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Temporal changes in the concentrations of plant-available phosphorus (P) in soil (Olsen-P), total soil-P and P activation coefficient (the ratio of Olsen-P to residual-P (i.e. an approximation to total-P)) were measured in plots that received consistent inorganic nitrogen, phosphorus and potassium plus organic fertilizers annually. Maize and winter wheat crops were grown in rotation for 24 years. Olsen-P and P activation coefficient declined significantly in the earlier years (< 12 years) for treatments that did not include any P fertilizer, and increased over the same period for the P-fertilized treatments. The rates of change in the Olsen-P and P activation coefficient values were positively related to P balance. In the later years, the Olsen-P and P activation coefficient plateau values were positively related to the P balance. [ABSTRACT FROM AUTHOR]

To understand the mechanisms affecting water balance partitioning during fallow on drylands could improve the fallow management practices in arable land ecosystems. A three-year field experiment was conducted to evaluate the effects of field management regimes on water balance partitioning and fallow efficiency during the fallow periods under a winter wheat (Triticum aestivum L.) fallow system on the Loess Plateau, China. The fallow management regimes tested were: (i) conventional practice, (ii) catch cropping, and (iii) no tillage with wheat straw mulching. A process-oriented ecosystem model (CoupModel) was calibrated with field measurements and then used to generate comparative simulations of the water balance partitioning. The simulations indicated that mulching increased the soil water storage change by 38-71 mm during the three fallow periods, thus resulting in higher fallow efficiency by 9-12%, and decreased soil evaporation by 22-72 mm, compared with the conventional practice. Furthermore, water reached deeper horizons, resulting in 7 mm deep percolation in a wet year under mulching but not under conventional practice or catch cropping. The simulation results also showed that the catch cropping decreased the soil water storage change by 13-21 mm, although it lowered soil evaporation by 11-51 mm, and altogether reduced the fallow efficiency by 3-9%, compared to conventional practice. On the Loess Plateau of China mulching proved to be a sound measure for ensuring certain fallow efficiency and possibly benefit to the water cycle, while catch cropping negatively partitioned the water balance. The catch cropping under mulching might be another management regime to be considered. [ABSTRACT FROM AUTHOR]