Recovery of Residual Fertilizer-N and Cotton Residue-N by Acala and Pima Cotton.

Little is known about the availability of residual fertilizer-N and cotton (Gossypium spp.) residue-N to subsequent crops. This study determined the effects of two soil types and N fertilization rates on the recovery of residual 15N-fertilizer and 15N from labeled cotton residue in the soil and plants of subsequent cotton crops. Microplots in the San Joaquin Valley, California, on a Panoche day loam [fine-loamy, mixed (calcareous), thermic Typic Terriorthents] and a Waseo sandy loam (coarse-loamy, mixed, nonacid, thermic Typic Torriorthents) were used to trace the fate of 15N from labeled aboveground cotton residue separately from the 15N in roots and soil. Total 15N-fertilizer recovery in the second year after application averaged 5.8% for Acala (G. hirsutum L.) and 2.9% for Pima (G. barbadense L.) cotton. In the third year after application, total 15N-fertilizer recovered by Acala averaged 2.0% on the clay loam soil and 3.3% on the sandy loam. Most of this recovered 15N-fertilizer was cycled through soil pools and roots and only small amounts originated from labeled aboveground residue. Virtually all of the 15N applied in the form of labeled aboveground residue and recovered in the soil was found in the top 0.3 m. The 15N-fertilizer which cycled through belowground pools was found mainly in the top 0.6 m of the soil. Recovery of residual 15N-fertilizer appears to contribute little to total cotton N uptake in the second and third crop after application. [ABSTRACT FROM AUTHOR]