Agricultural Sustainable Production in Vulnerable Zones to Nitrate Pollution

Abstract

WHO (World Health Organization) stablishes an illustrative threshold for nitrates in drinkable water of 50 mg L^-1. In order to reach this objective, Council Directive 91/676/EEC indicates that countries should define vulnerable zones, which are or could be affected by high nitrate levels and eutrophication. The aim of this research is to determine different fertilization treatments impact on yield and quality for two legume crops cultivated in a rotation system in vulnerable zones to nitrate pollution of La Rioja, northern Spain. Four fertilizing treatments were tested in two commercial plots for two years. One of them was the control treatment usually performed by the farmer, and the other treatments were designed to reduce N fertilization requirements looking to increase crop sustainability. Moreover, N amount in soil, in plant were measured weighing crop biomass and yield to analyse the effect of fertilizing treatment. Furthermore, harvest quality was assessed specifically for each crop such as tenderness for pea or seed to pod ratio for green bean. Each crop was monitored using Sentinel-2 satellite imagery and UAV multispectral imagery acquired during crop development. Results showed no significant differences between treatments in pea, whose yield varied from 9.4 ± 0.4 t ha^-1 to 13.4 ± 0.9 t ha^-1. Tenderness degree showed a bit high values which oscillated from 85 ± 4 to 122 ± 10. Green bean crop provided larger but scattered yield values which changed from 6.6 ± 2.9 t ha^-1 to 18.2 ± 3.6 t ha^-1. Seed to pod ratio showed slight but opposed differences to yield varying from 2.8 ± 0.4 % to 6.0 ± 3.4 %. In conclusion, legume crops will be over fertilized even if nitrogen application is reduced between 59.6 % to 86.3 % during a one-year rotation.