Straw and optimized nitrogen fertilizer decreases phosphorus leaching risks in a long-term greenhouse soil

Purpose

Phosphorus (P) mobility in soil is controlled by its forms and soil sorption capacity. The P forms and soil sorption capacity are both affected by nitrogen (N) and carbon (C) addition. This paper aimed to (i) analyze effects of N and straw application on the different forms and content of P in the soil and its leachates in greenhouse soil, and (ii) explain variations in soil P transformation and transport in terms of contributing soil factors.

Material and methods

In this study, the impacts of N and straw application on the transformation and transport of soil P were investigated after 17 years in a greenhouse. Four fertilization regimes were implemented: farmer standard fertilization practice (CK), straw incorporation treatment (SC), optimized N fertilizer application (ON), and combined straw and optimized N fertilizer application (SN). P forms and its contents were determined in the selected leached water and its related soil samples.

Results and discussion

Compared with CK, ON treatment significantly (p < 0.05) decreased total phosphorus (P_t) and the proportion of organic phosphorus (P_o) in soil, while straw amendment did not affect soil P_t content. SC, ON, and SN all decreased soil available phosphorus (P_a) but enhanced P transformation, as evidenced by the increase in the ratio of P_a to P_t and microbial phosphorus (MBP) and alkaline phosphatases (ALP) in soil. After SN implementation, soil P adsorption capacity increased significantly and was associated with higher soil organic matter (SOM) and CaCO₃. ON showed lower P_t in the leachate than CK, but SC did not lead to significantly different. Under the SN regime, P_t loss by leaching decreased by 29.4% compared with CK and significantly reduced proportion of total dissolve P (DP_t) in leachate.

Conclusions

Our study highlights that straw and optimized N fertilizer in SN treatment not only generates lower P loss by leaching but also promotes the transformation of soil P, which were attributed to higher soil P_a in greenhouse soil. This finding further indicates that P transformation and transport in the different fertilizer regimes was primarily linked to pH and SOM in greenhouse soil.