Effects of Wheat-Residue Management on Double-Cropped Soybean and Subsequent Crops

Management of wheat (Triticum aestivum L.) residue is an important consideration in production of double-cropped soybean [Glycine max (L.) Merr.]; however, little information is available concerning long-term effects of wheat-residue management on subsequent crop yield and soil quality. A 12-yr study was conducted in southeastern Kansas to evaluate the agronomic effects of three wheat-residue management practices (moldboard plow, burn then disk, and disk only) on: (i) grain yield, seed weight, and leaf nutrient concentrations (N,P,K) of double-cropped and full-season soybean and winter wheat in a 2-yr cropping rotation; (ii) soil moisture and bulk density at the R5 soybean growth stage; and (iii) changes in soil fertility properties (pH, organic matter [OM], P, and K). Double-cropped soybean yield varied with wheat-residue management and available soil moisture, but no residue practice was superior in all years. Seed weight and leaf K concentration of double-cropped soybean were highest with plowing, whereas disking resulted in greater soil bulk density, regardless of year. Grain yield, seed weight, and leaf N, P, and K concentrations of subsequent full-season soybean and winter wheat were not affected significantly by previous wheat residue management. After six 2-yr cropping cycles, soil pH, OM, available P, and exchangeable K had changed very little from initial values. In rotations where double-cropping occurs only once every 2 or 3 yr, wheat-residue management may not have significant long-term effects on subsequent crop yield or soil quality. Research QuestionIn the eastern Great Plains, double-cropped soybean typically is planted every 2 or 3 yr, depending on the frequency of wheat in the cropping rotation. Management of wheat residue becomes an important factor in successfully establishing double-cropped soybean; however, little information is available concerning long-term effects of wheat-residue management on subsequent crop yield and soil quality. The objectives of this 12-yr study were to evaluate the agronomic effects of three wheat-residue management practices (moldboard plow, burn then disk, and disk only) on: (i) grain yield, seed weight, and leaf N, P, and K concentrations of double-cropped and full-season soybean and winter wheat; (ii) soil moisture and bulk density at the R5 soybean growth stage; and (iii) changes in selected soil chemical properties (pH, organic matter, P, and K). Literature SummaryIn the southern USA, researchers have evaluated the effect of various wheat-residue management practices on yield of double-cropped soybean and on soil properties. Higher economic returns have been reported for burning wheat residue followed by no-till planting. However, burning of residue is controversial. Short-term economic benefits and labor saving may be offset by long-term detriment to soil quality. Long-term effects of burning crop residue generally have been reported only in continuous-wheat producing regions. Leaving wheat residue near the soil surface with disk tillage or planting no-till reduces soil erosion and increases water conservation, although soybean root growth may be reduced because of greater soil compaction compared with incorporating residue. Wheat straw also has been shown to inhibit growth of double-cropped soybean by allelopathy. Effects of wheat-residue management on subsequent crop growth have been mixed. In Georgia, plowing or chiseling before double-cropped soybean resulted in significantly higher wheat yields than with no tillage; however, in Mississippi, wheat yields were unaffected by previous management practices for tillage or straw. Research is limited on the long-term effects of wheat-residue management on yield, nutrient uptake, and soil quality. Study DescriptionField studies were conducted at the Kansas State University Southeast Agricultural Research Center (Columbus Unit) from 1982 to 1995. Soil was a Parsons silt loam consisting of a shallow topsoil (12 in.) overlying a thick “claypan” subsoil. The experimental design was a randomized complete block with three replications. Wheat-residue treatments prior to planting double- cropped soybean were: (i) moldboard plow (6 in.), disk, field cultivate; (ii) burn stubble, disk, field cultivate; and (iii) disk tillage only, which consisted of one pass with a heavy tandem disk and two passes with a lighter tandem disk. Individual plot size was 40 by 150 ft. Wheat-residue treatments were evaluated each year by alternating the 2-yr rotation of wheat-double-crop soybean followed by full-season soybean in two adjacent sites. All plots were chiseled in the spring prior to planting full-season soybean. In the fall, all plots were disked before drilling wheat. Wheat-residue treatments were imposed on the same plots in each year of the study, and six complete cropping cycles (12-yr) were evaluated at each site. Applied QuestionsWhat effect did wheat-residue management have on double-cropped soybean productian? Grain yields varied with wheat-residue management, but no residue practice was superior in all years. Plowing residue under produced significantly higher yield in 4 yr, whereas leaving residue near the soil surface by disking gave the highest yields in 3 yr. In 3 of 11 yr, grain yield was not affected significantly by residue treatments. On average, the plow system had yields of 23.2 bu/acre, which was 2.4 and 1.8 bu/acre more than the burn-disk or the disk only treatment. However, this slight yield increase from plowing residue under would not offset the additional cost of the tillage system based upon custom tillage costs and current soybean prices. Seed weight and leaf K concentration of double-cropped soybean were significantly higher with plowing, whereas soil bulk density was greater with disking, regardless of year. Results suggest that tillage, rather than a burning regime, had a greater effect on K uptake, which also appeared to affect soybean seed weight. Although soil moisture content was significantly affected by wheat residue management, differences between treatments generally were not large and did not fully explain why grain yields varied with residue management in certain years and not in others. Were subsequent crops in the rotation affected by previous wheat-residue management practices? Grain yield, seed weight, and leaf N, P, and K concentrations of subsequent full-season soybean (first year) and winter wheat (second year) were not affected significantly by previous wheat-residue management. Spring chiseling prior to planting full-season soybean apparently eliminated any potential compaction zones resulting from previous plow or disk residue-management treatments and from fall harvesting equipment. Did wheat-residue management have any long-term effects on soil properties? Soil pH, organic. matter, available P, and exchangeable K had changed very little from initial values after six 2-yr cropping cycles, except for some redistribution of P and K into the 6- to 12- in. depth when soil was plowed. What are the implications of this research for the wheat-double-cropped soybean systems in the eastern Great Plains? In rotations where double-cropping occurs only once every 2 or 3 yr, which is typical in the eastern Great Plains, any particular wheat-residue management practice probably will not have significant long-term effects on subsequent grain yield or soil quality. However, our results do not address the environmental impact of wheat-residue management on soil and water conservation or air pollution in double-cropped soybean production systems. In addition, improved equipment technology has made no-till planting of double-crop soybean more feasible than when this study was established. Thus, no-till planting of double-crop soybean has been adopted by many producers in recent years. However, regardless of whether wheat stubble is shallowly incorporated by disk tillage or left on the soil surface (no-till), the long-term effects on soil properties probably would be similar in crop rotations where soil is chiseled the following spring prior to planting a summer crop.