From 1995 to 1999, a field experiment was conducted with calcareous soil of high phosphorus content to determine most
effective methed of the phosphoric fertilizer in a rice-wheat or
wheat-rice cropping system. The results were: 1). With the increase of P fertilizer rates (0, 45, 90, 135 kg·hm -2 ) to rice or wheat, the available P content of the soil increased, and had a marked effect on the increase of the grain yield in present rice season. The residual effects of phosphorus applied to the succeeding crop wheat were significant, and maintained the higher grain yield of succeeding crop, but the available P decreased; 2). Under high yield condition of wheat-rice or rice-wheat period of crop rotation, the phosphorus application of 135 kg·hm -2 for wheat or 90 kg·hm -2 for rice were suitable. P fertilizer applied at one time each year to meet the needs on growth and differentiation of rice or wheat; 3). To come into a conclusion, the practice of supplying phosphorus in rice season could be decreased to 45 kg·hm -2 to maintain the higher grain yield of both rice and wheat. On the other hand, wheat was sown by broadcast sowing with rice growing in the rice cropping zone in North China. For this reason, application of base fertilizer was more difficult. Therefore, the application of
phosphoric fertilizer was suitable for rice season.