Evaluating organic and conventional management and nitrogen rate for effects on yield, soil and plant nutrient of tomato and pac choi grown under high tunnel and in the field

Abstract

The goal of this study is to clarify the influence of organic fertilizer sources on vegetable crop yield under different production systems. This research hypothesized that organic soil amendments will produce healthy and vigorous plants with similar or higher yields while improving soil organic matter levels compared to conventional amendments. Applying organic fertilizer sources can be cost-prohibitive; moreover, synchronizing timing of crop nitrogen demand with soil plant available nitrogen is essential to maximizing yield and reducing nitrogen pollution to the environment. The objectives of this study are to evaluate yield in relation to soil fertility status at different fertility rates for organic and conventional management in field and high tunnel production systems, to measure plant nutrient status in crop petioles and compare it to available mineral N levels in soil at different growing stages, and to determine the effect of nitrogen availability of organic compared to conventional fertilization on plant available nitrogen and crop yield under both systems. A latin square experimental design was conducted from 2008 to 2010 at Kansas State University Research Center in Olathe KS to evaluate an organically managed vegetable rotation of tomato (Solanum lycopersicum L. ‘Bush Celebrity’) and pac choi (Brassica rapa L. ‘Mei Qing’) under three fertility rates; control, low (composted poultry manure), and high (composted poultry manure and fish hydrolyzate) in contrast with conventionally managed soils under two production systems (field and high tunnel). The effect of these four contrasting systems was measured on plant and soil nutrient status. All plots had cover crops of rye during the winter and buckwheat in the summer between pac choi crops. Soil nitrate-N (NO₃-N) and ammonium-N (NH₄-N) were measured, as well as petiole sap nitrate (NO₃⁻). In tomato, additional soluble fertilizers had no direct effect on yield in both field and high tunnel. Compost application had a positive effect on organic matter. In pac choi, additional liquid fertilizer helped organic field plots obtain maximum yield. Soil mineral nitrogen were affected by production system and fertility source, but statistical significance varied by crop and stage. Petiole sap reflected treatment regimens but not necessarily soil N status at each plant stage. The study also addressed long term management practices on organic and conventional available nitrogen. An incubation study on the soil at the conclusion of the field experiment explored the relationship between N mineralization from potentially mineralizable nitrogen (PMN) compared to Illinois Soil Nitrogen Test (ISNT) in control and pre-plant application fertility treatment for both field and high tunnel systems. The results indicated that ISNT concentration values for all soils were below the proposed value for corn crop suggested by (Khan, 2001). ISNT correlated with PMN with the stronger correlation being in field plots. ISNT also correlated with OM in field. Fertility rate showed a significant effect on total carbon and total nitrogen in organic systems of both field and high tunnel plots. This study supports composted poultry manure to improve the fertility status of the soil and to obtain a yield equal to that of conventionally managed soil.