Nitrate Availability in No-till Agricultural Systems and their Relationship with Environmental and Management Variables

Abstract

Nitrogen (N) is the nutrient that most frequently limits crop production. In deciding nitrogen fertilization on wheat and barley in Uruguay two models are used, one developed by the School of Agriculture (Universidad de la República) and other developed for the Rolling Pampa in Argentina. Both take into account nitrate concentration at sowing. The objectives of this research were:
i) generating an empirical model to estimate N-NO₃- concentration in the first 20 cm depth, ii) establishing the N contribution in the current production systems, and iii) to relate the N-NO₃- concentration in the first 20 cm depth with the concentration in the 20-40 cm layer. 274 management units were collected from CREA farmers that determined the N-NO₃- concentration before sowing (0-20 y 20-40 cm) between 2009 and 2012, and had records of precipitation and management practices. The timing of soil samples distribution were similar between years (80% between May and June). The N-NO₃- concentration was significantly higher in 2009 (12 mg.kg^-1), followed by the year 2012 (9 mg.kg^-1), while 2010 and 2011 years had a lower concentration and not different from each other (8 mg.kg^-1). Rainfall occurred within the 50 days prior to the sampling determi-ned N-NO₃- concentration (0-20 cm). Either the excess (≥216 mm) as the deficit (<2mm) in precipitations decreased the concentrations. The relationship between N-NO₃- in surface and depth was significant (R² = 0.60; P<0.0001). However, the variability would not allow to predict N-NO₃- in depth with precision.