Sorghum stover removal and fertilizer nitrogen effects on sorghum yields and nutrient cycling

Typescript (photocopy).A four year field study was conducted to evaluate the effects of sorghum stover removal and fertilizer N on yields of four sorghum genotypes, soil properties, and nutrient cycling in a conventional tillage, continuous sorghum cropping system. Applications of 112 kg N ha⁻¹ were generally sufficient for maximum yields, fertilizer N uptake efficiency and, the greatest percentage partitioning of N, P and K uptake into grain. In some years stovers apparently acted as sinks, immobilizing and/or denitrifying N. Stover parts such as stalks and lower stover components contained high amounts of nonstructural and structural carbohydrates and had a high C:N ratio, immobilizing applied N for 9 months in a greenhouse study. The noted increase in yield variability during the latter study years, the reduced ability of fertilizer N to affect yields, and stover's positive effects on N and P cycling may have been due to cumulative adverse effects of stover removal on the soil environment. Complete stover removal reduced soil available P and K levels, and disrupted the soil organic matter (SOM) equilibrium, resulting in increased SOM decomposition and a net release of nutrients. Returning upper sorghum stover portions to fields would cycle a relatively high percentage of stover N and P, while the remaining lower two-thirds, high in carbohydrates, could be harvested for energy conversion. Interactions of sorghum genotypes, fertilizer N and stover return effects on long-term soil productivity must be delineated to determine if stover removal can become an environmentally sound and sustainable production strategy