Optimization of Nitrogen released and immobilization from soil-applied prunings of Sesbania sesban and maize stover

Abstract

A glasshouse experiment was conducted using the double-pot technique involving mixtures of low and high quality N sources with the objectives of determining 1) N mineralization and substitution value of high quality organic materials, 2) N immobilization by low quality maize stover, and the subsequent remineralization of immobilized N, and 3) N mineralization from or immobilization by mixtures of high and low quality organic materials. The experiment was designed in a 6 x 3 factorial combinations of sources of easily available N (inorganic fertilizer and Sesbania sesban) with a source of low level of available N (maize stover). The six levels of easily available N were 0, 50, 100 and 150 mg N per pot in the form of NH4NO3-N, and about 34 and 136 mg organic N per pot with S. sesban prunings. The levels of maize stover were 0, 2.5 and 5.0 g per pot. Application of 2.5 and 5 g maize reduced maize biomass yield by 4 and 16%, and N immobilization by 18-24% of added equivalent fertilizer N at 28 days after sowing (DAS), and 22% at 49 DAS. The decline of immobilized N at 42 and 49 DAS for the 2.5 g stover was ascribed to remineralization of N immobilized earlier. From the results of N uptake, the substitution value recovered was between 0.23 and 0.41 for S. sesban. Application of low quality organic materials (maize stover) in combination with high quality organic materials has shown initial immobilization of inorganic N that has been mineralized by the high quality organic materials and is slowly remineralized later.