氮磷调控及紫云英配施提高早稻冠层特性和产量

Regulation of nitrogen-phosphorus and Chinese milk vetch improve canopy characteristics and yield of early season rice

为揭示不同氮、磷施用量及配合翻压适量紫云英入田对早稻冠层特性和产量的影响，在7个施氮、3个施磷及2个不施氮/磷水平下，开展早稻全生育期叶面积指数LAI、冠层光合有效辐射PAR传输特性、叶片叶绿素SPAD 值、生育后期剑叶净光合速率 Pn及产量的试验观测。结果表明，氮磷调控可显著影响早稻 LAI、叶片叶绿素含量和叶片光合速率，进而通过调节LAI影响冠层PAR传输特性，最终表现为产量上的差异。缺氮对早稻的影响显著高于缺磷，但在施肥充足时，磷肥对产量的影响比氮肥更加显著。早稻冠层特性和产量随氮、磷施用量的增加表现出边际递减效应，当施用量超过某一值时出现拐点，最终表现为产量的下降。在赣抚平原灌区，187.5～225 kg/hm2施氮量和60～120 kg/hm2施磷量以及翻压15000 kg/hm2紫云英鲜草入田可有效提高早稻LAI和冠层PAR截获率In以及叶片叶绿素含量，维持剑叶生长期内较高的净光合速率Pn，获得高产。

Fertilization was an essential agricultural practice to improve soil fertility and quality, and the change leaf area index （LAI） and plant chlorophyll content, and had a direct effect on photosynthetic carbon assimilation and grain yield. In order to reveal the effect of a nitrogen-phosphorus fertilizer regulation and the ploughing down of Chinese milk vetch planted in the winter on the canopy characteristics and yield of early season rice, experiments were carried out, with 7 nitrogen levels （including 2 combined applications of chemical nitrogen and green manure levels） and 3 phosphorus levels and 2 No-nitrogen / phosphorous levels. LAI, the transmission characteristics of canopy photosynthetically active radiation （PAR）, and leaf SPAD values were measured during the whole growth period, and the leaf net photosynthetic rate （Pn） was also measured in the heading-flowering period and in the grain-filling period, and the yield of early season rice was measured after harvesting. The results showed that nitrogen and phosphorus fertilizer could significantly affect the LAI which had a direct effect on light transmission and interception, SPAD value, Pn, and yield. In a certain range, increasing nitrogen fertilizer could cause a higher LAI, significantly, while increasing phosphorous fertilizer also changed the LAI in a slightly elevated but not significant manner. The variation trend of the canopy PAR interception and the LAI were basically the same, while the canopy PAR transmittance was the opposite. However, the effect of the LAI on reflectance was not obvious enough, its values, greatly influenced by mirror reflection, maintained between 3%~5%. With an increase of chemical fertilizer, the marginal diminishing effect gradually came into play. When the chemical fertilizer was overdosed, especially when the nitrogen fertilizer was higher than 225 kg/hm2 or the phosphate fertilizer higher than 120 kg/hm2, the effect curve appeared at an inflection point, and the early season rice growth might be inhibited and the grain yield would be cut. Ploughing down of moderate green manure （Chinese milk vetch） planted in the winter could significantly promote the LAI, light transmission, and interception, SPAD, photosynthesis, and yield under the same fertilizer, especially in the condition of low nitrogen. This could be because ploughing down green manure could increase the soil organic matter, soil humus, and soil microbial quantity and activity, and effectively reduce the fixation on nutrients. Available nutrients were released in spurts, and the soil nitrogen update was accelerated. An adequate soil nitrogen supply was conducive to maintaining the chlorophyll content of flag leaves, prolonging the functional period of leaves, and improving the photosynthesis efficiency and yield. The effects of a phosphorus deficiency on leaves were significantly less than that of low nitrogen availability, although phosphorus was limited to the promotion of chlorophyll content. A reasonable increase of phosphorus fertilizer could affect crop yield by promoting the LAI, light interception, and photosynthesis efficiency. This study considered that, in the Ganzhou and Fuzhou Plain Irrigation District, a combined application of 187.5~225 kg/hm2 nitrogen, 60~120 kg/hm2 phosphorus, and 15000 kg/hm2 Chinese milk vetch effectively improved the LAI, canopy PAR interception, and the content of chlorophyll, maintained a higher net photosynthesis efficiency, and consequently, enriched crop yield. It should be pointed out that, because of the limited manpower and material resources, this paper involved only one rice variety and one year’s data, and the research on photosynthesis was only limited to the leaf scale, and in the measurement of PAR transmission characteristics and photosynthesis there existed a certain time lapse. Further studies are required to research the effect of different amounts of ploughing down of Chinese milk vetch on early season rice canopy characteristics.