Kansas Crop Residue Removal and Effects on Crop Yield and Soil Sustainability

By Keith A. Janssen and David A. Whitney Kansas studies emphasize the importance of crop residues and adequate soil fertility in maintaining yields and soil organic matter levels.

CROP RESIDUES are being consid­ percent slope) Woodson silt loam soil ered as a source of raw materials for var­ included residue treatments begun in the ious non-agricultural uses. But crop fall of 1980 and continued for 12 consecu­ residues also are needed for surface soil tive years using a --grain cover and to replenish soil organic matter. sorghum cropping sequence. Only one crop was grown each year. Residue treat­ Many grain producers currently ments were: 1) residue removed each year crop residues for feed or other after grain harvest; 2) normal crop residue farm uses with little noticeable negative incorporated; and 3) twice normal residue effects. Generally, this is not done on an incorporated. Fertilizer treatments listed every year basis from the same field. Also, in Table 1 . . . zero, low, normal and high some of these plant materials may be levels of N-P-K for the three crops . . . returned to the field as animal wastes. The were superimposed on residue treatments. potential for influencing crop and soil sus­ tainability could be much greater with non-agricultural crop residue uses. Table 1. N-P-K fertilizer treatments for crops in rotation. The first concern when crop residues Fertilizer Soybean Wheat Grain sorghum are removed is with soil erosion protection treatments N-P205-K20,lb/A and whether conservation compliance will Zero 0-0-0 0-0-0 0-0-0 be jeopardized. Residue removal can also Low 0-0-0 25-15-25 50-15-25 affect soil water conservation and storage. Normal 0-0-0 50-30-50 100-30-50 Residue removal can deplete plant nutri­ High 0-0-0 75-45-75 150-45-75 ents, deplete soil organic matter, and change soil physical properties. The effects of fertilizer management in offset­ Grain yields and residue yields were ting plant losses when crop resi­ measured each year. Soil samples (0 to dues are removed is not well understood. 6-inch depth) were collected after the 11th year for chemical analysis. Soil bulk den­ sity measurements were also performed Kansas Study on the 0 to 4-inch depth. A disk-field culti­ This study was established to deter­ vate system was used for seedbed mine the effects of returning varying preparation and residue incorporation levels of crop residue on crop yields and all years. soil properties in a soybean-wheat-grain sorghum rotation, fertilized with variable The Results rates of nitrogen (N), (P) and (K). Grain yields and residue yields varied with crop and year. Soybean yields The study at the East Central Kansas ranged from 14 to 53 bu/A, residue yields Experiment Field on a nearly level (0 to 1 ranged from 0.34 to 0.81 tons/A; wheat

Dr. Janssen is Associate Professor and Dr. Whitney is Professor, Dept. of , Kansas State University, Manhattan, KS 66506-5501.

4 Better Crops/Vol. 79 (1995, No. 2) 150 140 130 120 Fertilizer Treatment 110 — Zero 100 -- Low 90 80 Normal ' 70 -High SI 60 ,::-"\ if 50 40 30 20 10 0 '81 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 Year Figure 1. Effects of fertilizer applications on grain yield. yields ranged from 29 to 50 bu/A, resi­ due yields from 0.99 to 1.47 tons/A; and grain sorghum yields ranged from 54 to 129 bu/A, residue yields from 1.11 to 2.66 tons/A. Crop residue yields, like those of grain, vary substantially with growing season. Although direct residue produc­ tion comparisons are not valid because all crops were not grown in the same year, grain sorghum produced the highest overall average amount of residue, 1.69 tons/A, wheat 1.20 tons/A, and soybean 0.57 tons/A.

The residue treatments caused no statis­ tically significant differences in grain yield for any crop in any year. Neither the removal of crop residue nor the adding

4 INCREASED crop residues result from better fer­ 3.5 tilization practices and higher yields. The Fertilizer Treatment O - benefits are better erosion control, increased O To — Zero soil organic matter and improved moisture o 2.5 - - - Low infiltration. 2 Normal //

yield , of twice normal crop residue influenced 1.5 - crop yield. 1 Fertilizer increased both grain and resi­ Residu e due yields, shown in Figures 1 and 2. 0.5 Generally, highest grain and residue 0 '—i—i—i—i—i—i—i—i— yields were produced with the normal and '81 '82 '83 '84 '85 '86 '87 '88 '89 '90 '91 '92 high fertilizer treatments. Year Soil analyses after 11 years of residue- Figure 2. Effects of fertilizer applications on fertilizer treatments indicated significant residue yield. differences in exchangeable K, bulk

Better Crops/Vol. 79 (1995, No. 2) 5 Fertilizer Level Fertilizer Level

Removed Normal 2X Normal Residue treatment Residue treatment

Figure 3. Soil exchangeable K after 11 years of Figure 4. Soil organic matter after 11 years of residue and fertilizer treatments. residue and fertilizer treatments. density (data not shown), and organic mat­ Summary ter due to residue treatments. There was The results of this study suggest that in a statistically significant interaction situations where soil erosion and soil between the residue and fertilizer treat­ water relations are of little concern, ments for exchangeable K, Figure 3. removal of crop residues should not affect Exchangeable K was affected most by crop yield over the short term. Removal of the residue treatments. Exchangeable K crop residue will, however, slightly lower decreased when crop residue was removed. soil organic matter and will increase soil Doubling crop residue increased exchange­ bulk density compared to normal residue able K, especially when higher levels of K incorporation. These slowly occurring fertilizer were applied. This was because effects are potentially long-term serious the high K content of the residue plus the factors. Removal of crop residue will fertilizer K exceeded crop K removals. require application of extra K in the rela­ Soil organic matter decreased with crop tively short term because of the high K residue removal and with normal residue content of residues. incorporated when no fertilizer was Long-term, continuous residue removal applied, Figure 4. Doubling crop residue remains questionable. That's because increased soil organic matter. Doubling long-term removal could cause further crop residue in combination with high fer­ decline in soil organic matter, increased tility produced the most residue and the soil physical problems and eventually highest soil organic matter levels. Organic affect crop yield. matter in the soil is a result of the balance In different environments with different between loss from decomposition and soils, the effects of removing crop resi­ gain from crop residues and roots due could be much different. This soil returned to the soil. Soil bulk density was initially high in soil organic matter increased slightly with removal of crop for the area and had medium to high levels residue and decreased slightly with doub­ of soil fertility. Soils with lower organic ling of crop residue. This is likely a reflec­ matter and lower fertility would likely tion of the differences in soil organic be affected more quickly by crop residue matter levels. removal. •

Better Crops/Vol. 79 (1995, No. 2)