Concurrent evaluation of agronomic and environmental aspects of nitrogen fertilization in cauliflower production

Abstract

Despite major efforts over the past 25 years to decrease nitrogen (N) losses, too high nitrate (NO3‑) concentrations in surface and groundwater from agriculture remain an important environmental concern, especially in field grown vegetable production regions. A stringent limitation of the N fertilizer application rates is accepted to be the best N management strategy to minimize NO3‑ leaching losses. We analyzed Flemish fresh market cauliflower field experiments with various N supplies (2000-2013). We examined total and marketable yield quantity and quality and residual soil mineral N (RSMN) to rooting depth (0-60 cm) at harvest in function of the N supply (= N fertilizer application rate + NO3--N in the 0-60 cm layer). The results show that the total and marketable yield quantity were negatively affected at an N supply less than 200 kg N ha‑1. Nitrogen supply had a larger effect on the score of curd color and crop stand than on leaf color and volume, curd firmness and uniformity. However, small reductions in scores of leaf and curd quality parameters resulted in a rejection of the cauliflower as high standard Flandria class, causing an economic loss. The RSMN of treatments with an N supply ≤ and >200 kg N ha‑1 was on average 56±42 and 89±82 kg NO3--N ha‑1, respectively. Optimum N supply for the earliest crops will be of the order of 200-250 kg N ha‑1, while later in the season this optimum should be reduced by at least 50 kg N ha‑1 as a consequence of higher Nmin at planting, possible N mineralization from crop residues from an earlier crop and differences in N mineralization from soil organic matter. The results indicate that N fertilizer application rates of fresh market cauliflower can be further fine-tuned combining both agronomic and environmental aspects of N fertilization.