前氮后移对水稻产量形成和田面水氮素动态变化的影响

通过田间小区试验,在施氮量180 kg/hm~2水平下,设置4个氮肥运筹比例,基肥∶分蘖肥∶穗肥的比例分别为10∶0∶0(T1),4∶3∶3(T2),2∶3∶5(T3),0∶3∶7(T4),研究氮肥后移对水稻产量形成和稻田田面水氮素动态变化的影响。结果表明:与氮肥全部作为基肥施用的处理相比,将前期氮肥的30%甚至50%后移到穗肥施用,对水稻产量没有明显影响,而氮肥后移70%至穗肥会使水稻产量显著下降。田面水中总氮(TN)和可溶性总氮(DTN)浓度在每次施肥后1天达到峰值,铵态氮(NH_4~+-N)浓度在基肥和分蘖肥后1天达到峰值,穗肥后3天达到峰值,随后逐渐降低至与不施氮肥处理相当。整个基肥期、分蘖肥后20天内和穗肥后9天内是防止稻田氮素流失的关键期。施尿素后,DTN是田面水氮素的主要部分,DTN以无机氮(IN)为主,而NH_4~+-N在IN中所占比例达64.0%以上。比较水稻生育过程中氮素流失风险期内的TN、DTN和NH_4~+-N三氮浓度,相比T1,T2的三氮浓度分别降低了2.9%,1.6%,3.1%,T3的三氮浓度分别降低了15.5%,14.7%,22.3%,T4的三氮浓度分别降低了16.1%,22.9%,34.1%,结合产量,确定基肥∶分蘖肥∶穗肥比例为2∶3∶5的氮肥后移措施能够在保证水稻产量不下降的同时,有效降低稻田氮素的流失风险。

Effect of Postponing Nitrogen Application on Rice Yield Formation and Nitrogen Dynamics in Surface Water of Paddy Field

With the nitrogen application rate of 180 kg/hm², four nitrogen application ratios were designed in a field experiment, including base fertilizer:tillering fertilizer:panicle fertilizer=10:0:0 (T1), 4:3:3 (T2), 2:3:5 (T3), 0:3:7 (T4) respectively, to study the effect of postponing nitrogen application on rice yield formation and nitrogen dynamics in surface water of paddy field. The result showed that compared to T1, The treatments with 30% or even 50% of basal nitrogen fertilizer postponing to panicle fertilizer had no significant effect on rice grain yield, while the treatment with 70% of basal nitrogen fertilizer postponing to panicle fertilizer caused a significant decrease in rice grain yield. The peak concentrations of total nitrogen (TN) and total soluble nitrogen (DTN) in the surface water occurred after urea application for 1 day, NH₄⁺-N reached the peak on 1 day after basal fertilizer and tillering fertilizer and 3 days after panicle fertilizer, and then these 3 forms of nitrogen gradually reduced to basically close to the treatment with no urea application. These days between basal and tillering fertilization, 20 days after tillering fertilization and 9 days after panicle fertilization were the critical periods to control nitrogen loss from paddy field. After the urea application, DTN was the main part of the nitrogen in surface water of paddy field, and inorganic nitrogen (IN) was the major component in DTN, while NH₄⁺-N accounted for more than 64.0% of IN. The concentrations of TN, DTN and NH₄⁺-N in the critical periods for controling N loss during rice growth period were studied. Compared with T1, the concentrations of these 3 forms of nitrogen were decreased by 2.9%, 1.6%, 3.1% respectively in T2, decreased by 15.5%, 14.7%, 22.3% respectively in T3, and decreased by 16.1%, 22.9%, 34.1% respectively in T4. Considering the rice grain yield, T3 was determined to be the effective measure, as it could ensure rice grain yield and meanwhile effectively reduce the risk of nitrogen loss from paddy field.