| The study was conducted on the Experimental Farm of Yangzhou University and Jiangsu Sheyang Salt Work during three castor growing seasons from 2007 to 2009. In a seedling tray and pot transplantation experiment conducted on the Experimental Farm of Yangzhou University, castor seedlings were first cultured in plastic seedling trays containing organic matter-soil mixture at different salinity levels, and then transplanted into pots containing conventional soils at similar salinity levels. Emergence, survival, seedling growth, and leaf photosynthetic parameters were determined. In a field experiment conducted on medium saline soil at Jiangsu Sheyang Salt Work, the effects of planting density and nitrogen application amount on the growth characteristics and nutrient absorption of castor plant were studied. The main results were as follows.1. Responses of Castor Plant to Salinity Stress at Seedling StageCastor bean (Ricinus communis L. ) is usually grown on marginal land that can be prone to having medium to high salt concentrations. This experiment was done to identify a salinity threshold level for castor bean emergence and stand establishment. Castor bean seedlings were first cultured in plastic seedling trays containing organic matter-soil mixture at different salinity levels (3, 6, 9 and 12 g NaCl per kg dry seedling media), and then transplanted into pots containing conventional soils at similar salinity levels. Emergence, survival, seedling growth, and leaf photosynthetic parameters were determined. At the 0.6% salinity level or less, emergence rate reached 70.0% or higher, survival rate after transplantation reached 80.0% or higher. Seedling growth and leaf photosynthetic parameters, including the growth of cotyledon and true leaves, the fresh weight and dry weight of castor plant, root growth, chlorophyll content and photosynthesis, were not severely affected. As the salinity in the seedling media increased to 0.9% and 1.2%, seedling growth and leaf photosynthetic parameters were significantly affected. Photosynthetic rate was reduced by 46.9% and 66.3%, SPAD reading decreased by 21.6% and 24.1%, stomatal conductance decreased by 58.3% and 65.5%.2. Impact of Planting Density and Nitrogen Application Amount on Growth and Development and Yield on Medium Saline SoilPlanting density and nitrogen application amount are two critical factors affecting castor plant growth, development, and yield. The effects of planting density and nitrogen application amount on growth and development characteristics, dry matter accumulation and distribution and yield were studied. The height of castor plant, stem true leaf number, and dry matter were slowly increased before flowering, and rapidly increased after flowering stage. High dry matter accumulation rate at flowering stage was beneficial to the transport of nutrients from the leaves to the reproductive organs such as inflorescences and the exchange from vegetative growth to reproductive growth. Too high rate of dry matter accumulation of plants at flowering stage is likely to cause excessive growth, which was not beneficial to the transport of nutrients from leaves to inflorescence. Under our experimental conditions, the highest yield of Zibi 5 was 2360.51 kg·hm-2 when the planting density was 13 000 plant·hm-2 and nitrogen application amount was 120 kg·hm-2. The highest yield of Yunbi TCO-202 was 3483.36 kg·hm-2 under the treatment of density 16 000 plant·hm-2 and nitrogen application amount 120 kg·hm-2.3. Impact of Key Cultural Measures on Nutrient Absorption and Utilization of Castor on Medium Saline SoilNitrogen, phosphorus and potassium are essential nutrients for castor plant growth and yield development. The absorption and utilization of nitrogen, phosphorus, and potassium in castor plants grown on medium saline soil were studied at different growth stages. The accumulation rates of nitrogen, phosphorus, and potassium were low prior to flowering, but increased rapidly after flowering. Both the absorption rate and the absorption amount of nitrogen, phosphorus, and potassium of Zibi 5 reach their peak values at flowering stage. Under the conditions of planting density 13 000 plant·hm-2 and nitrogen application amount 120 kg·hm-2, the yield of Zibi 5 was the highest. Under these field conditions, 9.93-10.33 kg nitrogen, 1.23-1.35 kg phosphorus, 9.55-11.30 kg potassium were needed to produce 100 kg castor seed. Similar trends were found in the absorption characteristics of nitrogen and phosphorus in Yunbi TCO-202, but the absorption of potassium demonstrated a trend of"fast - slow - fast". Under the conditions of planting density 16 000 plant·hm-2 and nitrogen application amount 120 kg·hm-2, the yield of Yunbi TCO-202 was the highest. 8.25-10.12 kg nitrogen, 1.10-1.13 kg phosphorus, and potassium 9.22-11.16 kg were needed to produce 100 kg castor seed. |
