Excessive Fertilization is Detrimental to Yield and Quality for Onion Grown on High Organic Matter Content Paddy Soils

Abstract

Excess chemical fertilizer applications in historical onion (Allium cepa L.) cultivation areas in Korea may be detrimental to onion yield and quality. A field study was performed to evaluate the effects of chemical fertilizer rates and split applications on intermediate-day onion growth, yield, storage quality, and soil chemical properties in plants established in a paddy soil with high organic matter (OM) content. Rates of chemical fertilization, based on a soil test recommendation (192–13–213 kg·ha⁻¹ N–P–K), and twice the recommended rate were applied and compared to a control treatment not receiving fertilizer. Treatments with twice the recommended rate were applied in three, four, or five splits. Preplant soil contained 46.3 g·kg⁻¹ OM, 728 mg·kg⁻¹ available phosphorus, and 17.3 mg·kg⁻¹ nitrate nitrogen. The highest marketable yield, 58.1 Mt·ha⁻¹, was achieved at the recommended rate, 7.3%–20.0% more than the double rates and the control. Increased fertilizer beyond the recommended rates and delayed split application times had no positive effect on onion growth or yield but increased culls and accumulated soil electric conductivity, OM, exchangeable K, and NO₃-N content in soil at harvest. Soil NO₃-N contents ranged from 110 to 316 mg·kg⁻¹ for split applications at the double rates. The control yielded 40.8 Mt·ha⁻¹, which was 70.2% of the highest yield. Storage quality was not affected due to treatment, although there were slight increases in bulb rot and physiological disorders at the double rate. Fertilizer applied at higher than the recommended rate for onion is not beneficial.

Keywords:

• Allium cepa L
• Chemical fertilizer
• Intermediate-day onion
• Soil properties
• Storage quality

Acknowledgments

The authors thank Professor Clinton C. Shock at Oregon State University for constructive comments and suggestions to improve this manuscript. This research was financed by Locally Specialized Agricultural Techniques from the Korean Rural Development Administration, Republic of Korea.