不同耕作制度和地下水位对水田土壤有机质及氧化铁含量的影响

连续四年在水泥模拟池内进行了不同耕作制度、不同地下水位和不同施肥制度,对土壤有机质和氧化铁含量影响的研究。结果表明:不论何种处理,水田土壤有机质均有所增加,不同耕作制度,以冬泡区土壤的有机质增加最多,但只施化肥进行冬泡的有机质量增加极少,并且第四年开始降低。施用常量有机肥的土壤有机质含量是:高水位区>低水位区;而不同地下水位对施用高量有机肥的土壤有机质含量影响不大。各处理土壤中的无定形氧化铁含量及其活化度均逐年有所增加。无定形氧化铁的含量一般是:耕层>下层,冬泡区>冬作区,高量区>常量区>化肥区。耕层无定形氧化铁含量主要决定于水分和有机质含量,下层则主要受地下水位高低的影响。无定形氧化铁含量与有机质含量之间有一定的相关性。活化度及其变化规律与无定形氧化铁的状况相似。

EFFECTS OF CROPPING SYSTEMS AND GROUND-WATER LEVELS ON THE ORGANIC MATTER AND IRON OXIDES IN FLOODING PADDY SOIL

Plot experiments in the paddy soil developed from quaternary red earth have been conducted in cement model plots for four years. Effects on the status of soil organic matter and iron oxides were estimated with cropping systems (early rice-late rice-green manure crop, early rice-late rice-rape, and early rice-late rice-winter flooding), different amount of green manure applications (none, normal and heavy applications)and different ground-water levels (20cm and 80cm). Organic matter was increased in all treatments, among which, at any conditions, the early rice-late rice-winter flooding treatment increased most, none of green manuring increased least and began to decrease in the fourth year. For normal manuring, organic matter content of high ground-water level treatment is higher than that of low ground-water level treatment; whereas the difference in organic matter between ground-water level treatments is insignificant in heavy manuring, Amorphous iron oxide and activation percentage of iron oxides in all treatments increased gradually and steadily. Amorphous iron oxides of plough horizons for all the treatments were higher than that of their subhorizons. Amorphous iron oxide amounts of various treatments were as follows: winter flooding>winter cropping; heavy green manuring>normal green manuring>none green manure. The amorphous iron oxide contents of plough horizons depended mainly on soil moisture regime and organic matter; whereas the amorphous iron oxide content of subhorizons were in flueneed by ground water level. Amorphous iron oxide contents and the iron oxide activation percentage correlated with soil organic matter to a certain extent.