Effect of Compost and Mixed Oilseed Cake Application Rates on Soil Chemical Properties, Plant Growth, and Yield of Organic Bulb Onions

Abstract

This study was performed to determine the effect of the application rate of beef cattle manure compost (BCMC) and mixed oilseed cake (MOC) on soil nutrients, plant growth, and bulb yield of intermediate-day onions (Allium cepa L.) in two different locations over two consecutive growing seasons. Trials were conducted at two organic onion growers' fields (one in Sangju county and one in Hamyang county) during the growing seasons of 2012/2013 and 2013/2014. Treatments included BCMC applied at a rate of 0 or 30 t(.)ha(-1) and MOC applied at rates of 0, 3, 6, and 9 t(.)ha(-1). The average air temperature in 2013/2014 was higher than that in 2012/2013 at both sites. All soil nutrient contents in the experimental fields were higher at harvest in 2013/2014 than in 2012/2013 except for exchangeable calcium. Soil nutrients were higher at harvest in Sangju than in Hamyang except for available phosphorus. Soils incorporated with BCMC had higher electrical conductivity, nitrogen, average phosphorus, and exchangeable potassium contents compared with soil without compost. Onions grown in 2013/2014 at Hamyang with BCMC produced higher yields compared to those grown in 2012/2013 at Sangju without BCMC. However, differences in plant growth between the two experimental sites and among MOC application rates were not affected by soil nutrient content. Onions grown in 2013/2014 at Hamyang with BCMC produced higher yields compared to those in grown in 2012/2013 at Sangju without BCMC. Application of MOC increased bulb yield compared with no MOC; however, there was no significant difference among application rates. Therefore, we recommend applying BCMC at a rate of 30 t(.)ha(-1) every year and restricting MOC fertilizer applications to 3t(.)ha(-1) based on soil nutrient status to produce optimum organic onion yields.