Growth Characteristics, Carbon And Nitrogen Metabolism, And Nutrient Absorption In Castor Plants Grown In Medium Saline Soil

The field study was done in the medium saline soil on Xinyang Farm, Sheyang County, Jiangsu Province during two castor growing seasons from2011to2012. With Zibi8as the tested variety, growth characteristics, carbon and nitrogen metabolism, and nutrient absorption in castor plants grown in medium saline soil were studied under different treatments of nitrogen and phosphorus applied amount. The results were as follows:1. Growth characteristics and grain yield on medium saline soilPlant height increased at a low rate at seedling stage and a high rate at budding stage and flowering stage. At the flowering and fruiting stage, the rate of plant height declined. The different applied amount of nitrogen and phosphorus had no significant effects on the number of true main-stem leaves. The dry matter of stems and leaves accumulated slowly during the seedling stage. In budding stage, the dry matter increased rapidly, and reached a peak at flowering stage. However, the dry matter accumulation slowed down after fruiting stage. The dry matter of inflorescence increased gradually, and the highest accumulation rate was determined at fruiting stage. The dry matter in flowering, fruiting and grain filling and ripening stage was in significantly positive linear correlation with grain yield. The different nitrogen and phosphorus applied amount had significant effects on castor growth. The treatment fertilized with225kg·hm-2N and90kg-hm"2P205had the highest grain yield of3568.4kg·hm-2.2. Carbon and nitrogen metabolism in castor plants grown in medium saline soilLeaf SPAD readings were in significant positive linear correlation with leaf nitrogen content. The SPAD readings gradually increased from seedling stage to budding stage, and reached a peak in budding stage comparing the whole growth period. From budding stage to fruiting stage there was a trend of slow decline in SPAD readings, however it increased again at grain filling and ripening stage. Applying appropriate amount of nitrogen and phosphorus, soluble sugar content in the leaves and stems was high at early stages, and decreased significantly after flowering stage. From seedling stage to flowering and fruiting stage, the leaf soluble protein content increased slowly and continuously, and declined at grain filling and ripening stage. The stem soluble protein content gradually increased from seedling stage to budding stage, and declined from budding stage to flowering, and increased again at grain filling and ripening stage. The total soluble protein content in grains increased generally with the growth period. The treatment with N225kg·hm"2and P2O590kg·hm-2could not only benefit the increase in leaf SPAD readings, and accumulation of leaf nitrogen, soluble sugar and soluble protein, it could also have advantages in nutrient transfer from leaves and stems to flowers and grains at late growth periods, and the grain soluble sugar transformation which could improve grain weight.3. Absorption and Utilization of Nutrients in Castor Plants Grown in Medium Saline Soil along Coastal LineThe amount and rate of nitrogen, phosphorus, and potassium absorption was in conformity with a "slow-fast-slow-fast" style, with its peak at flowering stage. The applied amount of nitrogen and phosphorus and their interaction produced effects on the absorption of nitrogen, phosphorus, and potassium in different plant organs and the whole plant at the probability of0.01. The biggest absorption amount of nitrogen, phosphorus, and potassium were determined when nitrogen was applied at225kg·hm-2and phosphorus at90kg·hm-2. In this treatment,5.88kg N,2.24kg P2O5and8.84kg K2O were needed to produce100kg castor bean. The applied amount of nitrogen and phosphorus and their interaction also produced effects on the use efficiency of nitrogen, phosphorus, and potassium for grain production at the probability of0.01. The use efficiency of nitrogen, phosphorus, and potassium for grain production in the treatments with high grain yield was at the medium and high levels among all the treatments, indicating that there was a contradiction between the increase of grain yield and the use efficiency for grain production.