The long-term effectiveness of biochar in increasing phosphorus availability and reducing its release risk to the environment in water-saving irrigated paddy fields

Improper management practices lead to the reduction of phosphorus availability by rice and an increase in the risk of phosphorus release to the environment in paddy fields. This study aims at exploring the effects of biochar with the applicated rate of 0, 20, 40 t ha- 1 under controlled or flooding irrigation on utilization efficiency of phosphorus fertilizer and phosphorus leaching loss from fields by observing the dynamics of phosphorus in paddy fields throughout the rice growing period. The results indicated that biochar application lessened the TP and DRP leaching loss by 6.77-17.62% and 6.22-10.28% respectively. It was also found that biochar improved the phosphorus efficiency of rice by 5.33-10.33%and reduced the soil phosphorus surplus by 3.45-6.66% for the increased soil Olsen-P concentration and soil solution dissolved reactive P concentration. In comparison with flooding irrigation, controlled irrigation apparently decreased P leaching loss by 34.64-55.15% by controlling the downward migration of phosphorus in soil solution. Although biochar addition in the field increased pro-duction cost, it was proved increasing net economic benefit by 2558-4655 yuan ha- 1 y-1, which attributes to the increased rice yield in biochar applicated treatment. In order to improve phosphorus efficiency of rice and reduce the risk of phosphorus release to the environment, a combination of biochar and water-saving irrigation applied in rice fields can provide cleaner production of rice with a promising option, thus bringing both environmental and economic benefits.