Resource conserving techniques and nitrogen use efficiency in different cropping systems

Abstract

Nitrogen (N) is the most important nutrient for cereal production. Although, the price of N fertilizers is increasing worldwide, N use efficiency is quite low. Fertilizer N recovery by the first crop in a rotation is 30–50% but the recovery by up to six consecutive crops is less than 7%. The use of resource conserving techniques for enhancing N efficiency is reviewed in this paper. No-tillage increases N losses through denitrification compared to other tillage systems. The rate of denitrification was higher in compacted areas, such as wheel tracks, compared to normal field conditions. Increasing fertilizer rate applications minimized potential yield reductions associated with implementing no-till corn production in a drier climate in silt loam soil and in a humid environment with fine textured soils, potential yield reductions minimized fertilizer N management, but tillage effect appears to be independent of N management. Deep banding N fertilizer (0.10–0.15 m deep) resulted in superior spring wheat yields compared to broadcast application under zero tillage (ZT) in semi-arid climates. The effectiveness of nitrification inhibitors (NIs) under conservation tillage depends on N placement and environmental conditions. Surface applied ammonical N treated with NIs was ineffective in reducing nitrification due to drier and warmer soil surfaces; these being ideal conditions for volatilization, whereas deep placement can reduce N losses and improve N use efficiency. N use efficiencies decreased with increasing critical values from ≤3 to 5, but it was always higher than recommended N management in rice–wheat cropping systems in different cultivars. A group of 107 farmers compared the leaf color chart (LCC) method with their own N management practices and found that the LCC reduced the N requirement from an average of 154 to 122 kg N ha-1. A net saving of 32 kg ha-1 or 25% of applied N was recorded. The general trend showed that N uptake increased with strip tillage for all growth stages compared with the no-tillage across sites and years in corn.