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SWEEP Report #46

Management of Farm Field Variability. IV. Crop Yield, Tillage System, and Soil Landform Relationships

Researchers: 
R.G. Kachanoski and M. H. Miller, Department of Land Resource Science, Centre for Soil and Water Conservation, University of Guelph, Guelph, Ont.; J.D. Aspinall, Resources Management Branch, Ontario Ministry of Agriculture and Food, Guelph, Ont.; A.P. von Bertoldi, Department of Land Resource Science, University of Guelph, Guelph, Ont.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

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Associated SWEEP/LSP Research

 

 

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Completed: May, 1992

Key Words:

conventional tillage, conservation tillage, moldboard plow, minimum tillage, no-till, corn, soybeans, small grains, yield, soil texture, landscape position, Tillage 2000

Executive Summary

This report documents the last two objectives of the SWEEP/TED project "Management of Farm Field Variability". The objectives of this part of the project were to determine crop yield response to different tillage systems, at different landscape positions, and relate the variations in crop yield response to soil and landform properties. The possibility of implementing variable management was examined by quantifying the stability of the yield response pattern over a number of years.

The study was carried out in cooperation with the provincial Tillage-2000 project, which is a cooperative project of the Ontario Ministry of Agriculture and Food (OMAF), the Dept. of Land Resource Science (Univ. of Guelph), and cooperating farmers. Details of the study are given in the annual reports of the project, which are available from OMAF.

Field sites were selected from the existing Tillage-2000 sites for detailed examination of the relationships between landform, soil properties, soil loss, tillage management, and crop yield. At each field site, two tillage systems (conventional, conservation) had been established and permanent benchmark monitoring locations selected. The conservation system was defined as any tillage system which should decrease the loss of soil from the field by erosion. The tillage system were classified as no-till if no primary or secondary tillage was completed, minimum till systems if no inversion tillage (moldboard plough) system was used and moldboard if a moldboard plough was used to invert the soil.

Landform at each benchmark was characterised by carrying out a detailed elevation survey using a laser theodolite, and calculating parameters based on a digital elevation model and classification system. The landform classification is based on the slope gradient and change in slope gradient with distance (curvature) at a location. A concave surface with low slope is classified as a footslope while a convex surface with low slope is a crest/shoulder position. In addition the cross-slope curvature can be causing water to converge (concave cross-slope) or diverge (convex cross-slope) at a point and landforms are further divided by this classification.

Relative soil loss was obtained from relative changes in 137Cs content (a naturally occurring soil tracer) measurements. Soil properties were obtained from a 1.0 m soil core taken at each site using a hydraulic soil sampler. Yield measurements collected as part of the Tillage-2000 program were entered into the data base containing all of the other information. Soil sampling for soil fertility analysis was also completed. Indices for plant-available water and air filled porosity were calculated from soil profile data. The objective of the sampling program was to obtain as complete a database as possible. A copy of the database accompanies this report.

The 5 year (1986-1990) average grain corn, soybean, and small grain yields in the paired conservation and conventional tillage systems were not significantly different. In addition, field- by-field, and year-to-year differences in yield were equally variable in the conservation and conventional systems. The paired moldboard and minimum tillage sites suggested a slight yield advantage to the moldboard system. Average relative crop yields across all crop types were higher in the moldboard system for all years except 1988. A total of 23 out of 36 plot years had higher yields on the moldboard system compared to the minimum tillage system.

The paired no-till and moldboard tillage sites indicated no significant difference in yield for any of the crop types. A total of 14 out of 23 plot-years had a higher yield in the no-till system than in the moldboard system. Average relative yield across all crops was higher in 1987 and 1988 in the no-till compared to moldboard, but lower in the other three years.

The paired no-till and minimum tillage sites indicated a slight yield advantage to the no-till system. The average no-till yield was significantly higher than minimum tillage yield (0.1 probability) for both the soybeans and small grain crops.

Conservation tillage systems, both overall and in the paired tillage comparisons, did relatively better than conventional systems in 1988 (a drought stress year) than in any other year. This suggests that conservation tillage systems are more buffered against adverse crop growth conditions than conventional systems.

Soil texture (Ap horizon) class and tillage texture class interactions were significant (0.001 probability) in explaining the variations in yield of all crop types. Landform class was significant for corn and soybeans, but not small grains. A regression of the ratio of no-till yield/conventional tillage yield against % sand content of the Ap horizon was significant (0.05 probability). The regression indicated that for % sand contents greater than 36% the no-till yield would on average be higher than the conventional tillage system. The no-till yield for finer textured soils would on average be lower than conventional tillage systems. The interaction of tillage and texture is suggested as the reason for little overall differences in tillage system on crop yield, across all farm sites.

Landform classification criteria as proposed by Pennock and de Jong (1987) are not sensitive enough at the elevation measurement scale used in this study (i.e. 10 m grid). The criteria for backslope versus level class (6.5% slope) resulted in an unacceptably large number of level class designations. The criteria was changed to 3% slope gradient.

A general analysis of covariance confirmed the presence of significant covariance between the major soil properties. The 7 unit landform classification system was not very useful in explaining variations in soil properties. This was partly attributed to the high variability of texture within the landform classes, and the covariance of texture and other soil properties.

A sub-classification by upper, middle, and lower slope position within each of the original landform classes explained a significant (0.05 probability) amount of the variability of almost all soil properties, especially those related to soil loss. The conceptual model of the slope location of the original landform classes was correct for approximately 60-70% of the benchmarks. However, a significant number of benchmarks were found at slope positions not conforming to the conceptual model. The poor success of the original 7 landform classes in explaining the spatial variations of soil properties was attributed to the conflicting patterns that water flow and tillage translocation would have on soil properties.

Solum depth was significantly related to soil texture class, but 137Cs content was not related to texture. This suggests that the amount of soil loss is not related to texture, and the increased solum depths in the sandy soils are related to pedogenic processes. The independence of soil loss on soil texture, and the higher cesium loss on upper slope compared to middle slope positions are contrary to water erosion theory, but consistent with tillage translocation theory.

The difference between the highest and lowest yielding areas in a field, across all years and all sites was 40% of the mean field yield. Tillage system did not significantly affect the within field variations in yields. The lowest, highest, and range, of relative yield difference were similar in the paired tillage comparisons. The standard deviation of relative yield difference was slightly higher (0.05 probability) in the minimum compared to no-till system.

The percentage of within field variation of yield remained constant from year to year was on average 52% and 56% (significantly different at 0.10 probability), for the conventional and conservation tillage systems respectively. Approximately 3% of the benchmarks had an average yield which was at least 30% less than the average field yield. Another 5% of the benchmarks were between 20% and 30% lower than the field average yield. A total of 15%, and 4% of the benchmarks had an average yield which were greater than 10%, and greater than 20% of the field average yield respectively. The relative ranking of the benchmarks with respect to relative yield was independent of the measurement year, but the year did affect the magnitude in all yield classes. The drought stress year (1988) resulted in much greater relative within field variations of crop yield.

A paired benchmark analysis on crop response on stress (low yielding) and non-stress (high yielding) benchmarks, in stress and non-stress growing conditions was carried out. It indicated that conservation tillage systems may be more buffered against adverse climatic growing conditions than conventional tillage systems. High yielding areas under conservation tillage dropped only 13.8% in yield during a stress year, compared to 16.5% decrease in the conventional system. Low yielding areas in the conservation system decreased 24% in yield in the stress year, compared to a 31.1% decrease in the conventional system. This benchmark data supported the paired field yield data, which indicated that the ratio of conservation yield/conventional yield was the highest in 1988 the drought stress year.

The 7 unit landform classification explained a significant amount of the within field benchmark yield data. Converging landforms had on average 8.5%, 7.8%, and 5.5% higher yields of corn, soybeans, and small grains respectively, compared to diverging landforms. Across all crop types the average difference between converging and diverging landforms was 7.3% (significant at 0.05 probability level). The diverging shoulder and backslope position had significantly lower corn and soybean yields, than the other landform units.

There was a significant interaction of soil texture class and soil loss, on relative crop yield losses. Benchmarks were separated on the basis of % sand in the Ap horizon and yield response correlated against cesium content in each texture class. Yield response to soil loss was predicted from these correlations. Severely eroded soils with a % sand content greater than 70% had an average predicted yield loss of 37% of the field average yield. The same severely eroded soils had a predicted yield loss of only 8.0%, 4.7%, and 0.7% for Ap horizons with 50-70%, 40-50%, and 30-40% sand content. The yield loss in all texture groupings increased during the 1988 growing season indicating soil loss was affecting available water, but more so in the sandier soils. The available water index of McBride and Mackintosh (1984) was significantly related to cesium content in the > 70% sand content group, but not in the other groups. The benchmarks with 20-30%, and < 20% sand content had a predicted relative yield decrease of 4.3% and 8.0% respectively. Thus, the benchmarks in the medium texture classes had much less predicted yield loss from soil loss, than benchmarks with lighter or finer soil textures. This is consistent with the higher available water holding capabilities of medium textured soils compared to other textures.

The data in this project, and in the Tillage-2000 project indicate that it should be possible to implement a conservation tillage system with no loss in yield productivity. This is especially true for sandy textured soils where increases in yield are likely under conservation tillage.

For the range in soil and landform conditions in this report, there seems to be little benefit to adopting a minimum tillage system. No-till yields were equal or better than minimum till and the minimum till was slightly lower yielding than the moldboard tillage. In addition, the work on tillage translocation suggests that secondary tillage, which can sometimes be more intensive under minimum tillage, can result in significant soil loss off of shoulder/crest slope positions. The criteria of 20% or 30% residue cover to control water erosion is meaningless with regards to tillage translocation. Thus, unless a management procedure can be devised to control tillage translocation, minimum tillage can not be viewed as a viable alternative to a moldboard system in a sustainable production system. The minimum till system may control water and soil loss by water erosion, but it will not be stopping the decline in soil quality and crop productivity in the upland regions.

The study indicates that the sandy soils (> 70% sand) are the most fragile of all of the soil types. Soil loss in upper convex slope positions has already resulted in yield losses of 30-40% of the average field yield. The productivity losses are even more severe in years of climatic stress. However, since on average these soils had a higher yield in no-till than in any other tillage system, there seems little reason for farmers not to adopt the no-till system immediately. The main mechanism of soil loss is tillage translocation, and water erosion is likely to be minimal considering the high infiltration capacities of sandy soils.

Conservation tillage systems appear to be increasing the soil's buffering capacity against adverse climatic conditions, particularly drought stress. This is encouraging considering the possibility of increased frequencies of drought stress due to global warming trends. The full extent of the remediating capabilities of no-till is not very well understood and should be the subject of future studies. The remediation may appear to be faster than expected because the massive soil loss from tillage translocation has been stopped in the no-till, but continued in the conventional tillage system. Thus, even if the yield productivity of severely degraded areas is stabilized, it would appear that they have undergone an increase because of the continued decline in productivity of the conventional system. The actual rate of remediation, and degree to which it is possible to remediate these areas is unknown, and beyond the scope of this study.

A considerable amount of research activity is currently underway regarding variable management. A symposium on this subject will be held at the annual American Society of Agronomy meeting. Other symposia have been held the past few years by the American Society of Agricultural Engineers (ASAE). Most of the activity has centred on development of spatial location sensors, and variable application technology. There seems to be little doubt that the technical ability to vary management within the field will be present; the important missing link is the knowledge base to decide what kind of management should be done at each point in the field. The yield data indicates that reasonably consistent pattern of yield are present year after year. Thus, variable management from a cost benefit point of view is necessary. Technology for automatic measurement and recording of yield patterns is available, but more accurate equipment is needed.

The consistent yield differences in the benchmarks from year to year is encouraging, and it is clear that many of the differences are related to soil loss or the effects of soil loss. The sites with very large yield losses are diverging shoulder slope/crest positions as indicated by Battiston et al. (1987). This problem can be attributed almost entirely to tillage translocation. The obvious solution is not to till the fields. However, it may be possible to change the pattern of tillage. The necessity of at least alternating the direction of all tillage, including secondary tillage cannot be overstated. The net soil losses from alternating tillage directions is still very large, but much smaller than the loss from a single direction.

Without an accurate method of predicting the soil redistribution from tillage translocation, there does not appear to be much hope in explaining any more than about 40-50% of the spatial variations of soil properties. The same constraint exists for predicting variations in yield response using only landform classification. The alternative is to measure and map yield response directly from year to year and identify sensitive areas from changes in yield from year to year especially during climatic stress conditions. While it is possible to predict that the areas of high yield loss will likely be the shoulder slope positions, it is not true that all shoulder slope positions have been eroded and thus will have yield reductions.

 


Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)

The study was carried out in conjunction with Tillage 2000. The objective was to: determine crop yield response to different tillage systems and different landscape positions, and relate variations in crop yield response to soil and landscape properties. In total there were 40 farm sites, on a field scale, 3 or 4 landscape units at each site. A basic soil survey was done at every site. Corn, soybeans, and small grains were studied. The tillage systems were classed into conventional and conservation. The tillage classes were further broken down into moldboard, minimum, and no-till.

The study compared the various tillage types in relation to yield response. Moldboard plow showed a slight yield advantage when compared to minimum tillage. No significant yield difference was evident between the moldboard system and no-till. The no-till system showed a slight yield advantage over the minimum till system. The study indicated that over all and in the paired comparisons the conservation systems did relatively better in the year of drought stress than did the conventional system. This suggests a buffering action of conservation tillage systems during times of water stress.

There was little difference overall in tillage systems on crop yield across all farm sites. The reason given was the interaction of tillage and texture. There was significant interaction of soil texture class and soil loss on relative crop yield losses.

Comments:

The effectiveness of tillage systems on soil conditions over time can be verified by yield comparisons. Of note is that a no-till system, when done properly, can produce yields above conventional systems on certain soil types.

Associated SWEEP/LSP Research:

  • SWEEP Report #3 - An Economic Assessment of the Distribution of Benefits Arising from Adoption of Conservation Tillage Practices in Crop Production in Southwestern Ontario
  • SWEEP Report #20 - Conservation Tillage Equipment: Availability, Utilization and Needs
  • SWEEP Report #29 - The Effect of Organic Mulches on Soil Moisture and Crop Growth
  • SWEEP Report #38 - Management of Farm Field Variability. I. Quantification of Soil Loss in Complex Topography. II. Soil Erosion Processes on Shoulder Slope Landscape Positions
  • SWEEP Report #45 - Management of Farm Field Variability. III. Effect of Tillage Systems on Soil and Phosphorus Loss
  • SWEEP Report #56 - Yield Reduction Effects of Crop Residues in Conservation Tillage
  • SWEEP Report #60 - The Effect of Conservation Tillage Practices on the Losses of Phosphorus and Herbicides in Surface and Subsurface Drainage Waters
  • SWEEP Report #66 - Volume V. Economic Assessment of the Technology Evaluation and Development (TED) Program

Future Research: ( ) indicates reviewers suggestion for priority, A - high, C - low.

See SWEEP Reports #38 & #45

 

 

 

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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 03:26:54 PM