The Effects of Struvite on Biomass and Soil Phosphorus Availability and Uptake in Chinese Cabbage, Cowpea, and Maize

Struvite (MgNH4PO4·6H2O), a mineral with low water solubility that can be recovered from industrial wastewater, has the potential to be used as a slow-release phosphorus (P) fertilizer. However, the effect of struvite on the yield and P uptake efficiency of different crops remains unclear. In this study, the effects of struvite, diammonium phosphate (DAP), and a mixed fertilizer consisting of struvite + DAP (MIX) on biomass, P uptake, and soil P fractions of Chinese cabbage, cowpea, and maize were investigated in pot experiments. The results showed that compared to DAP, the mixed fertilizer reduced the biomass of Chinese cabbage by 47%, while there was no difference in the biomass of cowpea and maize under P fertilizer application. There was no difference in total P concentration in Chinese cabbage and cowpea plants between DAP and MIX, while total P concentration in maize under mixed fertilizer treatment decreased by 16.73% compared to DAP treatment. Compared to DAP, the MIX treatment reduced total P uptake in Chinese cabbage and maize by 45.82% and 33.41%, respectively, with no direct difference in cowpea. Soil Olsen-P and CaCl2-P concentrations were highest in DAP among the different treatments. The MIX treatment significantly increased the water-soluble P in Chinese cabbage and cowpea by 5.87% and 5.23%, respectively, while the water-soluble P in maize was lower in the mixed fertilizer treatment than in the DAP treatment. In addition, mixed fertilizer significantly increased soil pH and soil phosphatase activity compared to DAP. This result suggested that among the three treatments of struvite, DAP, and MIX, struvite had the weakest effect on crop growth. In addition, among the three crops, Chinese cabbage, cowpea, and maize, the compatibility between struvite and maize was the highest. These results provide valuable insights for the future application of struvite in agricultural production for achieving stable yields while mitigating environmental risks.