摘要：
A field microplot experiment was conducted in the red soil hilly region of South China to evaluate plant phosphorus (P) uptake under soybean and citrus monoculture and the soybean-citrus intercropping system using the 32p tracer technique.P fertilizer was applied at three depths (15,35,and 55 cm).The experimental results showed that the planting pattern and 32p application depth significantly affected the characteristics of P uptake by soybean and citrus.Under the soybean-citrus intercropping system,considerable competition was observed when the 32p fertilizer was applied to the topsoil (15 cm);therefore,the 32p recovery rate declined by 41.5% and 14.7% for soybean and citrus,and 32p supplying amount of topsoil to soybean and citrus decreaeed by 346.8 and 148.1 mg plot-1,respectively,compared to those under the monoculture.However,32 p recovery of soybean was promoted when 32p fertilizer was applied to the deeper soil layers (35 and 55 cm) under soybean-citrus intercropping.Under the soybean monoculture,32p fertilizer could hardly be used by soybean when 32p fertilizer was applied at the 55 cm depth or below,with the recovery rate being less than 0.1%;it was up to 0.253% by soybean under intercropping.The higher P recovery of soybean under soybean-citrus intercropping when P was applied in the deeper soil layers was because part of the P nutrient that the citrus absorbed from the deeper soil layers could be released into the topsoil and then it could be used by the soybean.
作者机构：
[Xie G.; Rong X.; Liu Q.; Peng J.] College of Resources and Environment, Hunan Agricultural University, Changsha 410128, China;[Zheng S.] Soil and Fertilizer Institute of Hunan Province, Changsha 410125, China;Changsha Environmental Protection Colleges, Changsha 410004, China;[Liao Y.] College of Resources and Environment, Hunan Agricultural University, Changsha 410128, China, Soil and Fertilizer Institute of Hunan Province, Changsha 410125, China;[Fan M.] College of Resources and Environment, Hunan Agricultural University, Changsha 410128, China, Changsha Environmental Protection Colleges, Changsha 410004, China
通讯机构：
[Xiangmin Rong] C;[Shengxian Zheng] S;College of Resources and Environment, Hunan Agricultural University, Changsha, China<&wdkj&>Soil and Fertilizer Institute of Hunan Province, Changsha, China
摘要：
Radishes (Raphanus sativus L.) were grown in plastic pots in a screenhouse to investigate the influences of nitrogen fertilizer application rates (NFAR) on yield, nitrate content, nitrate reductase activity (NR), nutrition quality, and nitrogen recovery efficiency (NRE) at commercial mature stage. Five N-rate treatments, 0.644, 0.819, 0.995, 1.170, and 1.346 g·pot−1, were set up in the screenhouse pot experiments, and nitrogen fertilizer (unlabeled N and 15N-labeled fertilizer) was applied as basal dressing and topdressing, respectively. The results indicated that the fresh and dry weight yields of radish increased with the increase of NFAR at the range of 0.099 to 0.180 g N·kg−1 soil, decreased at 0.207 g N·kg−1 soil, and accordingly there was a significant quadratic relationship between the fresh and dry weight yields of radish and the NFAR. At the high addition of urea-N fertilizer, the nitrate content accumulated in the fleshy roots and leaves due to the decline in NR activity. From 0.644 to 0.819 g N·pot−1 NR increased most rapidly, the highest NR activity occurred at 0.819 g N·pot−1, and the lowest NR activity happened at 1.346 g N·pot−1. Soluble sugar and ascorbic acid initially increased to the highest value and then decreased, and, contrarily, crude fiber rapidly decreased with the increase of NFAR. Total N uptake (TNU), N derived from fertilizer (Ndff), and N derived from soil (Ndfs) in radish increased, except that Ndfs relatively and slightly decreased at the rate of 0.207 g N·kg−1soil. The ratio of Ndff to TNU increased, but the ratio of Ndfs to TNU as well as NRE of N fertilizer decreased with the increase of NFAR. Therefore, the appropriate NFAR should be preferably recommended for improving the yields and nutrition qualities of radish and NRE of N fertilizer.
