Distribution of Mineral Nitrogen in Soil in Relation to Risk of Nitrate Leaching in Farms with Irrigated Vegetables and Early Potatoes

Abstract

Vegetable production may be the source of excessive residual nitrate that is prone to leaching to waters. To ascertain the risk of nitrate leaching in water collection area, the content of soil mineral nitrogen (Nmin = N-NO3− + N-NH4+) down to 120 cm depth was monitored in the years 2013–2016 on vegetable farms along lower Jizera river (in the Czech Republic). The risk of nitrate leaching below 30, 60, 90 and 120 cm during winter period was simulated with a simple model. The depths represent the limits of effective root depth and N depletion of groups of vegetables and field crops. The average autumn mineral nitrogen content in the fields, during experimental years, ranged from 101 kg to 134 kg N·ha−1 in the 0–120 cm soil layer, 85 to 92% of which was in the form of nitrate. The calculated leaching of nitrate from the topsoil (0–30 cm) and shallow subsoil (0–60 cm) ranged from 27 to 41%, and from 7 to 14% of autumn content, respectively. The risk of leaching below 60 cm and 90 cm was near to none during the experimental years due to the exceptionally low precipitation. High nitrate content in subsoil layers below 60 cm constitutes risk of leaching and water pollution due to shallow root systems of many vegetables and potatoes in seasons with normal weather and higher water percolation.

The 13C Discrimination of Crops Identifies Soil Spatial Variability Related to Water Shortage Vulnerability

“…The area is used for the cultivation of irrigated vegetables and early and medium potatoes. Monitoring of crop production and soil mineral N (NO 3 -N + NH 4 -N) content down to a 120-cm depth in the area showed high nitrate contents in the deep subsoil layers (under 60 cm), not accessible to the roots of many vegetables and potatoes [21,22]. This can be linked to the observed trend of increasing nitrate concentrations in extracted water in the last two decades.…”

“…The risk of nitrogen losses is enhanced by worsened growth and yield, leading to lower utilization of N from conventionally applied fertilizers and a higher residual nitrate content [5]. Both experimental regions are known for a higher risk of nitrate loss by leaching [16,21,47,48] and both are included in the nitrate-vulnerable areas that encompass 49% of the agricultural soils in the Czech Republic. The adoption of precision agriculture approaches, including precision irrigation [49], respecting the spatial variability of soil water capacity and the vulnerability to drought, may significantly improve the nitrogen efficiency of crops [50].…”