity to buffer against acidification.

Figure 3. Glacial retreat in Saskatchewan.

What constitutes desirable soil structure?

My previous blog discussed changes in Western Canadian cropping systems over the last 40 year period and the benefits that have accrued to soil organic matter, soil structure and water infiltration because of those changes. The question not explored thus far is, why have those cropping system changes had a beneficial impact on soil structure? The answer lies largely in the impact of these system changes to the biological processes that influence soil structure development. The other key issue is that tillage, which is so deleterious to soil structure, has been greatly reduced with the advent of  min-till /z-till systems.

Before discussing soil structure development further it is appropriate to describe what constitutes good soil structure. Fundamentally it involves the development of a relatively stable soil aggregate system that produces many crack/pores/fissures etc which support/enhance the normal vertical movement associated with water infiltration, gas exchange and root growth. In contrast, soil structures with a horizontal orientation produce barriers to the normal vertical processes and hence are considered undesirable.

Figure 1. A soil profile showing very good soil structure.

Figure 2. A soil profile showing undesirable structure in the second horizon.

Plant root systems, particularly dense fibrous root systems, produce beneficial soil structure.  Roots have the ability to enmesh or knit together soil particles into larger desirable soil aggregates. In addition the normal metabolic processes of roots involve the release of various slimes, gums and mucilages. These organic compounds  act as nature's cement, to further stabilize aggregate formation. Development of stable aggregate structure is desirable because well-aggregated soil can more rigorously resist the destructive powers of wind and water erosion. The forces of tillage however are likely to destroy even relatively stable aggregates.

Crops and cropping systems also enhance water infiltration because of the influence of old root channels associated with previous crop growth. These channels provide a rapid pathways for water infiltration
(see figure 3); however, tillage will destroy these channels or at least destroy its continuity. Pore continuity refers to a pore system connectedness. An optimum pore system will consist of cracks, pores, or root channels that support a continuous (uninterrupted) flow of water from the soil surface to subsurface. Intensive tillage tends to disrupt the entire pore system to the depth of tillage. The subsurface pore system is therefore no longer connected with the surface, reducing water infiltration to greater depth.

Figure 3. Microscopic view of an old root channel.                                                                                   

Another important component of water infiltration is preferential flow. Preferential flow describes water movement in soil via preferred pathways. In essence, soil water moves via the path of least resistance rather than moving  through the entire soil matrix. In this context I recognize two types of preferential flow, movement though macro pores and root channels.  This concept is illustrated in an experiment by Dr. Bing Si, College of Agriculture and Bioresources, University of Saskatchewan. Dr Si applied water, amended with a greenish dye, to the surface of a heavy textured soil to assess water infiltration. The irrigated area of the soil profile was later exposed with the use of a small backhoe to examine water movement. The path of the dye clearly shows the importance of the macro pore systems, particularly at depth (figure 5), in enhancing the naturally slow infiltration associated with clay textured soil.

Figure 4. Moisture movement into soil at surface.

Figure 5. Moisture movement in the 9 to 14 inch segment.                                 

In Figure 4, the dye pattern reveals a more general infiltration process through the bulk surface soil with some indication of preferential flow. Deeper in the profile (figure 5) the influence of preferential flow is more clear, water infiltration is more rapid and deeper than expected. Water and associated dye has taken the path of least resistance and has not infiltrated the entire soil profile. This concept is important when considering possible contaminant movement into a heavy textured soil. Extensive crack development supports preferential flow and thus has the potential to move a contaminate more swiftly and to a greater depth than expected based on its natural slow infiltration properties.

In summary, a reduction in number and intensity of tillage operations combined with a continuous cropping system, supports desirable soil structure development and superior water infiltration. Increased organic matter and reduced mechanical disturbance allows the development of stable soil aggregates which produce a vertical pore system that makes possible more rapid entry of water, even in fine textured soils. This improved infiltration is the result of stable soil structure, production and maintenance of root channels, enhanced pore continuity and the potential for preferential flow.

Soil structure, water infiltration, cropping systems

The rate and nature of water movement into soil (infiltration) is governed by a number of soil and climatic characteristics. They include soil texture, structure, organic matter and slope, crop surface residue, kind and density of crop growth, as well as rainfall intensity/duration and soil moisture content. Western Canada is located in a water limited, semi-arid environment, therefore from a crop production perspective, infiltration and storage of incidence precipitation is clearly a more desirable outcome than runoff. Fortunately changes to our crop production systems over the past 30 to 40 years have helped to improve water infiltration and storage.
During the first 80 to 90 years of crop production in Western Canada, tillage was a dominant practice. In the beginning ploughing of the native prairie removed the thickly rooted perennial grasses to make way for cereals such as wheat, oats and barley. Cereals root systems are much less extensive than the native grasses they replaced and therefore have considerably less beneficial impact on soil structure. In addition the practice of summer fallow (leaving the land idle for an entire growing season) necessitated multiple tillage operations in the fallow year to control weeds. While effective in controlling weeds, routine tillage had a serious negative impact on soil structure. To make matters worse, the lack of crop residue during the fallow season did not support production of new organic matter rather it accelerated the degradation of the existing soil organic matter reserves. In short, the system had severe negative consequences to soil organic matter levels (on average 40% reduction in organic matter content) and to soil structure (beneficial structure destroyed). Lack of crop cover and deteriorating soil structure reduced water infiltration. Summer fallow fields therefore experienced greater runoff and associated soil erosion during heavy rainfall episodes. In rolling terrain, see figure 1, it was not unusual to see the landscape dotted with potholes and sloughs, great for waterfowl, but not desirable from a crop production perspective.

Figure 1. Typical example of potholes in a gently rolling summer fallow field

By the 1980's advances in seeding equipment and fertilizer technology ushered in the era of minimum till/zero till seeding. This was combined with continuous cropping which revolutionized Western Canadian crop production systems. Min-till / Z-till conserved crop residue on the soil surface, and made possible more intensive annual cropping systems than had previously been practiced. Greater crop residue production and hence organic matter input, coupled with less tillage, produced significant improvements in soil structure. The sloughs and potholes which dotted the landscape during the 60's and 70's began to disappear as the combination of decreased tillage, increased surface residue, increased soil organic matter and improved soil moisture infiltration, significantly reduced water redistribution in the landscape, see figure 2. While good for farmers, this cropping system is definitely less desirable for water fowl.  I have personally observed fields that have been converted to Z-till and continuous cropping for more than 30 years. These fields have experienced substantial productivity gains, with the greatest improvement occurring on the upper slope positions. I attribute part of that productivity gain to improved infiltration and  moisture retention on the upper slopes.  An added benefit of narrowing the productivity potential between upper and lower slope is crop maturation.  Crops mature more uniformly on these fields. This is very beneficial at harvest because now upper slope and lower slope crop is ready to harvest at the same time.

Figure 2.  Rolling Z-till field with uniform stubble cover, no potholes visible

Before I am called to task over my remarks, I want to point out circumstances where sloughs and potholes do return. The likely scenario is when soils enter the winter period with better than average soil moisture content. This soil condition is coupled with heavy winter snow fall and rapid spring snow melt. The frozen soil prevents normal infiltration and a rapid melt of a heavy snow pack will generate allot of water with no place to infiltrate.  Theses conditions lead to greater than normal runoff, therefore sloughs and potholes  return to the landscape.

Soil Moisture - too much of a good thing?

Anyone growing up in Saskatchewan is well acquainted with soil moisture even if they don't realize it.  Everyone can remember a summer when farmers would say things like, "we need at least two inches of rain in the next week for the crops to be decent this year."  People like to talk about moisture a lot in Saskatchewan, or more accurately, the lack of moisture.  Saskatchewan is a mid-continental, semi-arid province which means that we rely on precipitation to replenish the majority of soil moisture.  It isn't just rainfall that is important either, snowfall accounts for approximately one third of the annual precipitation.  As well, there is a geographical distribution of precipitation in Saskatchewan with higher annual precipitation in the north declining to the south.  However, it seems more often than not, that precipitation is  widely variable and can strongly affect how crops will perform from one year to the next.

2009 and 2010 are recent examples of how dramatically moisture can change in two consecutive years.  In 2009, conditions were cool and dry.  Most of the stress experienced by crops was due to lack of moisture and lack of heat.  Soil moisture completely changed in 2010 when the rain wouldn't stop all summer.  It was difficult to seed crops in the spring because it was so wet and many fields remained flooded for much of the summer.

Map of Saskatchewan showing cumulative rainfall throughout growing season in 2009.  Map is from the Government of Saskatchewan 2009 Crop Report.  A full version of the report can be found at http://www.agriculture.gov.sk.ca/crprpt091222

Map of Saskatchewan showing cumulative rainfall throughout 2010 growing season.  Map is from the Government of Saskatchewan 2010 Crop Report.  A full version of the report and maps can be found at http://www.agriculture.gov.sk.ca/crprpt101104

Just at first glance, it is obvious that the two years were very different in regards to rainfall.  The different rainfall regimes influenced soil moisture and crop production dramatically.  Many of the crops grown in Saskatchewan are more drought-tolerant than moisture tolerant, so the large surplus of moisture did not benefit crops particularly well in 2010.  According to the Saskatchewan Crop Reports, in 2009 crops were average to above-average in quality and yield.  However, in 2010 the yields were average to above-average, but the quality was below-average.  There were several reasons for this including seeding late, crop loss due to flooding, plant stress from too much moisture, and plant disease.  All of these issues were related in part to excess soil moisture.

The soil moisture surplus in 2010 also carried through to 2011.  In the fall of 2010, much of the soil was fully saturated or had a higher moisture content than usual for that time of year.  This meant that when the ground froze, much of the pore space was filled with water.  In the spring of 2011, areas all over Saskatchewan experienced flooding because the winter snowpack started to melt and there was very limited infiltration into the soil.  My field site was not spared from the flooding.  All of my study plots were submerged for most of the spring in 2011.

Water as far as the eye can see.  Me (Morgan) at my field site near Scott, SK in April 2011.

Do you have any stories about the excess moisture we experienced in 2010? Or the flooding in 2011? Please feel free to share your stories in the comments section.

The role of soil moisture will also be discussed in more detail later in the soil formation and organic matter posts; however, it is clear that soil moisture is vital to crop production, but sometimes you can have to much of a good thing.

Information and maps from the Government of Saskatchewan Crop Reports was obtained from

http://www.agriculture.gov.sk.ca/Crop-Report.  For more detailed information, check out the Crop Reports from various years.

Thoughts about soil texture

 Soil texture is one of the most important and fundamental properties of soil. It not only governs the behaviour of  soil with respect to water storage and movement, but additionally influences a range of other properties such as natural soil fertility, soil structure, soil erodibility etc. In Western Canada finer textured soils, which possess excellent water storage capability and superior fertility status, are considered the most desirable for semi-arid crop production. Figure 1 provides a very generalized look at the distribution of various soil textures in the province. The areas labelled fine or very fine would generally be clay or heavy clay textured. The medium and moderately fine soils would be some form of loam texture and the course and moderately course would be classified as sand to loamy sand. We will learn shortly that soil texture and parent material deposition are directly related. You may notice that the medium textured materials (orange color) dominate the Saskatchewan landscape, they represent about 60% of agricultural land of Saskatchewan. Soils of medium texture are normally formed from materials deposited during the advance of the last glacial period in Saskatchewan's prehistory. Soils of fine and very fine texture were generally deposited in the still waters of lakes formed during the melt and subsequent retreat of those great ice sheets.

Figure 1. A generalized map of soil texture in Saskatchewan, courtesy of D. Cerkowniak, SK Land Resource Center, AAFC, Saskatoon, Saskatchewan.

Saskatchewan is blessed with a surprisingly large acreage of soils formed from fine materials deposited in glacial lakes (areas mapped in dark green). These lakes were formed during the melt phase (deglaciation phase) and remained for long periods of time because the melt water was trapped between the retreating ice sheet to the North and the land of higher elevation to the south. In a subsequent section of the course that examines soil formation (genesis) in Saskatchewan, we will look in more detail at the various depositional processes that occurred during the last glacial period.

What is the best soil texture?

Based on my previous discussion you may have come to the conclusion that a clay to heavy clay soil is the "best" texture. A better view is;  the best soil texture depends on its intended use.  Dry land farmers tend to pay top dollar for fine textured soil for a reason. These soils posses excellent natural fertility and water holding capacity which supports good dry land crop production.  These soil usually have additional benefits such as level topography and little to no stones. These characteristics further add to their attractiveness for crop production. That same clay soil, however, if located in a high rainfall area, would be much less suitable unless you were considering rice production.  A gardener, in contrast, may prefer a medium textured soil (loam, silt loam to clay loam) because he /she often has a supplemental source of water so moisture holding capacity is not as important. An additional benefit of medium textured soils is the ability to absorb water more rapidly and therefore experience less runoff.  Medium textured soils are also easier to work (till) than there heavy textured counterparts, because they are less sticky when wet and less likely to get rock hard when very dry. This point of view would also hold in a field situation if it were being developed for irrigated production. A medium textured soil is generally preferable, because irrigation systems apply water at fairly high rates and these soils are able to absorb the water with little or no runoff. In contrast, irrigation on heavy soils is difficult and requires specialized application equipment.

In the world of engineering and construction, the view of ideal soil texture may be quite different. The construction of roads and building requires soils which are stable and allow water to drain away quickly. In this case coarse textured soils are preferable, they are less compressible and do not exhibit shrink/swell behaviour that clay soils do during wetting and drying cycles. Therefore cities like Regina or the east side of Saskatoon which are built on clay to heavy clay soil are notorious for cracked and heaving basements. Houses built in these area must employ specialized construction techniques to avoid damage to basements.

Wet clay soils can be a challenge

Behavior of heavy clay when dry is also challenging

A final thought about soil texture and crop production. 

The adoption of modern crop production techniques including direct seeding/minimum and zero tillage has narrowed the traditional productivity gap between the fine and medium textured soils. Clay soils were particularly superior when farmers employed the practice of summer fallow. The objective of summer fallowing was to store extra soil moisture for subsequent crops during the 18 month fallow period. The storage capacity of the fine textured soils is high which made them especially effective for that purpose. Modern minimum or zero-till production systems in combination with continuous cropping have a much shorter period (6 months) of moisture storage,  so storage efficiency is a less important soil characteristic.  The reduced tillage systems we now employ retain more crop residue on the soil surface. This decreases moisture loss via evaporation and therefore contributes to improved storage.  Improved fertility practices have also improved crop water use efficiency so in the end the yield differences between the heavy and medium textured soils has narrowed substantially.  In the end, to rationalize the extra $ to buy C to HvC soil, one must place a high value on level topography and few stones, because the yield differential between medium and heavy textured soils is often slim to none.

Morgan's connection to soil

I have been asked numerous times "why soil?" when I tell people what I do.  Being a soil scientist is not something most people are familiar with.  Its not something recognizable like doctor, lawyer, or accountant, but I love studying it.

I suppose a love of soil is in my blood.  I come from a long line of farmers who have worked on the land for many generations.  I grew up on the original homestead that my great-great grandparents settled in 1903 and there was always a sense of how important the land around us was.  I spent my childhood helping out on the farm and being surrounded by farming activities constantly.

My childhood spent on the farm.

However, it took me a while to figure out that I wanted to study soil.  No one ever tells you that you can be a soil scientist.  I thought if I went into the College of Agriculture, I would become a farmer and that wasn't something I was interested in when I was 19.  I wanted to be an environmental scientist, so I started out in Physical Geography; however, eventually I started hearing about some amazing courses being taught in Soil Science.  It was then that I started taking a few of these classes and quickly realized there was a lot more to soil than just farming.  When you think about it, after air and water, soil is right up there with things necessary for sustaining life on Earth.  It provides us with food, stores and purifies water, provides and recycles nutrients for plants.  Soil is connected to so many aspects of our lives and yet we often don't take good care of it.  I was so enamored with soil by then, that I spent a summer working in the Department of Soil Science as a summer student.

I finally finished my undergraduate degree with a BSc in Environmental Earth Sciences and headed to Calgary to find a job.  I worked as an environmental scientist with a consulting company for a couple years and I soon discovered that most of the work I did involved soil.  Soil was usually what was being contaminated and impacted by pollutants. But I also learned that soil microorganisms have amazing capabilities to reduce those contaminants if we supply them with the substrate that they need.  Eventually I realized I wanted to learn more about soil and decided to pursue my MSc in Soil Science back in Saskatoon.

Photo courtesy of Rich Farrell

Studying soil science has allowed me to combine two areas that I never realized went together so well: environmental issues and agriculture.  Soil is key to agriculture, but environmental issues are becoming more and more important to look at in every aspect of our lives.  Most of my work now focuses on greenhouse gas emissions from different crops and crop rotations.  So 'why soil?' - well, studying soil allows me to combine my interest in the environment and my life long experience with farming.

Collecting greenhouse gas samples from agricultural plots

My connection to soil - Terry Tollefson

Welcome to SLSC 240 and to our course blog. In the next three months we will examine key physical, chemical and biological components of soil and relate those properties to soil productivity. Our course consists of 39, fifty minute lectures; not nearly enough time to explore these concepts in any detail. I hope  this blog will fill some of those gaps by offering you practical Saskatchewan examples of these soil properties. Before proceeding however, I have decided to give you a brief look at my personal background which may explain why I have made soil science a career.
    I believe that my farm background was responsible for awakening an early interest in soil. I  grew up on the family farm in southern Saskatchewan near the little elevator town of Ettington. That early interest in soil has evolved into a life long connection with soil, both practically and academically.  My claim is based on the fact that for the last 30 years I have taught soil science in the College of Agriculture and maintained an active role in the family farm at the same time.
   My family ties to the land go back to 1909.  My grandfather came to Canada as a young Norwegian Immigrant hoping to take advantage of the promise of farm land to homestead in Western Canada. There was no opportunity for him to farm in Norway, family holdings were very small with little chance to expand. Only 3% of the Norwegian land base is suitable for agricultural production.  The rocky and mountainous landscapes which dominate most of Norway may have influenced my grandfather's choice of land when he arrived in Saskatchewan.  He appeared to be unafraid to select land that was stoney or hilly or both. Figure 1 is an early view of the farm and grandfather seeding one of those rolling stoney fields.

Figure 1: Planting on the farm - precise date uncertain, approximately 1940

In 1948 my father took over the farm and by the 60's my brother and I were old enough to shoulder some responsibility. In those days farm kids did chores as soon as they were able and worked in the field  when old enough to pilot a tractor. I shudder to think how young that was.  One field operation in particular allowed me to be up close and personal with the land, that job was stone picking.  There was a constant need to pick stones to reduce wear and tear on seeding and harvest machinery. Back then, rocks were picked by hand and loaded into a truck or tractor and wagon. I was fortunate that horses were no longer in use by the time I was old enough to pick stones, so I never experienced picking rocks with a team of horses and a stone boat. I became very familiar with every farm field because I walked them many many times over the years. I realized early on that the ability of these fields to produce crops was quite variable and at times I wondered why.

Figure 2: Planting equipment on the farm in 1976

During the seventies I studied at the U. of S. College of Agriculture and received an M.Sc. in Soil Science.  After graduation the farm was still beckoning so in 1981 I  made a career choice that lasted 22 years. I farmed during the summer months and taught soil science during the winter at the U of S. The science of agriculture grew dramatically during that time and I was part of one of the largest teaching and research Colleges of Agriculture in Canada. I was continually exposed to the most up to date production information and used it to advantage on the farm.  In 2004, I decided to move to a full-time position within the College so I now limit  my "farmer habit" to 2 week at seeding and 2 weeks at harvest.
     I intend to bring my practical experience to the classroom to  ensure that you recognize the importance/application  of soil science principles in current production practices. I also hope that you will grow in your appreciation of just how precious our Saskatchewan soil resource is.

Figure 3: Direct seeding on the farm in 2008

Please consider joining the SLSC 240 blog. Tell us about your experiences with soil, good or bad? Where do you live, what is the soil like in your area?