Nitrogen fertilization strategies for organic wheat production: Crop yield and nitrate leaching

Nitrogen fertility management represents a crucial aspect for common wheat (Triticum aestivum L.) production, particularly when we deal with organic agriculture. This study was conducted to determine the effect of five N fertilization strategies on yield, grain protein content, and N leaching risk. In a 3-yr field experiment, a faba bean/wheat temporary intercropping (TIC) and four fertilization treatments with extra-farm N sources were compared. Extra-farm N sources were represented by blood meal (BM) and roasted leather (RL) (broadcast all-at-once at seeding or split into one-half at seeding and one-half at tillering in a side-dressing application). Unfertilized and mineral fertilized controls were included. The effect of the legume on TIC wheat N uptake was always positive while dry weight accumulation and yield were generally poorly affected. Regardless of the broadcasting method, BM treatments generally showed a slightly higher yield and grain protein content compared to wheat fertilized with roasted leather (this was also confirmed by fertilizer release efficiency). The risk of N leaching was maximum at the onset of drainage (i.e., during the first phase of crop growth), so using organic fertilizers at preseeding stage appeared to be a very risky practice, especially if quick-N-releasing ones are used. Splitting the organic fertilizer rate avoided a large amount of mineralized N to be leached in the watershed during the critical stage of drainage onset. The TIC was the best option in terms of environmental preservation, and assured a constantly higher grain protein content compared to the other organic fertilization treatments.