From 1990,over 17 years field experiment was carried out in paddy field cultivated from infertile upland to evaluate the response of rice productivity,soil organic carbon(SOC),and total N to long-term NPK fertilization or NPK combined with organic amendments.The field trials included NPK(N,P,K fertilizer),NPKRS(NPK combined with rice straw),NPK2RS(NPK combined with double amount of rice straw),NPKPM(NPK combined with pig manure) and NPKGM(NPK combined with green manure) and the cropping system was rice-rice(Oryza sativa L.) rotation.Annual rice yield,straw biomass,and harvesting index increased steadily with cultivation time in all treatments.Average annual rice yield from 1991 to 2006 was ranged from 7 795 to 8 572 kg ha-1 among treatments.Rice yields in treatments with organic amendments were usually higher than that in treatment with NPK.Contents of SOC and total N also increased gradually in the cultivation years and reached the level of 7.82 to 9.45 and 0.85 to 1.03 g kg-1,respectively,in 2006.Soil fertilities in treatments with chemical fertilization combined with organic amendments were relatively appropriate than those in treatment with NPK.There was obvious discrepancy between cumulative characters of rice yield and soil organic fertility in newly formed paddy field.Compared with relatively high rate of crop productivity improvement,cumulative rates of SOC and total N were much lower in our study.SOC and total N contents were still less than half of those in local highly productive paddy soils after 17 years cultivation in subtropical China.Present work helps to better understand the development of infertile paddy soils and to estimate the potential of yield improvement in this region.
LIU MingLI Zhong-peiZHANG Tao-linJIANG Chun-yuCHE Yu-ping
