关键词: 长期施肥, 红壤, 不同形态氮素, 迁移, 水稻

Abstract:

【Objective】 This study was aimed to explore the characteristics of different nitrogen forms migration under different fertilizations in typical red soil, so as to provide theoretical basis for rational amount of applied nitrogen in red soil region. 【Method】 Based on the long-term experiment site located at Jinxian, Jiangxi province, four typical treatments were chosen as: (1) no fertilization (CK); (2) mineral nitrogen, phosphorus, potassium (NPK); (3) NPK combined with straw (NPKS); (4) NPK combined with pig manure and straw (NPKSM). Four levels of soil samples of 0-10 cm, 10-20 cm, 20-40 cm and 40-60cm were collected from each treatment. Soil total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), nitrate nitrogen (NO₃ ^--N), ammonium nitrogen (NH₄ ⁺-N), dissolved organic nitrogen (DON) and microbial biomass nitrogen (SMBN) were measured and analyzed. 【Result】 The results showed that the content of nitrogen forms under different treatments decreased with soil depth, while the different nitrogen forms demonstrated different characteristics in different soil layers. The available nitrogen forms (e.g. AN, NO₃ ^--N, NH₄ ⁺-N, DON and SMBN) were concentrated at 0-20 cm soil layers, and their content obviously decreased in 20-60 cm compared with 0-20 cm under all treatments. The TN content in 0-40 cm layers was no significantly change. The fertilizer treatments (i.e. NPK, NPKS and NPKSM) could improve all nitrogen forms content compared with CK, which was the highest under NPKSM treatment. The TN content was little change under the same treatment in 0-40 cm, while the TN content was ordered as NPKSM>NPKS>NPK>CK in 0-60 cm. The AN content under the same treatment was obviously decreased with soil depths. Therein, compared with the AN content in 10-20 cm, which in 20-40 cm was decreased by 42% (CK), 50% (NPK), and 44% (NPKS, NPKSM), respectively. The NO₃ ^--N and NH₄ ⁺-N content were highest under NPKSM treatment in each soil layers. Therein, the drop of NH₄ ⁺-N between 40-60 cm and 0-10 cm was higher than that of NO₃ ^--N, which ordered as 54% (NPKS)>51% (CK)>48% (NPK)>36% (NPKSM). The DON content was significantly different among the treatments in 0-20 cm, and which was higher under the treatment with mineral fertilizer combined with organic fertilizer. The DON content under CK and NPK treatments in 40-60 cm was increased slightly, while significantly decreased under NPKS and NPKSM treatments. The SMBN was significantly different among treatments in 10-20 cm layer compared with other soil layers, and ordered as NPKSM>NPKS>NPK>CK. The proportion of each form of nitrogen to total nitrogen was decreased with soil depth. There was significantly positive correlation between TN, AN, NO₃ ^--N, DON and SMBN at 0-20 cm (P≤0.05), among which TN, DON, AN and SMBN existed very significant positive correlation (P≤0.01). The early, late rice grain yield, straw yield, total biomass, and their nitrogen accumulation were significantly higher under fertilization treatments (i.e. NPK, NPKS, and NPKSM) than that under CK treatment, which was the highest under NPKSM treatment. Moreover, the residual mineral nitrogen and apparent nitrogen loss were also highest under NPKSM treatment. 【Conclusion】 In red soil, the effect of fertilization on nitrogen form focused on the upper layer (e.g. 0-20 cm). All the nitrogen forms content under all treatments decreased with soil depths. All forms of nitrogen content at 0-60 cm was improved under NPKSM. Meanwhile, the crop yield and their nitrogen accumulation were significantly increased under NPKSM treatment, so did with the residual mineral nitrogen and apparent nitrogen loss.

Key words: long-term fertilization, red soil, various forms of nitrogen, migration, rice