海南岛主要作物氮肥定额及区域农田氮素承载力研究

Nitrogen application quota for major crops and nitrogen carrying capacity of cropland in Hainan Island

【目的】针对海南当前作物氮肥投入高、养分损失大、利用效率低等问题,基于养分平衡原理,测算协同满足作物增产和环境安全双目标下的主要作物氮肥投入上限及区域农田氮素承载力,并提出氮素调控措施。【方法】根据大样本农户调研结果明确作物产量潜力,通过自测数据和收集的国际粮农组织(FAO)信息、文献,构建作物产品氮浓度数据库及华南地区作物优化管理条件下的氮素盈余数据库,基于养分平衡原理评估作物高产下的氮素需求、氮素盈余阈值和氮肥定额。结合种植结构信息,定量海南区域农田氮素承载力。【结果】海南粮食(以水稻为例)、蔬菜作物的平均产量分别为6.2、33.9 t/hm^(2),分别低于全国产量水平13%和32%,水果作物的平均产量为33.6 t/hm^(2),与全国产量水平一致;华南地区粮食、蔬菜、水果作物的氮素盈余阈值分别为81、108和283 kg/hm^(2);粮食作物氮肥定额平均为160 kg/hm^(2),减量潜力平均为21%,蔬菜氮肥定额范围为181~476 kg/hm^(2),减量潜力平均为22%,其中豇豆减量潜力最大,为39%,水果氮肥定额范围为240~689 kg/hm^(2),减量潜力平均为28%,其他经济作物氮肥定额范围196~306 kg/hm^(2)。海南各市县的区域农田氮素承载力在0.4~2.8万t,最高的是乐东(2.8万t),白沙和五指山最低(0.4万t)。当前海南农田总体氮素投入高于承载力33%,而氮素产出低于产出潜力48%,氮素盈余高于盈余阈值156%,海南作物系统当前氮素利用率为23%,低于目标氮素利用效率37个百分点。【结论】海南粮食、蔬菜作物产量水平低于全国产量水平,水果作物产量水平与全国产量水平一致。经济作物的氮素盈余阈值偏高导致其氮肥定额偏高,主要由于当前经济作物的氮肥管理并未充分实行全要素协同优化。海南当前区域农田氮素输入已超出安全承载力,特别是海口、临高、儋州、万宁等经济作物占比较高的市县。未来海南氮肥管理应重视经济作物上的氮肥减量增效技术的应用,进一步降低经济作物的氮素盈余阈值,并优化经济作物的氮肥定额,同时应提升有机肥替代化肥的比例。

【Objectives】The crop production in Hainan Island is challenged by excessive nitrogen fertilizer input,high nitrogen loss,and low nitrogen utilization efficiency.Guided by the principle of nutrient balance,we determined the maximum nitrogen fertilizer input for major crops and the regional nitrogen carrying capacity,ensuring a balance between increased crop yields and environmental safety.Additionally,we will propose optimization measures for nitrogen fertilizer management.【Methods】We conducted an extensive survey among farmers to determine crop yield potential.Following this,we established databases of nitrogen concentrations in crop products and optimal nitrogen surplus levels under optimal crop management conditions in South China.These databases were meticulously crafted using self-measured data,information from the Food and Agriculture Organization(FAO) statistics,and published literature.Subsequently,we evaluated nitrogen requirements,surplus thresholds,and nitrogen fertilizer quotas under conditions conducive to high yields,all based on the principle of nutrient balance.Additionally,we quantified Hainan's regional-scale nitrogen capacity by integrating this information with the local cropping structure.【Results】The average yields of grain(rice,for example) and vegetable crops in Hainan were 6.2 and 33.9 t/hm^(2),which were 13% and 32% lower than the national yield,respectively.However,the average yield of fruit crops was 33.6 t/hm^(2),which was consistent with the national yield level.The nitrogen surplus thresholds for grain,vegetable,and fruit crops in South China were81 kg/hm^(2),108 kg/hm^(2) and 283 kg/hm^(2),respectively.The average nitrogen application quota for grain crops was160 kg/hm^(2),which represented a potential reduction in nitrogen application of 21%,compared to current levels.For vegetable crops,the nitrogen application quota ranges from 181 kg/hm^(2) to 476 kg/hm^(2),with a general potential reduction of 22%,and the greatest potential reduction of 39% in legume crops.The nitrogen application quota range for fruit crops was 240-689 kg/hm^(2),with a potential reduction of 28%.The nitrogen application quota range for other economically important crops was 196-306 kg/hm^(2).The regional nitrogen carrying capacity of farmland in Hainan cities and counties ranged from 4 kt to 28 kt,amony them,Ledong had the highest capacity(28 kt),Baisha and Wuzhishan had the lowest carrying capacity(4 kt).Currently,the region's nitrogen input is 33%higher than the carrying capacity,but the output is 48% lower than the target,the nitrogen surplus exceeds the target by 156%,and the current nitrogen use efficiency is 23%,which is lower than the target by 37 percentage points.【Conclusions】The yield level of Hainan's grain and vegetable crops is lower than the national yield level,but the yield level of fruit crops is in line with the national yield level.The high nitrogen surplus thresholds for economic crops result in elevated nitrogen fertilizer quotas,primarily because the current nitrogen fertilizer management for economic crops does not fully implement the optimization of all principles.Hainan's current regional nitrogen input has exceeded its safe carrying capacity,particularly in cities and counties with a high proportion of economic crops such as Haikou,Lingao,Danzhou,and Wanning.In the future,nitrogen fertilizer management in Hainan should prioritize researching techniques to reduce nitrogen intensity and enhance efficiency especially for economic crops,while also optimizing their nitrogen surplus thresholds and fertilizer quotas,and the proportion of organic fertilizers replacing chemical fertilizers should be increased.