Sustaining agriculture production and controlling environmental phosphorus (P) pollution have been hot issues of social concern for decades in China. Massive studies focused on mysteries between human activities and environmental factors - the relationship between soil phosphorus status and net anthropogenic phosphorus input (NAPI) was one of them.

Anthropogenic inputs of P fertilizers is a good agent for increasing production, agronomic effectiveness and environmental mobility of soil P is often significantly correlated with the soil available P (SAP) content of the surface soil, which is an indicator of environmental quality and agronomic productivity.

However, few studies have estimated the long-term temporal dynamics of anthropogenic inputs of P at a regional (county) scale or their relationship to changes in SAP content in Chinese subtropical region.

Based on statistical data, through uncertainty analysis and variation partitioning analysis, researchers from China Agricultural University and the Institute of Subtropical Agriculture (ISA) of the Chinese Academy of Sciences estimated the NAPI and determined the SAP content in eight counties in subtropical China from 1980 to 2010.

The researchers found that the NAPI values varied dynamically (318–924 kg P km^-2 yr^-1 in 1980 to 865–3601 kg P km^-2 yr^-1 in 2010) at the county scale in the Chinese subtropical region, in which the P fertilizer application was the largest source, accounting for 36.1–74.6%.

It was substantially larger than those at the national and provincial scale, indicating that there is loss of sensitivity when assessments are averaged over national and provincial scales.

Furthermore, the NAPI in agricultural land (NAPIa) was the largest component of the NAPI, and 60.7–77.1% of the NAPIa accumulated in the upper 20 cm layer of agricultural soils.

"The NAPIa significantly increased soil SAP contents. The increases in SAP, resulting from 10,000 kg P km^-2 of the NAPIa, were estimated to be 1.61–4.36 mg P kg^-1 in the counties. The SAP content in surface soil strongly determined agronomic effectiveness and environmental mobility of soil P, and the soil pH and organic matter content were the most important factors influenced the reactions between SAP and NAPIa," said MENG Cen, one of the researchers.

The mysteries of agricultural P input and environment quality, even some contributing factors, were clear gradually through this study.

The research was supported by the National Key Research and Development Program of China, the Key Programs of the Chinese Academy of Sciences, and the Youth Innovation Team Project of ISA, CAS.

The study entitled "Response of regional agricultural soil phosphorus status to net anthropogenic phosphorus input (NAPI) determined by soil pH value and organic matter content in subtropical China" was published in Chemosphere.