Strategies to improve nitrogen use efficiency in winter cereal crops under rainfed conditions
Developing fertilizer strategies that increase nitrogen use efficiency (NUE) could reduce unnecessary input costs to farmers and environmental impact of N losses. Two field experiments were performed in northern Spain to evaluate alternative N fertilization strategies to improve NUE in winter cereal crops (wheat [Triticum aestivum L.] and barley [Hordeum vulgare L.]). The strategies were: (i) adjusting the fertilizer rate by soil mineral N before N application; (ii) splitting of N fertilizer application; and (iii) the use of fertilizer with a nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP). The experiments were designed as a completely randomized block design with seven treatments and four replications. Treatments included a control, two single applications, one with DMPP, and four split N applications. Nitrogen balance was calculated according to the general equation of conservation of mass for any soil–crop system from which N-efficiency parameters were determined. Grain yield followed a quadratic-plus-plateau model with different optimum N rate depending on the year (71 and 98 kg N ha–1 in 2002–2003 and 2003–2004, respectively). Adjusting N fertilizer rate by soil mineral N before N application gave a maximum yield and a similar NUE to the optimum N rate predicted by the model. Neither applying N in two doses nor including a nitrification inhibitor with a single dose showed any advantages in terms of yield or N efficiency.