摘 要：
【Objective】The Loess Plateau in Central Gansu is one of the most seriously eroded regions in China. In this area the soil is generally in lack of phosphorus, and the conventional tillage pattern prevailing in the region exacerbates the loss of phosphorus and other soil nutrients. Therefore, it is urgent to address the problem by improving farmland management and hence to uplift utilization efficiency of soil phosphorus. This study attempts to characterize dynamic changes of soil total phosphorus and phosphorus fractions in the soil under six different tillage patterns, so as to reveal mechanisms of the six tillage patterns affecting soil phosphorus, and provide a theoretical basis for remolding the original tillage pattern or establishing a new sustainable tillage pattern.【Method】For this study, a 13-year-long field experiment on tillage has been carried out in an upland farm on the Loess Plateau in Central Gansu. The experiment is designed to have six different tillage patterns, that is, conventional tillage(T), no-tillage( NT),conventional tillage with straw incorporation( TS), no-tillage with straw mulching( NTS), conventional tillage with plastic mulching(TP), and no-tillage with plastic mulching( NTP). For in-lab analysis,Tiessen's modified Hedley method was used for fractionation of soil phosphorus. Six extractants were used sequentially from weak to strong in capacity to extract nine fractions of phosphorus, that is,Resin-Pi,NaHCO_3-Pi, NaHCO_3-Po, NaOH-Pi, NaOH-Po, D.HCl-Pi, C.HCl-Pi, C.HCl-Po and Residual-P.【Result】Results show:(1) During the experiment, soil total phosphorus in all the treatments increased year by year, with a rate ranging from 8.1% to 15.6%, and in terms of soil phosphorus increase rate, the six treatments exhibited an order of NTS>TS>NTP≈NT≈T≈TP. Total inorganic phosphorus also showed an increasing trend in all the treatments. In Treatments NTS and TS, total organic phosphorus increased the fastest or by48.7% and 46.0%, respectively, and in Treatments NTP and NT it did by 18.9% and 16.3%,respectively, while in Treatments T and TP it remained almost unchanged;( 2) During the experiment,all the fractions of inorganic phosphorus were on a rising trend, except for Resin-Pi and NaHC03-Pi, which declined slightly in 2011. Among all the inorganic phosphorus fractions, NaOH-Pi rose the fastest with an average growth rate of all the six treatments reaching up to 253.6%; Resin-Pi and NaHCO_3-Pi followed, with an average growth rate being 128.6% and 66.9%, respectively; And the relative content of the three fractions also some what increased;( 3) NaHCO_3-Po and NaOH-Po showed an overall increasing trend except for a slight fall in 2011 in the five treatments of conservation tillage, however, they did not change much in Treatment T, throughout the entire experiment. C.HCl-Po increased year by year in Treatments TS and NTS,and remained almost unchanged in Treatment T, and showed overall downward trends in Treatments NT,TP and NTP;( 4) The five patterns of conservation tillage raised the content of Resin-Pi、NaHCO_3-Pi and NaOH-Pi, and no tillage was more effective than conventional tillage, when the same in supplementary measure, with Treatment NTS in particular, which increased the content of D.HCl-Pi. The effect of tillage on C.HCl-Pi and Residual-P was not obvious. The five treatments of conservation tillage, especially Treatments NTS and TS, increased the content of NaHCO_3-Po and NaOH-Po, and Treatments NTS and TS, also raised the content of C.HCl-Po, but Treatments NT, TP and NTP reduced the content of C.HCl-Po, in comparison with Treatment T.[Conclusion]Phosphorus fertilizer would accumulate in the soil year by year, existing in the soil in the form of NaOH-Pi, moderate in activity and in the form of Resin-Pi and NaHCO_3-Pi, high in activity, and the accumulation does not have much impact on fractions of organic phosphorus. Sparse rainfall is no good to accumulation of phosphorus of active fractions, such as Resin-Pi, NaHCO_3-Pi and NaHCO_3-Po, but conducive to that of phosphorus of stable fractions, such as D.HCl-Pi and C.HCl-Pi. Conservation tillages may increase the content of phosphorus of the fractions, moderate and high in activity, especially Treatment NTS. Therefore, it can be concluded that the adoption of conservation tillage can reduce the consumption of phosphorus fertilizer to a certain extent. Conservation tillage, especially the practice of notillage with straw mulching, is worth promoting in this area.
