Effect of applied N concentration in a fertigated vegetable crop on soil solution nitrate and nitrate leaching loss

Pepper was grown, in soil, in two greenhouses using drip irrigation and fertigation. In one greenhouse, the "conventional" treatment, the NO3- concentration in the applied nutrient solution was 10-12 mmol L-1, consistent with local practice. In the other, the "reduced N" treatment, there was a targeted reduction of 20% in the applied NO3- concentration, which resulted in applied NO3- concentrations of 7-9 mmol L-1. In both treatments, the applied NH4+ concentration was 1.5-2 mmol L-1. For 3 weeks, irrigation was given in accordance with local practices, and thereafter using tensiometers (45 to -25 kPa). Drainage was collected with free-drainage lysimeters. Total amounts of N applied were 194 and 168 kg N ha(-1), and of NO3--N leached were 64 and 61 kg N ha(-1); the respective differences were 14 and 7%. Drainage was a major determinant of NO3- leaching; 80% of drainage and N03 leaching occurred in the first 6 weeks, when only 39% of the N had been applied. After 10 weeks when little drainage occurred, the NO3- concentration in the soil solution at 0.13 m depth was very responsive to the different N management treatments. During this period, soil solution NO3- concentration in the conventional treatment increased considerably, and was 80-144% greater than that in the reduced N treatment, which declined slightly over time. These data suggest that when there is little drainage, tendencies in soil solution NO3- concentration may be useful as an indicator of the adequacy of N nutrition.