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a USDA-ARS, Northern Great Plains Research Lab., Box 0459, Mandan, ND 58554-0459
b Univ. of Mary, 7500 University Dr., Bismarck, ND 58504
* Corresponding author (krupinsj{at}mandan.ars.usda.gov)
Received for publication April 24, 2006.
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: RUSLE, revised universal soil loss equation • RWEQ, revised wind erosion equation • SLR, soil loss ratio
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Crop residue coverage protects soil and land resources from erosion, conserves soil water, maintains soil quality, and influences the soil surface environment. Retention of crop residues on the soil surface has a significant effect on soil quality. Crop residues left on the soil surface result in increased soil organic C (Liebig et al., 2005), improved soil physical properties (Arshad et al., 1999; Pikul and Aase, 1995), and enhanced microbial activity and biomass (Liebig et al., 2006). Such changes in near-surface soil condition improve the functioning of cropping systems through increased water storage (Deibert et al., 1986; Tanaka and Anderson, 1997), reduced soil erosion (Merrill et al., 1999), and improved nutrient conservation (Follett and Schimel, 1989). Collectively, improvements in soil condition through the retention of crop residues on the soil surface increase the resilience of Great Plains cropping systems to droughts, wet periods, intense precipitation events, and extreme temperatures, all of which are common to the region (Peterson, 1996).
Moisture retention is improved with crop residue coverage because of reduced evaporation, increased snow trapping, and reduced surface runoff due to better water infiltration (Cook and Veseth, 1991; Lal, 1995). By promoting water infiltration and by insulating the soil surface, moderating the soil temperature and limiting evaporation, crop residue coverage modifies the microenvironment (Dormaar and Carefoot, 1996). By modifying the microenvironment, residue may influence the development of the subsequent crop. Although results varied with site and year, wheat residue reduced plant establishment, plant biomass, and yield of canola in New South Wales (Bruce et al., 2005). Similarly, wheat residue influenced the stage of development and height of corn (Zea mays L.) in 2 out of 3 yr in Michigan (Kravchenko and Thelen, 2005). Residue management practices can contribute to the suppression of some soilborne plant diseases, but understanding the mechanisms involved is limited (Bailey and Lazarovits, 2003). Crop residue contributes to increasing soil microbial activity and so increases the likelihood of competition among organisms in the soil (Bailey and Lazarovits, 2003). Reduced tillage practices may also favor some plant pathogens by lowering soil temperature, increasing soil moisture, and leaving the residue and soil undistributed (Bockus and Shroyer, 1998). Another possible concern with crop residues is allelopathy, as chemicals released by residue may have deleterious affects on crop growth. In a review of wheat yield responses to conservation practices, Kirkegaard (1995) summarized that allelopathic effects of residue are poorly understood.
Rainfall simulation and wind tunnel technology have shown a relationship between residue coverage of soil and water and wind erosion (Bilbro and Fryrear, 1994; Laflen and Colvin, 1981; Foster et al., 1982). Information on the impact of crop residue on erosion is embedded in USDA-ARS empirical, user-oriented models, such as the revised universal soil loss equation (RUSLE) model (Renard et al., 1997) for water erosion and the revised wind erosion equation (RWEQ) model (Fryrear et al., 1998) for wind erosion. Another model providing information on the interaction of crop residues with other erosion-affecting factors is the wind erosion prediction system (WEPS) model (Hagen, 1991). Much of the information about crop residue coverage effects on erosion and associated residue decay in these models derives from southern or mid-U.S. sources.
Merrill et al. (2006) have reported on the effects of different crop species on crop residue coverage of soil in an earlier crop sequence project. More testing with new and emerging crops and crop sequences, and environmental conditions will help further the understanding of crop sequence effects on crop residue coverage of soil. The objective of this project was to determine the influence of additional crops and crop sequencing on crop residue coverage of soil under the semiarid environmental conditions of the northern Great Plains.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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6.1 ha each, were located 2 km apart. Predominant soils at the sites are Temvik–Wilton silt loams (fine-silty, mixed, superactive, frigid Typic and Pachic Haplustolls). Long-term annual precipitation averages 409 mm, with 79% of the total received during the growing season from April through September. Annual temperature averages 4°C, though daily averages range from 21°C in the summer to –11°C in the winter. During the research project, monthly precipitation and air temperature varied during the growing season (Fig. 1
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Nitrogen was applied as a mid-row (between every other row) band application of NH4NO3 at 78 N kg ha–1 during seeding except for chickpea, dry pea, or lentil. Phosphorus was applied with the seed as 0–44–0 at 11 kg P ha–1 during the seeding of all crops. Sulfur was applied as ammonium sulfate during the seeding of canola at 11.2 kg S ha–1 and N source adjusted to obtain 78 kg N ha–1. Recommended inoculants were applied to dry pea, lentil, and chickpea seed before seeding. Weed control was accomplished using no-till techniques appropriate for each crop.
Crop Residue Production
Crop residue production data from Project Year 2 (Table 1) were obtained to show the amount of crop residue produced. Crop residue production was determined at physiological maturity by hand clipping all aboveground biomass from 0.35 m2 (0.57 by 0.61 m). Samples were air dried for about 1 mo, oven dried at 60°C for 48 h, and weighed to determine total biomass. Samples were threshed, grain was cleaned and weighed, and grain was subtracted from the total biomass to get residue production. Crop residue production data from Project Year 1 was reported (Tanaka et al., 2007).
Crop Residue Coverage of Soil (Surface Residue Coverage)
All measurements of crop residue coverage of soil were done after spring wheat was direct-seeded into crop residue from the previous growing season. Crop residue coverage of soil was measured with a transect technique (Tanaka and Hofman, 1994). Counts of residue presence on the soil surface were taken at 25 points equally spaced along a 7.6-m cable, which was stretched across a plot to count the number of residue contacts. On each plot, a double-transect diagonal sampling pattern (V) was used, which pointed in the same direction of seeding. When residue intersected with a point on the cable, it was counted as a contact. The total number of residue contacts was recorded. During Project Years 1 and 2, two double transect V patterns (for 100 points) were used for each plot. Because of the number of plots (100 plots x 4 replicates) for all crop sequence combinations evaluated during Project Year 3, one double transect V pattern (for 50 points) was used. When 50-count and 100-count data were compared at Site 1 in 2004, similar results were obtained for the 100 plots evaluated. Plots were evaluated after seeding and before crop emergence.
In Project Year 1 (Table 1), surface residue coverage from the previous 2 yr of spring wheat was measured after spring wheat was seeded to obtain an overall estimate of background crop residue coverage for the project. Surface residue coverage was measured in every other plot, (five plots per rep, total of 20 plots) at the time of seeding spring wheat.
In Project Year 2 (Table 1), surface residue coverage was measured in all plots seeded to spring wheat. This was done to determine the amount of crop residue coverage of soil provided by each of the 10 crops after only 1 yr.
In Project Year 3 (Table 1), at the time spring wheat was seeded over the crop matrix, surface residue coverage was measured for all plots to determine crop residue coverage of soil following the 100 crop sequences present in the crop matrix (four replicates).
Three subsets of Project Year 3 data were selected and analyzed for additional insights: (i) The first subset included nine treatments with an alternative crop for 1 yr (spring wheat, Project Year 1/alternative crop, Project Year 2/spring wheat, Project Year 3; e.g., spring wheat/canola/spring wheat) plus the continuous spring wheat treatment. These treatments were measured after seeding spring wheat to determine the amount of surface residue coverage provided by each of the 10 crops after only 1 yr, similar to the Project Year 2 data. (ii) The second subset included nine treatments with the same alternative crop for 2 yr (alternative crop, Project Year 1/same alternative crop, Project Year 2/spring wheat, Project Year 3; e.g., canola/canola/spring wheat) plus the continuous spring wheat treatment. These treatments provided a more homogeneous crop residue by reducing the carryover of residue from another crop species. They were measured to determine the amount of residue coverage provided by each of the 10 crops after 2 yr of the same crop. (iii) The third subset included 36 crop sequence combinations of six crops, three crops that provided higher surface residue coverage the subsequent year (proso millet, grain sorghum, and spring wheat), and three crops that provided lower surface residue coverage the subsequent year (lentil, chickpea, and sunflower). This subset was analyzed to compare sequence combinations of crops that provide a range of surface residue coverage [lower (first year of crop sequence)/lower (second year of crop sequence), lower/higher, higher/lower, and higher/higher, e.g., nine crop sequence combinations of lentil, chickpea, and sunflower, nine crop sequence combinations of proso millet, grain sorghum, and spring wheat.]
Residue Coverage and Erosion
The soil erosion hazards of the lowest residue coverage values measured can be evaluated by applying algorithms dealing with flat residue coverage that are contained in empirical erosion models: the RWEQ model (Fryrear et al., 1998) and the RUSLE model (Renard et al., 1997). Equations in the models predict soil loss ratio (SLR) values directly from residue coverage values. The SLR is defined as the ratio of soil loss with residue present to soil loss that would occur without residue under conditions in which other soil factors are in a state of relatively high soil erodibility, such as a dry, smooth soil surface with low soil aggregation. Thus, SLR = 1 with no residue present, and SLR = 0 with complete residue coverage. Wind-erodible soils have smooth surfaces with low slope, while water-erodible soils are sloped.
Statistical Analysis
Data for crop residue production and crop residue coverage of soil were analyzed using the general linear model procedure (SAS Institute, 2003). Statistical comparisons for each evaluation were made with Student-Newman-Keuls' test and Dunnett's one-tailed test. Dunnett's one-tailed test was used to make comparisons between crop sequence treatments and the continuous spring wheat treatment, which was used as a control. Statistical differences were evaluated at the probability level of P < 0.05. Probability level of P < 0.01 was also used to compare surface residue coverage after 99 crop sequences to the continuous spring wheat treatment.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Surface Residue Coverage after Alternative Crop for One Year (Spring Wheat/Alternative Crop)
During the establishment of each crop matrix (Project Year 2), crop residue coverage was evaluated soon after seeding spring wheat. The crop residue coverage after seeding spring wheat averaged 88% at Site 1 and 72% at Site 2. At Site 1, higher residue coverage followed proso millet, grain sorghum, spring wheat, corn, canola, and buckwheat and lower crop residue coverage followed chickpea and lentils (Fig. 2A
). At Site 2, higher residue coverage followed spring wheat and proso millet (Fig. 2B) and lower residue coverage followed sunflower and corn. Thus, surface residue coverage was differentially impacted by the previous alternative crop. One can speculate that the plant biomass production and carryover of crop residues varied among alternative crops impacting the surface residue coverage the following spring.
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Crop Residue Production
Crop residue production data from Project Year 2 (Table 1) were obtained for all 100 crop sequence treatments in the crop matrix. Overall, the amount of crop residue returned to the soil surface varied among second-year crops of the crop sequences (Tables 2 and 3, bottom row). At Site 1 (2003), the highest average crop residue production was measured after grain sorghum, followed by proso millet, sunflower, and spring wheat (Table 2, bottom row). At Site 2 (2004), the highest average crop residue production was measured after corn and sunflower (Table 3, bottom row). When evaluating the overall carryover effect of the first-year crop of the sequence (Table 2 and 3, right column) differences were not evident at both sites. At Site 1 (2003), the highest average crop residue production was measured after dry pea, followed by canola, lentil, chickpea, and spring wheat (Table 2, right column). This may be related to soil water available to the second-year crop in the sequence. For example, dry pea, when present as a first-year crop in the sequence, would use the least soil water of the crops grown, leaving more available for the second-year crop in the sequence, whereas sunflower, when used as a first-year crop in the sequence, a higher soil water user of the crops grown, would leave less soil water available for the second-year crop in the sequence (Merrill et al., 2007). At Site 2 (2004), no carryover effect from the crop used in the first year of the sequence was evident (Table 3, right column).
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Surface Residue Coverage after Crop Matrix
In Project Year 3 (Table 1), at the time of spring wheat seeding, crop residue coverage of soil was obtained for all 100 crop sequence treatments in the crop matrix. Differences in surface residue coverage were evident among second-year crops of the crop sequences (Tables 4 and 5, bottom row). The highest average residue coverage was measured following spring wheat, proso millet and grain sorghum at both sites. At Site 1, the lowest residue coverage was measured after sunflower and corn, followed by chickpea, lentil, and dry pea (Table 4, bottom row). At Site 2, the lowest residue coverage was measured after sunflower, followed by lentil, chickpea, dry pea, and then corn (Table 5, bottom row).
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The carryover effects of the 10 first-year crops were also compared when data for each second-year crop were analyzed individually. The carryover effect of the first-year crop in the crop sequence was more evident with crops which provide lower levels of surface residue coverage than with crops which provide higher levels of surface residue coverage (Tables 4 and 5, individual crop columns, excluding the bottom row). For example, almost no differences were detected with spring wheat, proso millet, and grain sorghum (data columns 8, 9, and 10), crops which provide higher levels of surface residue coverage. With these three crops, the amount of surface residue coverage of the second-year crop had an overriding influence on surface residue coverage with almost no obvious carryover effect from the first-year crop in the crop sequence. For second-year crops which provide lesser amounts of surface residue coverage, crop residue coverage of soil tended to be higher following a first-year crop that produces a higher level of surface residue coverage. This is consistent with the recommendation that crops producing higher levels of residue be grown before crops producing lower levels of residue especially on more fragile soils (Merrill et al., 2006). Besides the variation in the amount of residue produced by a particular crop, the rate of residue decomposition may have varied (Soon and Arshad, 2002).
Spring wheat, canola, dry pea, and sunflower were common to the present crop sequence project and an earlier crop sequence project (Krupinsky et al., 2006). The surface residue coverage values observed in the two projects may be compared by aggregating crop sequences and taking 2-yr averages of surface residue coverage values measured following the crop matrix phase (Project Year 3) in 2000 and 2001 (Fig. 3 in Merrill et al., 2006) and in 2004 and 2005 (Table 6). The present crop sequence project was performed during years which had below-average annual precipitation (Fig. 1), while the earlier crop sequence project was performed in years with above-average precipitation (Fig. 2 in Krupinsky et al., 2006). The greater availability of moisture during the earlier project may have led to greater decay of residues (Stott et al., 1986; Summerell and Burgess, 1989) in crop sequences with dry pea and sunflower and may possibly have been the reason that there was lower average surface residue coverage of the soil for these sequences than in the present project (Table 6). However, surface residue coverage values for sequences with spring wheat in the first year and sunflower or dry pea in the second had similar values in both experiments, and sequences with spring wheat, canola, or both crops had higher surface residue coverage values in the earlier project than in the present project.
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Selected Surface Residue Coverage Treatments (Spring Wheat/Alternate Crop) after Crop Matrix
The first subset of Project Year 3 data included nine treatments with an alternative crop for 1 yr (spring wheat/alternative crop/spring wheat) plus the continuous spring wheat treatment. Treatments were analyzed to evaluate the surface residue coverage after an alternative crop for one growing season. Crop residue coverage of soil was similar for both sites, with an average of 80% coverage at Site 1 and 83% at Site 2. Higher levels of crop residue coverage of soil were associated with previous spring wheat, grain sorghum, proso millet, buckwheat, and canola crops at both sites (Fig. 3A and 3B). Lower levels of crop residue coverage of soil were observed after lentil, chickpea, and sunflower at both sites. Thus, crops varied in their impact on surface residue coverage when measured the next spring at the time of seeding a subsequent spring wheat crop. This is consistent with results presented above when the same crop sequence treatments were evaluated soon after seeding spring wheat in Project Year 2 when the crop matrix was established.
Selected Surface Residue Coverage Treatments (Alternate Crop/Same Alternate Crop) after Crop Matrix
The second subset of Project Year 3 data included nine treatments with the same alternative crop for 2 yr (alternative crop/same alternative crop/spring wheat) plus the continuous spring wheat treatment. Treatments were analyzed to evaluate the surface residue coverage after growing the same crop for 2 yr. Crop residue coverage averaged 77% at Site 1 and 73% at Site 2. The crops varied in their impact on crop residue coverage of soil. Higher levels of surface residue coverage were associated with previous spring wheat, grain sorghum, and proso millet crops at both sites (Fig. 3C and 3D). Lower levels of surface residue coverage were observed after sunflower, lentil, chickpea, corn, and canola at both sites. There is a tendency for surface residue coverage following two seasons of crops that provide lower crop residue coverage of soil to be lesser than surface residue coverage following one season of the same crop.
Selected Surface Residue Coverage Treatments (Crops Associated with Low and High Residue Coverage) after Crop Matrix
The third subset of Project Year 3 data included crop residue coverage associated with three crops that provide higher crop residue coverage of the soil the subsequent year (proso millet, grain sorghum, and spring wheat) and three crops that provide lower crop residue coverage of the soil the subsequent year (lentil, chickpea, and sunflower). Treatments were analyzed to compare various combinations of surface residue coverage (lower/lower, lower/higher, high/lower, and higher/higher). The surface residue coverage ranged from 65% for the lower/lower combination to 93% for the higher/higher combination in 2004, and from 56 to 94% in 2005, respectively (Fig. 4
). Consistent with results presented above, two seasons of crops which provide lower crop residue coverage of soil provide significantly less surface residue coverage than other combinations. This supports studies that have shown potentially greater soil erosion when crops which provide lower crop residue coverage of soil are grown in succession (Merrill et al., 2006).
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Even with the practice of no-till, the use of sequences with crops such as sunflower and pulse legumes such as dry pea for two consecutive years can result in lack of adequate residue coverage and heightened soil erosion risks under drought conditions. Lack of precipitation at critical times can result in reduced crop stands and lack of adequate crop growth, and subsequently inadequate surface residue coverage. During drought periods, inadequate crop growth and consequent low residue presence will negatively synergize with soil erodibility factors to increase wind erosion risks (Merrill et al., 1999). Inadequate precipitation and stored soil water can lead to a decision to summer fallow in dryland cropping areas. Most likely the greatest erosion hazard in cropping systems occurs if tillage and/or summer fallowing are practiced after a lower-residue crop. Merrill et al. (2004) measured the wind erosion of a silt loam soil on no-till-managed sunflower stubble land (sunflower following spring wheat), which was subjected to various degrees of spring tillage treatments (no-till, medium-till, and heavy tillage [conventional]) followed by chemical (glyphosate) summer fallowing. The combination of tillage and chemical weed control under relative summer dryness resulted in unacceptably high levels of wind erosion. Even the no-till treatment had moderately elevated measured levels of soil loss under a high-energy windstorm event (Merrill et al., 2004).
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Sustainable management of dynamic cropping systems requires that producers base crop sequencing on the principles of adaptability, diversity, environmental awareness, information awareness, multiple enterprises, and reduced input costs (Tanaka et al., 2002). We have shown that certain crops produce lesser amounts of residue or tend to have less durable residues. Two-year sequences with higher-residue crops like spring wheat in the first year produce greater residue coverage than sequences with 2 yr of lower-residue crops. A first-year crop of spring wheat, proso millet, or grain sorghum can provide sufficient residues in a sequence where the next crop is low-residue (or rapidly decomposable). A producer operating on more fragile soil and concerned about reducing soil erosion hazards would be advised to grow higher-residue crops in the year before such species as dry pea or sunflower.
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ACKNOWLEDGMENTS |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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