根区水质模型在黄土高原旱区冬小麦氮肥管理中的适用性分析

摘要

Luxurious and improper application of nitrogen (N) is an obvious problem on the Loess Plateau. Employing a crop model to explore an optimal N fertilizer management for local farmers is an effective research method. In the present study, we firstly selected a continuous eight-year winter wheat-spring maize experiment (from 2004 to 2011) and a two-year winter wheat N fertilizer experiment (from 2010 to 2012) to calibrate and validate root zone water quality model (version 2, RZWQM2) aiming to assess the adaptability of this model on the Loess Plateau. We set up the following 8 scenarios of N application rate of base fertilizer for winter wheat in the RZWQM2:0, 30, 60, 90, 120, 150, 180 and 210 kg/hm2 aiming to search for proper N application rate of the base fertilizer. Based on the proper N application rate (90 kg/hm2 in this study) of base fertilizer, we also set up the following 5 scenarios of N application rate with the ratio of base to topdressing in the RZWQM2:5:1, 5:2, 5:3, 5:4 and 5:5 in wheat turning green, jointing and heading stages, respectively. In this way, we aimed to search for the best N topdressing stage and the proper N topdressing rate for winter wheat. The calibrated and validated RZWQM2 was used to characterize the respond of winter wheat yield, water use efficiency (WUE), N uptake of grain and N harvest index to the different N application rates and timings based on the long historical meteorological data (from 1956 to 2012). The results demonstrated the capability of the RZWQM2 to efficiently simulate crop growth, water movement (100 cm depth), and final crop yield in the different rainfall year on the Loess Plateau;meanwhile, RZWQM2 effectively simulated the yield and N uptake of winter wheat under different N application method. Both of the results provided a solid basis for the application of RZWQM2 to study the N fertilizer management on the Loess Plateau. In the simulations, the wheat yield, WUE and N uptake of grain increased fast before the base N fertilizer of 90 kg/hm2 and slowly afterwards. The N harvest index in the wet year increased with the N application rate of base fertilizer and was stable after the N application rate of 180 kg/hm2;it maintained a high level when the N application rate of base fertilizer was between 90 and 180 kg/hm2 in the medium year, as well as between 60 and 150 kg/hm2 in the dry year. Thus, the single base N fertilizer of 120-150 kg/hm2 could adequately satisfy the need of wheat growth in the dryland of the Loess Plateau in different rainfall years. The optimal topdressing stage of N fertilizer was between turning green and jointing stage because of the high wheat yield. On the basis of base N fertilizer of 90 kg/hm2, the wheat yield, WUE and N uptake of grain increased with the topdressing amount in the turning green stage;the N harvest index in the wet year always increased with the N topdressing rate;the N harvest index peaked in the medium year on the topdressing N rate of 36 kg/hm2 and in the dry year on the topdressing N rate of 18 kg/hm2. We found topdressing N rate of 54-72, 36-54, and 18-36 kg/hm2 respectively in the wet, medium and dry year could satisfy the need of high wheat yield and maintain high level of N harvest index. These findings provide some useful guidance for local farmers to optimize their N fertilizer management. More field experiments need to be conducted to verify the conclusions of this study in the future.%为利用作物模型模拟寻找田间尺度上合理的氮肥管理措施，该研究利用黄土高原旱区多年冬小麦-春玉米轮作试验（2004－2011）和两年冬小麦施肥试验（2010－2012）对根区水质模型（root zone water quality model-version 2，RZWQM2）进行率定和验证，验证该模型在当地的适用性；并结合当地56 a历史气象数据，利用模型模拟研究旱区冬小麦在不同降水年型下最佳氮肥管理模式。结果表明 RZWQM2在不同降水年型下均可以较好地模拟黄土高原旱区作物生长发育、产量指标和土壤水分的动态变化，并且能够较好地模拟不同施肥方式下冬小麦的产量和氮素指标；黄土高原旱区120～150 kg/hm2（以 N 计）的底肥基本可以满足不同降雨年型下冬小麦稳产高产的需要；冬小麦单次追肥的最佳追肥时期为返青期至拔节期；在90 kg/hm2底施氮肥的基础上，丰水年54～72 kg/hm2的追氮量，平水年36～54 kg/hm2的追氮量，干旱年18～36 kg/hm2的追氮量，不但可以满足冬小麦高产的要求，并且维持氮素收获指数在较高水平。