Soil Fertility Comparison between Rotations of Tobacco-Rice (TR) and Rape-Rice (RR)

Tobacco-planting plays an important role in ensuring the high-quality tobacco raw materials supply and the local social and economic development in Chenzhou City. In recent years whether tobacco-planting is better for the maintenance and improvement of soil fertility than other crop-planting has been highly concerned. In this study, 16 soil fertility indicators and soil integrated index (IFI) were compared by 21 pairs of fields in Chenzhou city under the rotations of tobacco-rice (TF) and rice-rice (RR), and results showed that, comparing the mean values of soil fertility indicators, the contents of OM, TN, AN, AK, S and IFI were extremely significantly higher in TR than those in RR (p < 0.01), the contents of Cu, Ca, Mg and Fe were significantly higher in TR than those in RR (p < 0.05), but Mn content was significantly lower in TR than those in RR (p < 0.05). Meanwhile the contents of TP, TK and AP were insignificantly higher in TR than those in RR, and the contents of B, Mo and Zn were insignificantly lower in TR than those in RR. The above significant differences in soil fertility indicators were mainly due to relatively higher fertilizer inputs and less nutrient removal during tobacco-growing season than during rape-growing season, the net increase of N, P2O5 and K2O are 8.61, 5.25 and 24.89 kg per 667 m2 respectively in tobacco-growing season, while the net decrease of N, P2O5 and K2O are 8.88, 4.70 and 4.62 kg per 667 m2 respectively in rape-growing season. C.V. of soil fertility indicators and IFI were meanly lower in TR (52.25% and 15.95%, respectively) than those in RR (63.07% and 22.12%, respectively). Comparatively, tobacco-planting can improve soil fertility better than rape-planting when rotated with late rice in Chenzhou city. For tobacco-planting, Mg fertilizer should be applied for 23.8% TR fields, while more N, K, Ca, Mg, S and B fertilizers should be applied for 42.86%, 23.81%, 14.29%, 47.62%, 80.95% and 47.62% RR fields, respectively.

Effects of Long-term K Fertilizer Application on the Crop Yield and K Distribution of Soil Aggregates in a Paddy-Upland Rotation System

[Objective]A long-term paddy-upland experiment was conducted to evaluate the effects of the recommended amount of potassium( K)fertilizer on crop yield,distribution of soil aggregate,and soil available K content. It was mainly to ascertain the distribution of K in the soil aggregate components in the paddy-upland rotation system,and then to provide theoretical basis for soil structure improvement,K pool management,and reasonable application of K fertilizer. [Method]There were 2 treatments selected,namely,NP(-K) treatment and NPK( + K) treatment in this study. Then the effects of K fertilizer application on the yield,available K content,and aggregate distribution in the middle rice-winter rape rotation system were analyzed. [Result]The results showed that the output of the crop rotation was affected by the year and fertilization. Compared with NP(-K),the average yield increases of rice and winter rape after application of K fertilizer were 0.51 and 0.33 t/hm2,with the increments of 7.5%and 14. 1% respectively. The long-term application of K fertilizer( 7 a) had no significant effects on the distribution of soil aggregates but could significantly increase the water-soluble K content and available K content at depths of 20-30 and 30-40 cm,and available K content of aggregates in each particle size. In addition,the balance of available K at the 10-20 and 30-40 cm of soil layers was the most significant through calculation of surplus-deficit value of available K in agglomerates of different soil layers. [Conclusion]Compared with the initial available K content in the farmland in 2011,the current K fertilizer application could lead to that farmland K content continues to decline. Therefore,we should pay attention to straw returned and supplement of organic K fertilizer,to maintain crop rotation system's productivity and soil K balance.

不同轮作模式下氮肥用量对土壤有机氮组分的影响

通过三年六季的田间定位试验,对比研究了水旱轮作(水稻/油菜)和旱地轮作(棉花/油菜)下氮肥用量对土壤有机氮含量及其组分的影响。结果表明,经过三年轮作后,周年轮作氮肥投入超过300 kg hm^(-2)(以纯氮计,下同)的处理0~20 cm土壤全氮含量明显增加。与不施氮处理相比,周年氮肥用量为300 kg hm^(-2)和375 kg hm^(-2)水旱轮作处理0~20 cm土壤全氮含量增加了13.6%~23.5%,而旱地轮作处理则增加了15.0%~23.0%,土壤酸解态氮含量增加是土壤全氮变化的主要原因。两种轮作模式下土壤酸解态氮含量无显著差异,但土壤酸解态氮各组分的变化却不相同。水旱轮作中酸解铵态氮增加的比例(33.8%)低于旱地轮作(53.9%),但其酸解未知态氮含量增加的比例(36.0%)高于旱地轮作(16.6%)。综上所述,周年氮肥合理施用能明显提高土壤有机氮含量,水旱和旱地轮作下土壤酸解态氮库各组分变化差异明显。根据不同轮作模式下土壤有机氮库转化特点,优化氮肥施用对于提高作物产量和氮肥利用率具有重要意义。