Simulation of nitrate leaching under potato crops in a Mediterranean area. Influence of frost prevention irrigation on nitrogen transport

The Sa Pobla area (Majorca Island, Spain) heavily depends on the use of groundwater resources for irrigation and urban water supply and is characterised by the presence of intensive potato farming activities. The Plioquaternary aquifer is unconfined and contains high levels of nitrate concentrations. To analyse the risk of contamination to the aquifer arising from agricultural practices, the amount of water and nitrogen leached below the root zone was simulated by the GLEAMS code. Data for model calibration and validation were obtained from field experiments on six potato crops for the years 2004-2007.When air temperatures drop below 1 °C irrigation water is applied to prevent crops from frost damage. During times of anomalously low air temperatures, the risk of nitrate leaching is increased by as much as 318% from frost prevention irrigation under normal local conditions.The GLEAMS simulation model was successfully calibrated for Sa Pobla conditions under potato cropping as shown by RMSE values for the water transport module of 0.19, 0.14 and 0.13 for the calibration period and 0.20, 0.25 and 0.15 for the validation period at depths of 0.3, 0.6, and 0.9 m respectively; and for the chemical transport module the R² value was 0.82 for the calibration period and 0.60 for the validation period. Consequently, for Sa Pobla conditions, GLEAMS can be used to assess the effectiveness of different agricultural management practices to reduce nitrate leaching. It was concluded that additional irrigation water applied for frost prevention plays a very important role in nitrate leaching below the root zone, which enhances the nitrogen loading to the aquifer.     

农田土壤中土壤水渗漏与硝态氮淋失的模拟研究

应用HYDRUS-1D模型对黄淮海平原的主要土壤(黄潮土和风沙土)中水分与硝态氮的垂直运移规律进行了模拟分析。对模型参数的敏感性分析表明:饱和水力传导度是最敏感的参数,饱和含水量的敏感性次之。数值模拟结果表明:该地区在传统水氮管理制度下,土壤水渗漏和硝态氮淋失非常严重;全耕作年风沙土的土壤水渗漏大于黄潮土,分别为34.3cm和22.7cm,占灌水量的42.1%和74.6%;风沙土的硝态氮淋失大于黄潮土,分别为108.0kg/hm和76.6kg/hm,占总输入氮量的25.3%、14.3%。     

Policy incentives for reducing nitrate leaching from intensive agriculture in desert oases of Alxa, Inner Mongolia, China

Excessive irrigation and nitrogen applications result in substantial nitrate leaching into groundwater in intensively cropped oases in desert areas of Alxa, Inner Mongolia. An integrated modelling approach was developed and applied to compare policy incentives to reduce nitrate leaching. The integrated model consists of a process-based biophysical model, a meta-model, a farm economic model and an assessment of policy incentives. The modelling results show that there are “win-win” opportunities for improving farm profitability and reducing nitrate leaching. We found that 4471 Yuan ha⁻¹ of farm gross margin could be obtained with a reduction in nitrate leaching of 373 kg ha⁻¹. Farmers’ lack of knowledge about water and nitrogen in soil, and on crop requirements for water and nitrogen could explain the differences, so that agricultural extension is an appropriate policy incentive for this area. When the economic optimum is obtained reductions in nitrate leaching are not achievable without profit penalties and there is a “trade-off” relationship between farm profitability and groundwater quality protection. The combination of low elasticity of nitrate leaching and large elasticity of farm gross margin against water price increases results in very high costs for reducing nitrate leaching (105.6 Yuan kg⁻¹). It is suggested that if the water price increases were coupled with subsidies for adopting nitrate leaching mitigation practices, environmental gains could come at a lower cost.     

北运河流域典型区污灌条件下氮素渗漏模拟及灌溉模式优选

为了揭示北运河流域农田氮素的渗漏迁移特征,为该流域水资源总体规划和非点源污染综合整治提供指导,以北运河流域武清区为研究对象,采用改进的SWAT模型对16种不同灌溉模式下农田氮素的渗漏特征进行模拟分析。结果显示,随着污灌次数的增加,氮素渗漏量也相应增加,但3次以下污灌,其变化不明显。在污灌次数相同,且连续污灌或者污灌间隔...     

Root growth, available soil water, and water-use efficiency of winter wheat under different irrigation regimes applied at different growth stages in North China

Field experiments were conducted at the Luancheng Agro-Ecosystem Experimental Station of the Chinese Academy of Sciences during the winter wheat growing seasons in 2006-2007 and 2007-2008. Experiments involving winter wheat with 1, 2, and 3 irrigation applications at jointing, heading, or milking were conducted, and the total irrigation water supplied was maintained at 120 mm. The results indicated that irrigation during the later part of the winter wheat growing season and increase in irrigation frequency decreased the available soil water; this result was mainly due to the changes in the vertical distribution of root length density. In ≤30-cm-deep soil profiles, 3 times irrigation at jointing, heading, and milking increased the root length density, while in >30-cm-deep soil profiles, 1 time irrigation at jointing resulted in the highest root length density. With regard to evapotranspiration (ET), there was no significant (LSD, P < 0.05) difference between the regimes wherein irrigation was applied only once at jointing; 2 times at jointing and heading; and 3 times at jointing, heading, and milking. Compared with 1 and 3 times irrigation during the winter wheat growing season, 2 times irrigation increased grain yield and 2 times irrigation at jointing and heading produced the highest water-use efficiency (WUE). Combining the results obtained regarding grain yield and WUE, it can be concluded that irrigation at the jointing and heading stages results in high grain yield and WUE, which will offer a sound measurement for developing deficit irrigation regimes in North China.