Yields And Nitrogen Uptake Of Direct-Seeding Rice Cultivated In Aerobic Soil With Or Without Mulching

Shortage of water resource is one of the main inhibitors in development of sustainable agriculture. Since more than 80% of the freshwater used in agriculture finds its way in waterlogged rice soil, the traditional waterlogged way has been challenged by water-saving cultivation of rice crop. Thus, a novel cultivation system of rice crop in aerobic soil was found and it showed its great potential in water saving agriculture. In this system, about 90-100% of freshwater irrigated could be saved compared with waterlogged one.Rice seedlings are Usually transplanted to soil in this new cultivation system to ensure enough panicles per hectare. However, transplant would take more time and have less suviving rate of rice seedlings, compared with transplanted paddy rice. In our study, the method of direct-seedling was selected trying to overcome the disadvantages. The objective of the present study is to determine the effects of direct-seeding rice cultivated in aerobic soil with mulching on the rice growth and development, the yield formation and nitrogen uptake, so that we can provide a basis for nitrogen management practices for rice cultivation in aerobic soil condition.A two-year iield experiment was carried out in sandy loam soil in Yancheng, Jiangsu province (33 27'N, 120 11'E) in 2001 and 2002. There were three treatments in rice cultivation in aerobic soil, including the soil being covered with plastic film (PF), with rice straw (RS) and the soil without any mulching (B). The control for the experiment was the rice grown in waterlogged soil (W). The main field experiment, which was subdivided into one waterlogged area and one large aerobic area, was constructed in a one-factorial block design with three replications each treatment. The experimental block of waterlogged rice was separated from the aerobic block by a strong plastic foil vertically inserted into depth of 60 cm for hydrological isolation.After sowing, plastic film was used to cover all surface of aerobic treatments to ensure a better seedling emergence. At the 3-leaf stage, the plastic film was removed in RS and B treatments. The soil surface in RS treatment was then covered with semi-decomposed rice straw (about 6000 kg dry straw . hm-2). Two tensionmeters with tips at 18 cm depth were installed in each plot to indicate soil water content which was maintained round 75-90% of water holding capacity (WHC), that is to say, as soon as soil water content was lower than 75-90% of WHC, irrigation would be made immediately and then stopped when the water at the soil surface reached the expected values.15N sub-plots were laid out within each treatment and thus the application of225 kg N .hm-2 (15N-labeled urea with 2% 15N abundance ) was homogeneously added into soil by hand. Plant samples were taken in 15N sub-plots at four growth stages, such as maximum tillering, panicle initiation, heading and harvest of the rice plant. All the samples were dried at 70C for 72h after kept at 105C for 20 min to kill enzymes in the plants. Total plant N content and 15N abundance were determined with Delta C continuous flow mass spectrometer coupled to Carlo Erba elemental analyzer 1108 by Conflo II interface. Soil sampling at the depths of 0-20cm and 20-40cm from fields was done every two weeks during the experimental duration. The soil mineral N (including NO3--N and NH4+-N) was determined as follows: 0.01mol.L-1CaCl2 was used as extract on a horizontal shaker for Ih, and Nwm in the filtrate was analyzed using a flow-analyzer (CFAA3). At the same time the soil water content of each sample was determined by oven drying.The main results of this study are showing as follows. Grain yields of rice decreased slightly when cultivated in aerobic systems and the reduction rate ranged from 2%-18%. However, yields of upland rice plots covered with plastic film (PF) and straw mulch (RS) were 8% and 4% higher than that of upland rice without mulch (B). The havest index (HI) of rice crop had no significant differences between different treatments, and reduced when plant d...