Environmental implications of low nitrogen use efficiency in excessively fertilized hot pepper (Capsicum frutescens L.) cropping systems

Abstract

Abstract A randomized-block greenhouse plot experiment was conducted on N utilization efficiency and N losses in intensive hot pepper ( Capsicum frutescens L.) production systems typical of commercial practice in Shouguang, an important vegetable production area in Shandong province, northeast China. Crop yield and N utilization, soil mineral N dynamics and potential nitrate leaching losses were studied in control plots receiving no N fertilizer or organic manure and in experimental plots receiving 0, 600, 1200 or 1800 kg urea-N ha −1 plus a basal dressing of 15 t ha −1 air-dried poultry manure supplying 178 kg N ha −1 . Ammonia volatilization from the soil surface was monitored. A microplot was established in each of the plots receiving 1200 kg urea-N ha −1 (the local average commercial fertilizer N application rate), the urea applied to the microplot was labelled with 10 atom % 15 N tracer and residual soil 15 N and 15 N in harvested plant parts were determined. Previous intensive cropping led to a very high residual soil mineral N content (1117 kg N ha −1 ) before the experiment began and control plots gave a satisfactory mean fruit yield of 5.7 t DM ha −1 with no significant yield response to applied fertilizer and poultry manure. Only 10% of applied fertilizer N was recovered in the aboveground parts of the crop and about 52% was lost from the soil–plant system. Substantial nitrate leaching losses occurred using the two highest fertilizer N application rates but there was little NH 3 volatilization from the soil surface. In a survey of 94 wells in Shouguang, the NO 3 − –N concentrations in water used for drinking and irrigation were determined. Almost half of 94 local wells surveyed had NO 3 − –N concentrations above the USEPA public drinking water maximum contaminant level of 10 mg L −1 . The data indicate that N inputs for intensively managed vegetable crops in northeast China should be reduced urgently to maintain crop yields while avoiding serious long-term environmental damage.