Effects of long-term fertilization on crop yield and indigenous soil nutrient supply in Hexi Oasis of Gansu Province

A long-term(1982-2006)field experiment was conducted on calcareous soils at Zhangye city, Gansu Province under the wheat(Triticum aestivum L.)-wheat-corn(Zea mays L.)rotation system in order to determine the effects of long-term fertilization on crop yields and indigenous P and K supply of calcareous soils. The results show that the average grain yields of the 25 years are decreased in the order of MNPK＞MNP＞NPK＞MN＞NP＞M＞N＞CK. The crop yields are significantly increased under the application of N fertilizer combined with P fertilizer, especially N and P fertilizers combined with the farmyard manure. For the application of K fertilizer, there seem no obvious effects on increase of the grain yields during the initial 6 years(1982-1987), moderate effects in the next 5 years(1988-1992), and significant effects in the last 14 years(1993-2006). Indigenous soil P supply is always decreased from 1982 to 2006, and at present time it is not reach to a stable level, while indigenous soil K supply is relatively steady.