重庆地区油菜收获后单作竹豆适宜播期和翻埋期的研究

在重庆地区,选择夏季豆科绿肥作物竹豆为研究对象,设置3个播期(间隔5d)与3个翻压期(间隔15d),测定了不同生育期竹豆的地上/地下干物质和养分含量;采取尼龙袋法测定不同翻压期竹豆干物质和氮磷钾等养分的腐解速率;同时测定了竹豆翻埋后土壤速效养分含量的变化情况。结果表明,播期与翻压期显著影响单作竹豆生物量及养分含量。随着播期的推迟,地上部干重显著下降,根冠比早期下降,后期有增加趋势。推迟播种时,植株全氮含量在生育后期整体高于对照。植株全磷含量不同时期变化趋势不同,全钾含量推迟播种后整体表现出显著下降的趋势。翻埋后,不同播期植株干物质及养分降解速率变化趋势基本一致,翻压期推迟15d时的干物质、全氮、全磷及全钾残留率均显著高于对照。随着翻埋时间的延长,土壤碱解氮含量整体呈增加趋势,而土壤速效钾和速效磷含量不同时期存在差异。综合分析认为,在重庆地区单作竹豆应在前茬油菜收获后推迟10d播种,翻压时间宜在8月初。

A study of the optimum sowing and burial dates of rice beans used as green manure after canola harvest in the Chongqing region

Rice bean (Phaseolus calcaratus) is an important summer green manure crop for improvement of soil quality. In the current study, rice bean was sown on three dates (May 2, May 7, and May 12) and was ploughed in soil on August 4, August 18 or September 2 in Chongqing, China (9 treatments; 3 replicates). Data collected included the above- and below-ground biomass, the plant nutrient contents at different growth stages, the decay rate of matter after burial using a nylon bag method, and levels of soil available nutrients (N, P, and K) after the rice bean was buried. With later sowing dates, the aboveground biomass was significantly decreased, while the root∶shoot ratio was reduced with earlier sowing, but tended to be increased with later sowing. Delayed sowing increased the rice bean plant total nitrogen (TN) content when compared with the control. Plant total potassium (TK) content was significantly reduced by delayed sowing date, whereas differences between sowing dates for total phosphorus (TP) showed no consistent pattern. Dry matter decay rate and plant nutrient levels showed similar trends for the different sowing dates. The values for residual dry matter in nylon bags, TN, TP, and TK were significantly higher than those of the control when the burial date was delayed 15 days in August. After the rice bean was buried, soil available N levels increased during the 21 days, whereas soil available K and P levels were variable. Because of the higher rice bean biomass and nutrient contents from earlier sowing, 10 days after canola harvest is the recommended sowing date for rice bean in Chongqing. The burial date should be in early August, when temperatures are still high enough for the buried plant material to decompose.