不同耕作模式下稻田水中氮磷动态特征及减排潜力

通过微区模拟稻田试验, 研究了夏季施肥免耕、浅耕和深耕3种耕作模式下不同滞水时间稻田排水中氮磷的动态特征及总氮、总磷流失潜能。结果表明:(1)3个耕作处理5 d后的稻田滞排水中TN、NH⁺₄-N、TP和DP 均处于较低的浓度水平, 免耕的田面水中NO^-₃-N浓度较低。(2)不同耕作模式滞水5 d后TN的绝对流失量均处于较低水平。深耕处理的稻田水中TN的流失潜能相对较小。不同耕作模式处理后氮素的相对流失形态与潜能以TN为主。(3)浅耕处理田面水中TP绝对流失量和相对流失潜能最少。不同耕作模式滞水5 d后排水可显著减少田面水中TP流失。不同耕作模式处理田面水中磷素流失形态随时间呈TP与DP交替变化。因此, 从减少田面水中氮磷的绝对流失量出发, 夏季浅耕不失为最佳清洁耕作模式;同时滞水5 d后排水能有效减少田面水中氮磷的流失量, 减少稻田排水对面源污染的影响。

Dynamic changes in nitrogen and phosphorus concentrations and emission- reduction potentials in paddy field water under different tillage models

Traditional agricultural production in frequently cropped soils can lead to soil structural damage, a decrease in soil quality, increased erosion, and aggravation of nitrogen (N), phosphorus (P) and pesticide losses into rivers and lakes. Aiming at reducing these problems, many countries have introduced the practice of no-till. In southern China, rice farming activities involves deep plowing in spring, but in summer, cultivation involves no-till or shallow plowing. No-till means that the land is not used as intensively and direct sowing or planting crops is the preferred method of production. China from the end of 1970s began to use the no-till approach in paddy field research; in southern China in the 1980s the natural no-till method became popular to improve the environment as a whole and, as well as promoting the sustainable development of paddy field ecosystems. Summer precipitation and paddy field surface water with high N and P concentrations can be the source of the loss of a large quantity of nutrients from runoff from the rice fields, which has the potential to be a source of pollution and can affect the water quality of the local river and lakes. In summer a different farming mode involving changing the paddy field surface water is used, which can reduce N and P losses. The dynamic changes in N and P concentrations and their loss potentials and reduction effectiveness in paddy field surface water, under different stagnating times in three tillage models such as no cultivation, shallow plowing and deep plowing were investigated. This was done using a paddy simulation microzone experiment. Results showed that: (1) Deep plowing was favorable for the fixation of fertilizer, by the soil but total N and NH⁺₄-N in the water showed a gradual decrease with time. The microbial environment in the soil of non-cultivated and shallow plowing scenarios was favorable for nitrification, to which NO^-₃-N was released rapidly into the water as it was poorly adsorbed by the soil. The total P (TP) and dissolved P (DP) concentrations in the water of the non-cultivated and deep plowing systems were relatively high within 1-5 d, and the TP and DP concentration (when the discharge of the water from the three tillage regimes was delayed) was relatively low after 5 days. (2) The absolute TN losses from the water of the different tillage models were low after the water was left for 5 days. Non-cultivation, shallow plowing and deep plowing reduced the TN loses by 59.6%-65.7%, 70.2%-88.2% and 65.2%-77.3%, respectively. Total-N potential losses into the water of the deep plowing regime were relatively minor but were the main form of N lost in the water of all three farming scenarios. (3)The absolute losses of TP in the water of the non-cultivated regime were the highest while they were was lowest in the water of the shallow plowing system. After holding the water for 5 days, the TP lost (as calculated by the three tillage models) was reduced in the range of 54.7%-67.8%, 63.0%-85.1% and 52.5%-88.0%, respectively. The relative potential losses of TP in water of the shallow plowing regime were lower than others. Likewise, the relative form of N and P lost was different in three tillage models and showed variations over time. Thus, when discharged after 5 days' delay, the amount of N and P in the water lost from the paddies can be decreased effectively, which will significantly reduce the effect of paddy water discharge as an agricultural non-point source of pollution.