Yield, fruit quality of pepper and nitrogen loss under different amide/nitrate ratios in three types of soils

ObjectivesThe main nitrogen sources of vegetable fertilization are amide nitrogen, ammonium nitrogen and nitrate nitrogen, and nitrogen transformation process differs from soil to soil. In order to determine the appropriate nitrogen forms and ratios of main soil types in the major pepper producing areas, the red soil (pH 5.97), vegetable soil (pH 7.09) and fluvo-aquic soil (pH 8.33) from Guangdong, Anhui and Shandong were selected to study the response of pepper yield and quality under different forms and ratios of nitrogen, to determine the appropriate CO(NH₂)₂-N/NO₃-N in different soil types, and furthermore, to provide the theoretical basis for the control of nitrogen fertilizer in the main pepper production areas.

MethodsSoil culture experiment and pot experiment were conducted. In the soil culture experiment, there were two treatments in each soil type: control (single urea) and the urea and nitrification inhibitor addition treatment. Six treatments were designed in the pot experiment: no nitrogen application (CK), NO₃-N 100% (T1), CO(NH₂)₂-N 25% + NO₃-N 75% (T2), CO(NH₂)₂-N 50% + NO₃-N 50% (T3), CO(NH₂)₂-N 75% + NO₃-N 25% (T4) and CO(NH₂)₂-N 100% (T5). In the soil culture experiment, the soil ammonium and nitrate nitrogen contents were determined during different culture periods. In the pot experiment, the yield, quality and plant nitrogen content of pepper were determined after the harvest, and the soil inorganic nitrogen was determined after the fertilization.

ResultsThe results obtained from the soil culture experiment indicated that the nitrification ability of the three soil types were in order: fluvo-aquic soil > vegetable soil > red soil. Adding nitrification inhibitors N-Serve can slow down the process of nitrogen transformation in three kinds of soils, and the apparent nitrification rates were decreased by 30.3%, 38.0% and 8.3% respectively after four incubation days. The pot experiment showed that compared with the CK treatment, applying nitrogen can improve the yield and quality of pepper significantly, furthermore, the increase in yield was duing to the increase in fruit weight and fruit number, and the improvement in quality was duing to the increases in vitamin C and soluble solids content. Under the condition of adding N-Serve (1% of pure amide nitrogen) in soil, the response of yield and quality of pepper to the CO(NH₂)₂-N/NO₃-N was different in different soils. The highest yield was obtained with a proportion of nitrate nitrogen at 75%, 25% and 50% in fluvo-aquic soil, vegetable soil and red soil respectively, and the proportion for quality was 75%, 50% and 25% respectively. The nitrogen uptakes also showed vegetable soil > fluvo-aquic soil > red soil. Compared with the only applying nitrate treatment, applying nitrate nitrogen and amide nitrogen with a proper ratio can improve the nitrogen use efficiencies by 22.4%, 9.0% and 25.3% in fluvo-aquic soil, vegetable soil and red soil respectively, and reduce nitrogen losses by 51.7%, 53.6% and 58.4% respectively.

ConclusionsConsidering the factors of high yield and high quality of pepper and the environmental cost together, the appropriate proportions of nitrate nitrogen in red soil, vegetable soil and fluvo-aquic soil were 50%–75%, 25%–50% and 25%–50% respectively.