Change of phosphorus recovery efficiency under long-term fertilization in typical farmland in southern China

Objectives Long-term fertilization changes the phosphorus recovery efficiency (PRE), uptake and cumulative recovery efficiency of phosphorus fertilizer (CPRE). The change characteristics at regional scale were studied in southern China, aiming to provide academic support for the management of phosphorous nutrients.

Methods The selected soils for long-term experiments were the purple soil in Beibei, Chongqing (since 1991), reddish paddy soil in Wangcheng, Hunan (since 1981) and Jinxian, Jiangxi (since 1981). The investigated treatments included no fertilizer application (CK), only rice straw or barnyard manure (M), inorganic nitrogen and potassium fertilizer (NK), NK with pig manure (NKM), inorganic nitrogen and phosphorus fertilizer (NP), inorganic nitrogen, phosphorus, potash (NPK), NPK with pig manure or barnyard manure (NPKM), and NPK with rice straw (NPKS). The phosphorus uptake, PRE and CPRE were evaluated.

Results After 21−27 years’ cultivation without inorganic phosphorus fertilizer input, soil phosphorus supply decreased significantly (P < 0.05) compared with fertilization treatments. The annual decline rates were 0.60, 0.48 and 0.63 kg/hm² for purple soil in Beibei, reddish paddy soil in Wangcheng and Jinxian, respectively. The order of annual average phosphorus uptake under different treatments was as follows: NPK, NPKS, NPKM > NP, NKM > CK, NK (P<0.05). Higher phosphorus uptake was obtained in NPK combined with pig manure than combined with barnyard manure or straw. PRE increased with the increase of fertilization years in all the three experimental sites. The annual increase in PRE was 0.15%−0.94% in NPK, and 0.07%−1.60% in NPKM and NPKS. The CPRE was 37.8%−61.5% in NPK. As compared with NPK treatment, CPRE decreased by 3.0% and 34.3% respectively in NPKM and NPKS.

Conclusions No P fertilization significantly decreased supply of phosphorus to crops, while long-term P fertilization increased P uptake. Crops will absorb significantly more phosphorus under balance NPK fertilization than under unbalanced fertilization. Every increase of 100 kg/hm² in N fertilizer input will increase 5 kg/hm²of P absorption. The P recovery efficiencies increase with the increase of fertilization years. Compared with NPK application, the combined application of NPK with organic fertilizer decrease the cumulative utilization rate of phosphorus fertilizer. Every increase of P fertilizer by 10 kg/hm² will decrease the PRE by 0.9%. Therefore, properly increasing N and decreasing P fertilizer inputs are recommended to improve the utilization efficiency of phosphorus fertilizer when NPK is applied with manure.