Spring Cover Crop Management Options for Dryland Crop Productions Systems
Background
Cropping system diversification with cover crops can provide several benefits. These include improving soil quality, nutrient cycling, weeds and pest suppression, and reduce wind erosion. Cover crop adoption is not widely popular in water-limited environments because cover crops utilize water that otherwise would be available to the subsequent cash crop. Grazing or haying CCs can provide economic benefits to compensate for potential revenue loss associated with decreased crop yields when CCs are grown ahead of wheat or grain sorghum.
Research Objectives
Research Objectives
- Determine forage production potential of cover crop mixtures.
- Investigate the impacts of removing cover crops for forage on soil water content, subsequent crop yields, and soil health.
- Evaluate flex-fallow as a strategy for integrating cover crops into semiarid environments.
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Methods
Field experiments compared summer-fallow to grazing or haying CC, and growing CC solely for cover in the fallow phase of a wheat-sorghum-fallow crop rotation system. Main plots were three crop phases of a wheat-sorghum-fallow, and sub-plots were ten CC treatments of single, two-, three-, and six-species mixtures of oat, triticale, peas, radish, turnips, and buckwheat compared to chemical-fallow. The CCs were planted in the spring of the fallow phase of the rotation. In addition, a flex-cover crop treatment was included and planted to CC only when soil moisture levels are adequate and the precipitation outlook is favorable. This treatment was left fallow when available soil water content at CC planting is < 12 in., and summer and fall precipitation outlook is not favorable. The flex-cover crop treatment was implemented only in 2018 when conditions were met (less soil water content and precipitation outlook was unfavorable). Generally, grazing and haying of CCs occurred at heading. The CCs were terminated by the third week in June with glyphosate and 2, 4-D in 2015. Paraquat and Aim EC were used to terminate CCs in 2016 through 2019. Soil samples were taken to determine bulk density and soil water content at winter wheat planting, and were measured at 3 ft in 2015 and at 5 ft in subsequent years of the study (2016 through 2019). In 2019, soil samples were taken at 0 to 2 inches and 2 to 6 inches after CC termination to determine soil organic carbon (SOC) concentration. Winter wheat and sorghum grain yields were determined by harvesting a 5-ft × 100-ft area from the center of each plot using a small plot combine.
Results
Forage Mass and NUTRITIVE Value
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Forage DM produced varied over the five years because of variations in soil water availability and air temperature in the spring. Forage mass ranged from 2225 lb/a for the cocktail treatment to 3026 lb/a for oat/triticale mixture or spring triticale alone. This result suggests decreasing the proportion of grass species in the mixture tends to reduce the amount of forage biomass produced (Table 1). |
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Figure 1. Forage mass as influenced by year and cover crop management at the Kansas State University experiment fields at HB Ranch near Brownell, KS. Bars followed by the same letter (s) are not significantly different (P < 0.05).
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Oat/triticale CC forage mass was greatest in 2015 (3145 lb/a) and least in 2019 (1655 lb/a, Figure 1). The lower CC forage mass production in 2019 was due to wetter than normal spring conditions that delayed cover crop planting until late April. Similarly, a cold and dry spring in 2016 resulted in less CC productivity. In years with limited regrowth (2016, 2017 and 2018), CC forage mass at the time of grazing was similar to ungrazed (cover) CC treatment. The hay treatment was harvested at a greater height (6 inches) and therefore had relatively lower yields than cover treatments (clipped at 2 inches). In 2015 and 2019 when there was time for regrowth before CC termination, biomass left after grazing was similar to that measured pregrazing (Figure 1).
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Excluding 2019, which had more post-grazed biomass than pregrazing, residue left post-grazing across the four remaining years (2015 through 2018) averaged 68% of that at pregrazing. Therefore, careful grazing of CCs can leave adequate amount of residue to protect the soil to achieve soil health goals while providing a forage resource for livestock.
Forage CP concentration and IVDMD were greater when peas were included in the mixture compared to mixtures with only grass species (Table 1). Similarly, ADF and NDF concentrations were lower for the three-way (oat/triticale/pea) and cocktail compared to oat or triticale alone, and oat/triticale mixture. Nonetheless, in a production setting, grazing of forage would likely begin at a more immature stage of forage growth and the quality would match the needs of stocker cattle.
Soil Bulk Density and Soil Organic Carbon
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Figure 2. Cover crop management effect on soil bulk density (a) measured from fall 2015 to 2018 and soil organic carbon (b) measured in 2019 at the Kansas State University experiment fields at HB Ranch near Brownell, KS. Bars followed by the same letter (s) are not significantly different (P < 0.05).
In general, except in 2015, growing a CC had no effect on soil bulk density measured at 0 to 2 inches at winter wheat planting. Grazing a CC in 2015 resulted in a significant increase in soil bulk density at 0 to 2 inches (Figure 2a).This was because of a significant precipitation event ( > 3 inches of rainfall) that occurred during grazing. No difference in bulk density was observed beyond the top 2 inches over the study period. The SOC concentration measured in 2019 was not different due to treatments at the surface 0 to 2 inch soil depth. However, the CC treatments did increase SOC concentration within 2 to 6 inch depth (Figure 2b) compared to fallow. The SOC concentration with haying or grazing CCs was similar to that of the true cover treatment, suggesting belowground biomass from CC roots contributes to SOC storage. This short-term study showed CCs could be utilized for forage with minimal impacts on SOC.
Winter Wheat and Grain Sorghum Yield
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Figure 3. Cover crop management effect on winter wheat grain yield (a) and grain sorghum yield (b) over the study period at the Kansas State University experiment fields at HB Ranch near Brownell, KS. Bars followed by the same letter (s) are not significantly different (P < 0.05).
Winter wheat yields after CCs were not significantly affected in 2016 and 2018 (Figure 3a). However, a significant decrease in winter wheat yield was observed in 2017 and 2019 when CCs were grown ahead of wheat (Figure 3a). Averaged across the 5 years, wheat yields averaged 41.8 bu/a with CC treatments and 51.9 bu/a with fallow, representing a 10 bu/a decrease in wheat yields when a CC was planted ahead of wheat. In general, CC management had no effect on sorghum grain yield in this study. Across years, sorghum grain yield ranged from 70.1 bu/a with the hayed treatment to 77.0 bu/a when CC was grazed.
Over this 5 year study, haying or grazing a CC had no significant effect on wheat or sorghum yields compared to yields when CC was left as cover (Figures 3a and 3b). This finding suggests CC could be utilized for forage with similar impact on subsequent crop yields compared to when grown as a true CC. This is significant because utilizing CC for forage (grazing or haying) will generate income to compensate for revenue loss associated with decreased crop yields when CCs are grown ahead of a cash crop.
Over this 5 year study, haying or grazing a CC had no significant effect on wheat or sorghum yields compared to yields when CC was left as cover (Figures 3a and 3b). This finding suggests CC could be utilized for forage with similar impact on subsequent crop yields compared to when grown as a true CC. This is significant because utilizing CC for forage (grazing or haying) will generate income to compensate for revenue loss associated with decreased crop yields when CCs are grown ahead of a cash crop.
Figure 4. Average cover crop and weed biomass measured in June 2016 and 2017 at Kansas State University experiment fields located the HB Ranch near Brownell, KS.
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Another thing worth mentioning is potential savings in herbicide application costs from growing CCs. In this study, CC biomass resulted in > 95% suppression of total weed biomass relative to the weedy-fallow check. Weed biomass ranged from as low as 4 lb/a with oat/triticale or oat/triticale/pea to 680 lb/a for the weedy-fallow (Figure 4). Approximately three to four herbicide applications were done to control weeds in chem-fallow treatment compared to two herbicide applications in the CC treatments (termination of CCs and another burndown prior to wheat planting).
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