Keywords:  drip-fertigation, green pepper growth, lysimeters, mulching materials, nitrate concentrations, nitrogen leaching

Abstract: There is increasing concern about contamination of groundwater by nitrates in regions of intensive agriculture. High-value, intensively managed crops, like vegetables and other irrigated horticultural crops, to which relatively large amounts of N fertilizer are usually applied, have the highest potential for contributing to surface and groundwater contamination. The two-year lysimeter trial was set up in the Vrana basin in the Mediterranean region of Croatia with the aim to determine how the application of different mulching materials and drip-fertigation influence the leaching of nitrate in pepper growing. Green pepper (Capsicum annuum L.) cv. Istra F₁ was grown for 2 years in a trial with three treatments: control without mulch, mulch of black polyethylene PE film and mulch of biodegradable cellulose film (biopack), while an additional treatment with mulch of transparent, photodegradable film was included in the second year. The rainfall in the growing period amounted to 390 mm in 1995 and 496 mm in 1996. The highest nitrate concentration of 73.75 NO₃-N/L was recorded in the percolate from the treatment without mulch. The highest recorded concentration under biopack was 27.29 mg NO₃-N/L and 16.55 mg NO₃-N/L under black PE film. In 1996 the highest nitrate concentration of 25.01mg NO₃^-N/L was determined in percolate under photodegradable film. Total amounts of 20.45 kg N/ha and 18.77 kg N/ha were leached in the treatment without mulching in 1995 and 1996, respectively. 4.45 kg N/ha and 7.41 kg N/ha were leached under black film and biopack, respectively, in 1995, and 9.29 kg N/ha under black film and 12.96 kg N/ha under biopack in the following season. Large differences in quantities of nitrogen leached per trial treatments result also from the differences in plant lushness during the growing period as well as total crop yields. In initial development stages, nitrogen use efficiency is particularly low for green pepper while relatively high nitrogen reserves in the soil are supplied by basal fertililzation. Mulching generally reduces infiltration of rainfall into the soil and thus leaching, resulting in relatively greater proportion of fertilizer to remain in the root zone. This beneficial effect of mulching on nitrogen leaching was particularly expressed in the first trial year owing to higher runoff at the beginning of the growing period.

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