Author: Dwayne L. Beck, Ph.D.

Manager of the Dakota Lakes Research Center

Associate Prof. of Plant Science

South Dakota State University

INTRODUCTION:

Prior to discussing the subject of rotations, it might be valuable to furnish some background information. The techniques and data to be presented were developed at the James Valley Research Center located near Redfield, SD (approximately 130 mi. south, and 65 miles west of Fargo, ND). This facility, at the time it was closed on Dec. 31, 1989, consisted of a 200-acre main station plus a quarter and an eighty of additional land in the vicinity. Soils in this area are developed in lacustrian sediments left by the glacial lake Dakota. This makes them similar to those in eastern North Dakota and Manitoba that developed in the remnants of Lake Aggassiz, with the exception that the soils are lower in organic matter due to the warmer, drier, environment. The soils are medium to heavy in texture (salt loams, salty clays and salty clay loams), show slow permeability when conventionally tilled, have goo water holding capacity, and are prone to wind and water erosion. Primary crops grown in the area include wheat, barley, rye, oats, corn, sunflowers, sorghum, and soybeans. Soybeans are relatively new but have become quite popular. Acreage of soybean in Spink County has grown from 1,900 acres in 1979 to over 100,000 acres in 1989. Sunflower acreage has shown dramatic declines during this period.

The station normally receives slightly over 18 inches of precipitation annually although this has not been the case in the last few years. Approximately 100 acres on the main station was irrigated; all other land at Redfield and the three-quarters at the new Dakota Lakes Research Center near Pierre were dry land in 1989.

The role played by research station personnel in South Dakota includes small plot research trial support; field scale research and uniform production farming demonstrations. The stations are not well equipped to plant or harvest small plot trials, but station staff assist researchers from the main campus and USDA laboratories when they plant or harvest. We also perform almost all site preparation, plot maintenance, data collection, and treatment application duties. Although these small plot trials covered only about 100 acres in 1989, they consumed the majority of the labor resource's available.

The equipment used for the almost 900 acres of cropland at the Redfield and Pierre stations in 1989 is extremely meager as compared to that used by research centers of comparable size in other states and provinces or by farmers. Two 75-85-hp tractors perform all field operations.

One is a 1967model 706 IH, the other a 1980 model 2840 JD. Other frequently used equipment includes a 12.5-foot no-till drill, a row crop ridge-planter, and a high residue row crop cultivator. We also own some old tillage implements such as an 8-foot chisel (digger), a 15-foot field cultivator, a 16-foot tandem disk, and a 5-bottom plow. These are used only rarely for land preparation and treatment application in small plot studies. Spraying is handled with a homemade pull type sprayer covering either 37.5 or 25 feet depending on the job to be performed. Harvesting is done with a 4400 JD combine, a 250 Bu. grain cart equipped with scale and a small semi-tractor and trailers. We employ two full time technicians. These two people and I perform almost all fieldwork and a substantial portion of the research operations at the stations. College students are hired during he summers to help with data collection, plot maintenance, and grounds keeping.

The field scale research portion of our program primarily involves replicated strip trials. Strips are normally 25 to 100 feet wide by 350 to 1300 feet long. This is sufficient to allow use of standard sized farm equipment for all field operations. Harvesting is done using the 4400 combine with the grain being weighed in the 250 Bu. grain cart. My staff and I are solely responsible for planning and conducting these trials.

The final portion of our duties involves uniform production farming demonstrations. There are three aspects that enter into this part of the operation. The first is to uniform the fields for research to be conducted in the future. The second is to serve as a method of integrating the knowledge and practices grained from small plot and field scale research projects into a "real world" environment to see how they hold up. And the last is to do what all farmers must do to remain in business: to make a profit. Well over half of our operating budget now comes from profits as compared to under five percent prior to 1983. In two years we expect to be generating about 80% of our operating budget.

Comments regarding the importance of crop rotations to no-till farming will be almost entirely based on field scale research and experiences with uniform production farming. This is not meant to downplay the importance of small plot research or researchers (a resource used extensively to select treatments for trial in field scale studies). But rather stems from the realization that most producers, before adapting new technology, like to have the tries kicked a little harder than is possible in many small plot trials.

You probably have gathered by now that South Dakota State Univ. is in the process of closing the James Valley Research Center at Redfield and opening the Dakota Lakes Research Center at Pierre. The reasons for this go beyond the score this discussion, but include the issues of land ownership, future irrigation development, and dryland research needs. The preference was to operate both stations, but the unwillingness of the present owner at Redfield to sell us the present site and the belief that resources were not sufficient to develop two new sites simultaneously, led to concentrating efforts at Pierre while maintaining some of the work at off station Redfield locations.

TOTAL PRECIPITATION IN INCHES
	1932 Monthly	1933 Monthly	1934 Monthly
January	0.38	0.07	0.05
February	0.10	0.03	0.06
March	0.32	1.98	0.85
April	1.61	0.71	0.12
May	2.07	2.48	0.38
June	4.45	1.96	3.25
July	0.93	4.15	1.29
August	3.95	0.47	0.40
September	0.87	1.42	2.14
October	0.92	0.02	1.54
November	0.20	0.17	0.73
December	0.27	0.72	0.64
TOTAL	16.07	14.18	11.45
April 1 to September 1	13.01	9.77	5.44

The agricultural practice of intentionally planting crops for later harvest most likely began when primitive hunter-gatherers notices plants growing from seeds discarded near their campsites provided a more convenient food supply and often flourished better than those in last years patch. They had unwittingly discovered one of the oldest, most important, and under-emphasized concepts in agriculture, the rotation effect.

They practiced the oldest and simplest form of rotation: farming and moving on. These early bands were nomads who began to stay in one place only long enough to plant, tend, and harvest a crop. As the amount of virgin land in a given area declined and the societal and financial cost of moving increased, the intervals between moves began to lengthen. Eventually, however, crop production would decline to the point that some or all of the members were forced to migrate to other areas. European settlers came to North America looking for rich, virgin, land to farm. The westward movement of settlers in North America contained both new immigrants and a large percentage of farmers from back east; looking for soil that was not "worn out". Even today slash and burn agriculture is practiced in the tropics as a method of rotation.

In areas where virgin land was gone, farmers began developing (through trial and error) farming methods similar to ones being practiced today. The need for and value of rotations became recognized but was viewed by most to be an inconvenience; a constraining force to be mitigated through the use of "improved farming methods", witchcraft, prayer, luck, or even more drastic measures. Intensive tillage, which buried crop residues, was and still is a relatively effective method of reducing the severity of certain foliar plant disease outbreaks when proper rotations are not followed. As the effects of tillage mined the soil organic matter, the need for methods of furnishing adequate nitrogen for crop growth began to appear. This lead initially to fertilizing with animal wastes or other sources of organic matter and later the introduction and widespread use of inorganic nitrogen fertilizers. The rotational benefit of summer fallowing became recognized and the practice more commonplace, especially on the prairies of North America. Improved crop growth following fallow was often attributed to improved soil moisture, when in reality it was largely the result of rotational pest control benefits and fallowing ability to supply two years soil derived nitrogen for use by one crop. The high cost and detrimental effects of fallow (soil erosion, saline seeps, and organic matter decline) led to the search for farming practices that would allow continuous cropping.

Several approaches common in more humid areas were tried on the dry prairies with limited success. Growing a green manure crop from the legume family "wasted" a substantial amount of valuable moisture not only when it was growing but also more importantly as a result of the intensive tillage needed to plow it down. Animal manure was effective, but the larger acreage’s and the less concentrated livestock husbandry methods in the west limited its efficiency. Small population density and large acreage’s, possessing relatively small income potential per acre, negated use of hand labor on a scale comparable to humid regions.

This has led to where we are today. Farmers have found that the use of intensive tillage in conjunction with some combination of fertilizers, herbicides, fungicides, and insecticides will allow them to grow an adequate yield for a given crop in rotations that would produce unacceptable results should any of these tools be omitted. The reasons behind their choice to grow their crop in this manner vary with each situation. Some obviously are economic caused to a large extent by acreage base limitations used as a criterion for participation in the U.S. farm program and Canadian marketing quotas which discourage flexibility in crops grown. Other reasons include tradition and a lack of sufficient information of alternatives to present procedures or let their sons and grandsons change procedures that have worked well for them in the past. This is especially true if a significant number of long term research and demonstration projects have not been performed to prove the viability of new technology. The widespread urban view that farmers use the procedures because large corporations have them "hooked" on new machinery or chemicals or that the producers do it strictly out of greed is hogwash. There are speculators that broke large segments of prairie in the seventies out of greed but they are the exception rather than the rule. The need and desire to maximize profit is the engine that makes a capitalistic system function. It is the reason food is plentiful in both the U.S. and Canada. The best and surest way to eliminate practices detrimental to the long-term productivity of the land, to the environment, or to other segments of society is not through regulation but rather by funding research into developing less harmful alternatives capable of producing adequate and legitimate profit.

Where are farming practices on the prairies headed in the future? Will they follow the conventional approach of intensive tillage used in combination with other modern practices? It is not likely because of increased energy costs and the heightened awareness of the deleterious direct and indirect effects of soil erosion. Will the LISA approach be the wave of the future? It may depend o how "Low Input", "sustainable" and even "agriculture" are defined. Does low input refer only to "unnatural" agricultural chemicals and fertilizers (the vision of many advocates of the LISA system) or to all inputs including machinery, true labor costs, fuel, management, and the costs associated with increased risk? Are all "unnatural" inputs off limits or will the use of safe, cost effective inputs be encouraged? Does sustainable refer to soil productivity, the profitability of the operation, pristineness of the environment, the viability of the local social and business community, or to some combination of these? Does agriculture mean only the production aspects or does it include the industries and business community, or to some combination of these? Does agriculture mean only the production aspects or does it include the industries and businesses that now produce, transport, and supply the inputs and transport, process, and market the output. These and other questions remained to be answered. The only certain aspect of agriculture in the future is that nonagricultural interest will be more heavily involved in determining the agriculture's course. Consequently, all segments of agriculture must do a better job of understanding not only what has to be done to succeed but also why it is done this way and what other effects it has.

This has led to where we are today. Farmers have found that the use of intensive tillage in conjunction with some combination of fertilizers, herbicides, fungicides, and insecticides will allow them to grow an adequate yield of a given crop in rotations that would produce unacceptable results should any of these tools be omitted. The reasons behind their choice to grow their crop in this manner vary with each situation. Some obviously are economic caused to a large extent by acreage base limitations used as a criteria for participation in the U.S. farm program and Canadian marketing quotas which discourage flexibility in crops grown. Other reasons include tradition and a lack of sufficient information of alternatives to present practices. Well-established producers see little reason to change procedures or let

their sons and grandsons change procedures that have worked well for them in the past. This is especially true if a significant number of long term research and demonstration projects have not been performed to prove the viability of new technology. The widespread urban view that farmers use the procedures because large corporations have them "hooked" on new machinery or chemicals or that the producers do it strictly out of greed is hogwash. There are speculators that broke large segments of prairie in the seventies out of greed but they are the exception rather than the rule. The need and desire to maximize profit is the engine that makes a capitalistic system function. It is the reason food is plentiful in both the U.S. and Canada. The best and surest way to eliminate practices detrimental to the long-term productivity of the land, to the environment, or to other segments of society is not through regulation but rather by funding research into developing less harmful alternate as capable of producing adequate and legitimate profit.

Where are farming practices on the prairies headed in the future? Will they follow the conventional approach of intensive tillage used in combination with other modern practices? Is not likely because of increased energy costs and the heightened awareness of the deleterious direct and indirect effects of soil erosion. Will the LISA approach be the wave of the future? It may depend on how "Low Input", sustainable and even "agriculture" are defined. Does low input refer only to "unnatural" agricultural chemicals and fertilizers (the vision of many advocates of the LISA system) or all inputs including machinery, true labor costs, fuel, management and the costs associated with increased risk? Are all "unnatural' input off limits or will the use of safe, cost effective, inputs be encouraged? Does sustainable refer to soil productivity, the profitably of the operation, pristineness of the environment, the viability of the local social and business community, or to some combination of these? Does agriculture mean only the production aspects or does it include the industries and businesses that now produce, transport, and supply the inputs transport, process, and market the output. These and other questions remained to be answered. The only certain aspect of agriculture in the future is that nonagricultural interests will be more heavily involved in determining the agriculture's course. Consequently, al segments of agriculture must do a better job of understanding not only what has to be done to succeed but also why it is done this way and what other effects it has.

With this in mind, the emphasis of this discussion will focus less on what works at Redfield or Pierre, S.D., and more on the numerous factors which must be considered when planning rotations, why they responded the way they did, and what effect they have on input costs and profits.

Rotation: The Key to Successful No-till

For the sake of this discussion, crop production practices will be lumped into one of three broad categories Tillage, Rotation, and Technology. Each producer uses a different mix of these three factors to grow a crop. Each of these factors has positive aspects and negative ones. The key is finding the right combination for each situation. Take the nomadic tribesmen introduced previously; they used a high degree of rotation, a minimal amount of tillage, and no technology. Summer fallow systems common to the prairies at the beginning of this century employed a high degree of tillage, an intermediate amount of rotation, and almost no technology. Conventional farming systems of today utilize an intense amount of tillage, substantial technology and only minimal rotation. All of these systems successfully grew crops. When it comes to crop productivity and the factors defined above, it appears that at least two out of three are required to make a system work. This is the Rule of the Big Three: One is not enough, but 2 out of 3 isn't bad. This refers only to the requirements to consistently row a crop; outside factors such as soil erosion concerns, environmental impacts, and economics need to be considered separately.

Pioneers of no-till or zero-till recognized the benefits offered by this new technique. It saved fuel, prevented soil erosion, and furnished habitat for wildlife. But more importantly it conserved water. Prairie farmers were quick to recognize the value of this concept. Finally, they could produce a wheat crop every year without the hassle and expense of fallowing. Unfortunately they had not been taught the Rule of the Big Three. Technology, no matter how intense, was not enough to consistently cover for a lack of both tillage and rotation. Certainly, there are cases of wheat being successful grown several years in a row using no-till; but just as certainly the prairies are littered with the carcasses of crop failure that resulted when lady luck didn't choose to favor a continuously no-tilled crop. More often than not, the unfortunate producers, and especially their neighbors (also unaware of the RULE), placed the blame on the use of no-till. They were right, in that situation, no-till should not have been used. Unfortunately most did not realize that lack of rotation could just as correctly been named the culprit. Each case like this that occurs is passed from neighbor to neighbor and father to son as warning to avoid the use of no-till.

No-till pioneers, both farmers and researchers, are not to be chastised for these mistakes. It is through mistakes that learning occurs. Everyone had become a little arrogant about the wonders that technology could work forgetting to pay proper respect to the help being received from tillage. Failures forced no-tillers to dig deeper and look harder for the answers needed to take advantage of the increased moisture provided by no-till. What was discovered was rotation, the oldest concept of crop production.

By now you have probably noticed the term rotation has been used exclusively by itself rather than as it is usually found in conjunction with the word crop. This has been by design, since crop rotation is only one type of rotation that must be planned into a complete no-till system. Granted it is probably the most important factor, since it determines what you have to sell. Flexibility in the types of crops you grow and the relative acreage’s of each is limited to a certain extent by geography, climate, soils, government policy, and other factors beyond your direct control. Crop rotation, therefore becomes the logical starting point in planning your program.

The following are a series of steps similar to what is done in planning rotations for the land at Redfield and Pierre. A few of the steps have been modified to better reflect a farmer’s situation. The first procedure needed is to write down the crops allowed to be grown and the maximum number of acres of each which can be produced within the limits established by government policy. This list should include all the crops allowed, not just the ones grown at the present time. Review this list and cross off any crops that are totally unsuited to the local environment. In other words, a producer three hours north of Swan River, Manitoba could probably feel safe in crossing off cotton and peanuts. Divide the remaining list into two smaller lists. One should contain all the crops that are grown now, have been grown in the past, are grown in the area, or that have been considered as a possibility (don't forget to put maximum acreage’s on this list too). The remaining crops should be put on the second list. Now begin to differentiate the crops on list one. Leave one column blank for future use and make a column denoting whether they are a grass crop or a broadleaf. Make another column describing whether they are n annual, biannual, perennial, or winter annual in growth habit. Make another denoting normal seeding time i.e. early spring, late spring, early fall, late fall. The next column should denote normal harvest time. List the effective rooting depth of the crop in the next column. The next column should contain the height of stubble normally remaining following harvest. The next should describe the amount and nature of the stubble i.e. heavy and course, light and fine, etc Make another column denoting the minimum and recommended rotation interval for each crop (years before it should be grown again). No number 1's should occur in this column.

Using the list just compiled make a new list of potential crop rotations. Some should be familiar, similar to ones used now or in the past; others should be more daring. Try to vary the properties of succeeding crops as much as possible i.e. grass should follow a broadleaf, a high water user follows low water users, summer annuals follow winter annuals. Make a few rotations that contain only high and only low water use crops. Go through this list eliminating any rotations that have cropping intervals shorter than those recommended. Study the list for crop sequences which could produce devastating disease or insect outbreaks (in many areas wheat and barley should never follow corn because of the threat of head scab). Don't be afraid to seek assistance from the extension service or private consultants.

Once you have pared the list down to size begin using a separate sheet of paper for each potential rotation. List each crop in the rotation in one column. Put the total available water (soil water plus in season precipitation) needed to produce your yield goal for each crop in the next column. This is a difficult number to quantify accurately and only locally generated data should be used. Bear in mind that for any given year the amount of yield per inch of water will vary dramatically. There are two methods commonly used to arrive at water use efficiency numbers: the threshold concept and straight response curve. Most recent work uses the threshold idea. This approach attempts to find the amount of moisture needed to produce the first few bushels of yield and then measures the amount of increase each additional inch of moisture with produce. This probably is a better system, but a much harder one to find useful numbers for since it has not been used as long. A scientist by the name of John Cole averaged result from 15 research centers in the spring wheat production areas of the great plains and found that "on average" (those words again) about 8 inches of moisture (stored or from rain) was required for spring wheat to produce grain. Each additional inch of moisture increased yields 2.2 Bu/acre. This number is about twice as high as the 1.3 Bu/acre/inch number cited by other scientists using a straight response curve in the same area. Remember however they credit all moisture while Dr. Cole uses only that in excess of 8 inches.

Often times, when normal precipitation values are used, the final results are not too different. Using the numbers, 17 in. of available water (soil storage + in season rainfall) should produce (17 x 1.3) 22 Bu. of spring wheat per acre according to the straight-line method. Using the threshold method the predicted yield would be (9 x 2.2) 20bu/acre. Fairly good agreement! The methods do not agree as well at extremes (7 in. and 30 in. produce results of 0 and 9 and 49 and 39bu/a for these methods). The need to use local data results from the fact that in a cooler climate, where water requirements are less, the yield produced per inch of water is much greater. Data from Saskatchewan states that 10.5 inches of soil water plus precipitation will produce 14 bushels of wheat and that 6 bushels are gained for each inch after that. Using their data would result in predicting (6.5 x 6 +14) 53 bushels of wheat with the same 17 inches of water. Table 3 denotes the straight response curve value used to plan rotations at Redfield.

Once a water use requirement formula has been determined for each crop, obtain local weather records showing normal precipitation by month. Using the normal harvest data information already written down, calculate the amount of precipitation received from the time the previous crop has ceased to use water (2 - 4 weeks prior to harvest) until the succeeding crop quits using water. Label this column "Precipitation Available". Immediately eliminate any rotations, which contain crops that do not receive enough moisture in a "normal" year to produce a harvestable crop. A harvestable crop is defined as having sufficient yield to pay twice the harvesting and transportation costs.

Straight Line Response Method

	Yield per inch of water	"Average" Yield Goal Bu. or ton/acre	Water use inches
Corn	6.0 Bu.	100	16.7
Soybeans	2.2	37	16.7
Oats	5.3	70	13.0
Barley	4.6	60	13.0
Rye	3.0	49	13.0
Flax	1.8	23	13.0
Sorg.	5.8	97	16.7
W. Wheat	3.1	40	13.0
S. Wheat	2.5	32	13.0
Alfalfa	0.14 ton	2.6	18.5
Hay	0.12	2.2	18.5

Label the next column "water available for storage". This is the amount of water received between cessation of water use in the previous crop and the time the present crop begins to use a substantial amount of water. This water must be stored in order to be useful so we will use this value later in examining a soil’s suitably for a particular rotation. For spring seeded crops total precipitation from 2 to 4 weeks prior to harvest of one crop until 4 week after seeding the next is generally used. Obviously a crop like winter wheat will not use significant water until the spring after it is seeded. Situations, which leave little or no stubble (soybeans, fallow with no trap strips) should receive little credit for snowfall. Crop with stubble should receive credit based on stubble height, architecture, and snowfall characteristics in the area. A good reference for this is an article written by Steppuhn, Austenson, and Dyck in the 1987 Mandak Zero Till Conference Proceedings. At Redfield it is assumed the one-half of the November and March precipitation will fall as rain and one-half as snow. All precipitation in Dec-Feb. is considered to be snow. Credit of up to1.5 inches of water per foot of stubble height (1.3 mm per cm) is given if sufficient snow will occur.

The next column should contain normal precipitation during the crop season. Label it "crop season water". The next column is labeled "water needed from storage'. This is calculated by subtracting "crop season water' from the amount of water required to produce an average crop. Analyze any rotations that require more water from storage than there is water available for storage in a normal year. Evaluate if improving snow catch could mitigate this situation. Table 4 contains examples of these sheets for a Corn-Soybean-Spring Wheat-Winter Wheat rotation.

Lay these lists aside for awhile and take out the soil maps for all your fields. For each major soil determine the depth to a root-restricting layer, if any are present and the available water holding capacity per foot. If no restrictions occur, use 6 ft. (the SCS, PFRA, or extension service has these maps and data; sand, silty clay and loam will hold approximately 1, 1.5 and 2.0 in/ft). Multiply root zone depth by water holding capacity to determine the total water holding capacity of each soil. If the soils in a field vary little in total water holding capacity, use the value associated with the predominant soil. If the soils in a field vary widely in available water holding capacity attempt to divide the field in a manner that will segregate the soils as much as possible. If the field cannot be split in a reasonable manner, use the water holding capacity of the predominant soil, if there is one. Otherwise use the lower of the predominant soils. Make a list with all of you field’s designations in one column arranged in order of total water holding capacity (to 6 ft.). Make columns showing the actual water holding capacity of the soil if the crop has 3, 4 and 6 ft. rooting depths.

Compare your "water list" to the sheets containing your rotations. Some fields may not have sufficient water holding capacity to store moisture for certain crops even if a proper rotational sequence is followed. For each rotation list the fields (or soil types) where the available water holding capacity is equal or greater than the amount of "water required from storage" for all of the crops in the rotation. Be sure to use the appropriate crop rooting depth when comparing storage needed to storage available. Producers farming sandy or shallow soils may discover that there are few, if any, rotations where the soil is capable of holding sufficient water to produce an average crop in a normal year. Rotations requiring the least amount of water storage should be assigned to these fields. No factor has been included to account for runoff that does not enter the soil. Under a proper continuous no-till system with good earthworm activity little or no runoff will occur. This topic will be addressed later.

You now have a list of potential rotation for each field that should be relatively safe from devastating disease and insect posts, and have sufficient water to produce at least an average crop yield goal in a normal year. That does not mean these rotations are all created equal, some will produce more income, some will require less input cost, and some will fit your land, equipment, labor and government program better than others. They need a closer look.

For each field make a table similar to Tables 5 through 7 using the appropriate water holding capacity of the soil and every rotation that is applicable to that soil. For each crop in each rotation calculate the total water available in a normal year. This would be the sum of "crop season water" and the smaller of either "water available for storage" or "available water capacity" (for the soil in this field to normal rooting depth of the crop). The degree to which total water available in a normal year exceeds that required to grow an average crop is your safety factor or insurance. Calculate (using your locally developed crop response equations) the yield you would expect to receive from each crop in a normal year. This will not be the same as "Average crop yield goal" since the amount of soil moisture storage will vary with rotation, stubble height, rotation interval, etc.

This is sufficient data to get you started but a little more information can prove quite valuable. Calculate expected yield for each crop, field, and rotation using 50% and 150% normal precipitation. You must do each component separately since soil moisture storage will be more efficient in a dry year and less efficient in a wet one. Everyone does crop budgets based on an average year; this lets you plan for drought and floods also.

A few examples using diverse rotations and soil types will be made. The rotations are Spring Wheat-Barley, Spring wheat-Soybeans, Corn-Soybeans, Spring Wheat-Corn-Soybeans, Corn-Barley- Winter Wheat, Corn-Fallow-Winter Wheat, and Spring Wheat-Winter Wheat. The soils are a coarse sand having a water holding capacity of 1 in/ft, three feet deep over gravel, a deep silt loam with a water holding capacity of 1.8 in/ft and a deep silt loam with a water holding capacity 2.6 in/ft. The sand could provide 3 in. of water for all crops; the first silt loam 5.4 in. to small grain and 7.2 in to corn and soybeans, and the second silt loam 7.8 in to small grain and 10.4 in to corn and soybeans. Spring cereals are seeded April 1, begin using water May 1, and cease water use July15. Corn and soybeans begin water use June 1st and quit September 1.

Winter wheat begins May 1 and ceases use July 1. A brief summary is helpful in making the necessary calculations.

Rainfall since last crop - Total precipitation received as rain (not snow) in the interval between when the previous crop ceased using water and the present crop began using water. One half of November and one half of March precipitation was assumed to be rain, the remainder snow.

Snow Credit - Water equivalent of snow catch calculated assuming 1.5 in. of water for each foot of stubble height or total snowfall whichever is less.

Rainfall since last crop - Total precipitation received as rain (not snow) in the interval between when the previous crop ceased using water and the present crop began using water. One half of November and one half of March precipitation was assumed to be rain, the remainder snow.

Snow Credit - Water equivalent of snow catch calculated assuming 1.5 in. of water for each foot of stubble height or total snowfall whichever is less.

Rainfall since last crop - Total precipitation received as rain (not snow) in the interval between when the previous crop ceased using water and the present crop began using water. One half of November and one half of March precipitation was assumed to be rain, the remainder snow.

Snow Credit - Water equivalent of snow catch calculated assuming 1.5 in. of water for each foot of stubble height or total snowfall whichever is less.

Construction of tables such as this represents a substantial amount of work, but they will pay for the time spent many times over. A word of caution should be included here. In calculating predicted yields no attempt has been made to adjust for differences due to disease, weed, or insect pressure, etc. In reality rotations such as the spring wheat-winter wheat combination may exhibit substantially lower yield due to these considerations. In fact, such a rotation probably should not have made the "first cut" when those having potential disease problems were eliminated. It is included to make just such a point later on.

In reviewing the soil moisture data and predicted yields contained in Tables 5-7 several expected and unexpected results occur. Some points concerning comparisons of no-till and conventional tillage practices need to be made. It is quite evident and expected that the soil's ability to store water is a primary limiting factor to crop yields in normal and wet years even on the soils having an available water holding capacity of 1.8 and 2.6 in/ft. The surprising result of this analysis is that in a good share of the rotations soil water holding capacity is also a primary limiting factor in normal to dry years, especially on the two soils having lower water holding capacity. Most comparisons and evaluations of no-till vs. conventional tillage have been done using rotations common to conventional tillage situations. In many of these rotations there is sufficient water, even in dry years, to allow 2 to 4 inches to be wasted through the use of tillage and still allow the soil to be full at seeding time. Unless these trials are done on sites having sufficient slope and for a long enough period of time to allow runoff to play a role, very little difference in yield would be expected. Most research to date has been one on relatively level ground for periods of only a few years. This can be likened to comparing the ability of a world class weightlifter and the local banker by having them lift a 20 pound barbell. There would be no significant differences found. If the contest were made more challenging by increasing the weight 20 fold the differences become evident. The above analysis and actual results from Redfield (to be shown later) demonstrate that high water use rotations such as corn-soybeans can be successfully and profitably grown no-till in an environment where they are not considered viable options for conventional tillage systems.

The last remarks to be made about water deal with a subject that has only recently surfaced to any great extent in North America, earthworms. No attempt was made in calculating water relation data to adjust for runoff losses. The reason for this is quite simple. In the Redfield environment several years of continuous no-till leads to a tremendous increase in earthworm activity in the soil. The burrows which they form have increased the infiltration capacity these "tight' soils to the point that they will not produce any runoff even if 6 inches of rain is received in 15 minutes. They will take 40 inches of rain in 3 hours also with no runoff. If any tillage is performed that cuts these burrows the soil can only accept about 2 inches of water in a three-hour period. It is obvious that as long as no tillage is performed, runoff is no longer a factor that needs to be considered. Dr. Bill Edwards who works with runoff and erosion for the USDA-ARS has produced dramatic and well documented data demonstrating similar effects where runoff was eliminated from a no-till field planted on a slope of greater than 20% that produces no runoff in a 40 inch per year rainfall area.

Most of the work with earthworms and their effects on the soil has been done in Europe, Australia and New Zealand. It indicates that an active population of earthworms not only increases water infiltration rates, but also incorporates residue and fertilizers into the soil. They are Mother Nature’s plow according to Charles Darwin who wrote a book on earthworms. There is also an indication that they can improve soil aeration and increase the available water holding capacity of a soil by at least 30%. After reviewing this literature it is of little surprise that many researchers and producers have been finding increased advantages and decreasing management problems with no-till as the number of years the system has been used increases. The experience of Redfield indicates that the problems of saturated surface soils at seeding time often cited as a primary problem for no-till, occurs only until sufficient macropores are present to move excess water deeper into the soil where it is protected from evaporative losses and does not interfere with field operations. Excessively heavy residue and the resulting allopathic effects it can have are also reduced after a period of years. It is felt that the positive effects of earthworms may be one of the most important keys to successful no-till programs. Consequently a graduate research assistant has been assigned to evaluate some of the factors affecting present earthworm populations in both no-till and conventionally tilled fields and developing ways to introduce them in situations where they have not occurred previously or have been eliminated by numerous years of tillage.

The common misconception that inorganic fertilizers and herbicides kill earthworms is not substantiated in the research that has been done. Inorganic fertilizers increase earthworm populations. Farmyard manure has a greater positive effect since it has both plant residues and nutrients. Herbicides in general have no negative effect. Certain insecticides, fungicides and soil fumigants are toxic to earthworms. One of the biggest detriments to surface feeding species is tillage, which disturbs their burrows, buries their food, and exposes the soil to wider fluctuations in moisture and temperature. This fact was easily demonstrated to interested visitors at Redfield by easily digging hundreds of worms in the no-till herbicide demonstration plots and subsequently being unable to fund any in an adjacent conventionally tilled field.

The single most important factor involving earthworms for producers on the prairies is their ability to eliminate runoff. Close behind however is the less well-documented potential they have for increasing available soil water holding capacity by 30% or more. The effect this will have on yield can easily be demonstrated by adjusting the soil water column in Table 5 – 7 upward then recalculating yields. In all but the driest years, yields will be increased substantially.

One calculation that is valuable for evaluating rotations will be called Precipitation Use Efficiency. This number is obtained by expressing the Total Water Available as a percentage of Total Precipitation. It is away of comparing soils and rotations for their ability to use the most valuable commodity on the prairies (or the buffalo commons), moisture. Calculations for the soils and rotations in Tables 5-7 are listed in Table 8.