Influences of Phosphogypsum Application on Soil Property and Yield and Quality of Onion (Allium cepa L.)

Abstract

Phosphogypsum (PG) is a by-product obtained in the process of manufacturing phosphoric acid (H3PO4). In general, PG is characterized mainly by gypsum, phosphate, sulphate, fluoride etc. Considering the nutritional composition, PG has been globally used as soil fertilizer or amendment in agriculture for decades. This study aimed to investigate effects of PG application on soil properties and yield and quality of onion (Allium cepa L.) and to seek proper rate of PG application in a field. We applied PG into a field with four different levels: 0% (control), 50% (PG50, 104 kg 10a-1), 100% (PG100, 208 kg 10a-1), and 150% (PG150, 312 kg 10a-1). Also, oyster shell (OS) included as a comparable and chemical fertilizer (N-P-K = 8.4-37.9-8.0 kg 10a-1) was supplied into soil of all treatments. Following onion cultivation for 7 months, there was a significant change in soil pH. Indeed, PG application was more likely to lower pH relative to control. With increase in PG application rate, soil EC increased and the maximum value (1.93 dS m-1) was found in soil of PG150. In PG100 and PG150, concentration of exchangeable Ca (Ex. Ca) increased by 5% and 10%, respectively, whilst other treatments representing reduction in the Ex. Ca concentration. In addition, PG application affected concentration of water soluble Ca across the soil profile (up to 70 cm depth) and, in particular, the higher the PG application rate the higher the concentration of water soluble Ca. Similarly, water soluble S had same trend with water soluble Ca in the present study. With increase of PG application rate, yield of onion increased but decreased in PG150 which is the highest rate of PG application. Also, the plant’s uptake for N, P, Ca, K, and S affecting yield, resistance to pathogen and pest, and quality of the crop increased in PG50 and PG100. Moreover, concentrations of total amino acids, cysteine and methionine in onion bulbs that are strongly associated to S uptake increased by PG applications. The increased concentrations of amino acids with PG applications might improve yield, quality, and favor of onions. These results suggest that PG supply could have a potential to enhance soil fertility, contributing to improvement of yield and quality of onions. Further studies are needed to maximize efficiency of PG supply in agricultural lands. Vertical movement of Ca and SO4 across the soil profile following phosphogypsum application.