In dryland production in western Kansas, the factor that most limits crop yield is water availability. No-till summer crops capitalize on the moisture saving nature of high-residue levels. Typically the best corn is grown following wheat, Kansas’ highest residue producing crop. Strip-till reduces residue levels in the tilled strip, exposing soil to the air. How will this affect the overall water balance for crop production? Research in the panhandle of Texas might provide information on this subject.
In an intensively monitored research plot, where soil water contents were measured to 10 feet, and soil evaporation rates were measured daily using micro-lysimeters, estimates of seasonal evaporation were determined for cotton grown in two tillage systems. Table 3 shows that total evaporation from both systems were similar, but that a greater percentage of water transpired through the plant where residue was retained in the strip-till system. This 37 percent increase in transpiration efficiency resulted in a 35 percent increase in lint yield.
click image to zoom At the end of the season, in an arid or semiarid environment, water added as precipitation or as irrigation will likely end up in the atmosphere from the large and ever-present evaporative demand. Management of the soil will dictate how that water travels to the atmosphere. In this environment, increasing the amount of water that moves through the plant typically leads to higher yields. Maintaining higher residue, whether through strip-till management or through no-till management should increase yield potential in western Kansas.
Soil Organic Carbon in the Balance
Soil productivity is strongly tied to soil organic matter and microbial activity. Many researchers have shown how tillage intensity reduces soil organic matter. The most intense tillage practice involves using a moldboard plow, and as data from Sydney, Nebraska shows (Table 4) all tillage practices result in a reduction of soil organic matter from that of native sod. The greatest loss occurs with the most aggressive tillage system. Total soil nitrogen also follows this trend with tillage. Even though producers provide most of the nitrogen needed for crop production through fertilizer nitrogen applications, the ability of the soil microbiological community to hold that nitrogen and release it to a growing crop is an important factor. In their study, Follet and Schimel showed that increased tillage intensity decreased the soil’s capacity to immobilize and conserve mineral nitrogen.
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