中国栽培草地氮磷流动空间特征

【目的】中国畜牧业快速发展,对牧草需求日益增加,种植业结构调改已成为必然趋势。定量研究栽培草地的氮磷流动特征,可为优化牧草施肥和提高牧草产量提供科学依据。【方法】以苜蓿、黑麦草和燕麦草为研究对象,建立中国主要栽培牧草氮磷养分输入(输出)数据库,利用NUFER模型定量中国主要栽培牧草氮磷平衡账户、利用率和环境排放特征。【结果】(1)2014年,全国苜蓿、黑麦草和燕麦草草地氮输入(输出)总量分别为1 547、236和67 Gg,磷输入(输出)总量分别为323、44和16 Gg。单位面积苜蓿、黑麦草和燕麦草草地的氮输入(输出)量分别为326、427和217 kg N·hm~(-2),磷输入(输出)量分别为49、18和35 kg P·hm~(-2)。生物固氮是苜蓿草地氮的最主要输入项,占总输入量的51%,氮肥占黑麦草草地氮总输入量的93%,占燕麦草地总输入量的84%。磷肥是3种牧草磷的最主要输入项。(2)2014年,全国苜蓿、黑麦草和燕麦草的氮利用率分别为64%、93%和69%;磷利用率分别为28%、77%和34%。不同区域氮磷利用率差异很大。(3)2014年,单位面积苜蓿、黑麦草和燕麦草草地的氮环境排放量分别为23、4.0和9.9 kg N·hm~(-2),磷的环境排放量分别为2.6、3.8和2.6 kg P·hm~(-2)。西南地区苜蓿和黑麦草的氮磷环境排放量较高,西部各地区燕麦草草地氮磷环境排放量高于其他区域。(4)2014年,黑麦草草地氮呈亏缺态,其余栽培草地氮磷均有不同程度的盈余。中国西部地区苜蓿的土壤氮磷累积量高于东部地区;黑麦草的土壤氮磷累积量没有明显规律;青藏高原区燕麦草的土壤氮磷累积量大于其他区域。【结论】2014年,全国栽培苜蓿、黑麦草和燕麦草草地的氮磷输入(输出)量差异较大。生物固氮是苜蓿获取氮素的重要途径,田间管理需减少氮肥投入,燕麦和黑麦草主要通过化肥获取所需养分,应注重肥料施用。3种栽培牧草氮的利用率均高于60%,磷的利用率相对较低。黑麦草草地氮呈亏缺态,需增施氮肥,其余栽培草地氮磷均有不同程度的盈余,应控制肥料过多施用。

Spatial Characteristics of Nitrogen and Phosphorus Flow in Cultivated Grassland of China

【Objective】With the rapid development of animal husbandry in China and the increasing demand for forage, the adjustment of planting structure has become an inevitable trend. The objective of this study is to quantify the nitrogen (N) and phosphorus (P) spatial flow of cultivated forage, and to provide a scientific basis for increasing grassland productivity. 【Method】Taking alfalfa, ryegrass and oat grass as target forage species, the database of N and P input and output was established, the nutrient balance budgets, nutrient use efficiency and environmental emissions were quantified in cultivated grassland of China by using NUFER model. 【Result】 (1) In 2014, the total input (output) of N in alfalfa, ryegrass and oat grassland of China was 1 547, 236 and 67 Gg, respectively. The N input (output) of per unit area in alfalfa, ryegrass and oat grass grassland of China was 326, 427 and 217 kg N·hm^-2, respectively. The total input (output) of P in alfalfa, ryegrass and oat grass grassland of China was 323, 44 and 16 Gg and the P input (output) of per unit area was 49, 18 and 35 kg P·hm^-2, respectively. N fixation was the largest input item for alfalfa which accounted for 51% of the total N input into alfalfa grassland. N fertilizer was the largest input item for oat grass and ryegrass which accounted for 93% and 84% of the total N input into ryegrass and oat grass grassland, respectively. P fertilizer was the most important input of P in these kinds of forage. (2) In 2014, the nitrogen use efficiency (NUE) of alfalfa, ryegrass and oat grass grassland was 64%, 93% and 69%, respectively. The phosphorus use efficiency (PUE) was 28%, 77% and 34%, respectively. The NUE and pue varied greatly in different regions. (3) In 2014, the N loss of alfalfa, ryegrass and oat grass grassland per unit area was 23, 4.0 and 9.9 kg N·hm^-2 and the P loss of them was 2.6, 3.8 and 2.6 kg P·hm^-2, respectively. The N and P loss of alfalfa and ryegrass grassland in Southwest China was higher than that in other regions. The N and P loss of oat grass grassland in Western China was higher than that in other regions. (4) In 2014, the N and P accumulation of cultivated grassland were positive except for N accumulation in ryegrass grassland. The accumulation rate of alfalfa grassland in Western China was higher than that in Eastern China. There was no regular regional change of N and P accumulation for ryegrass grassland. The N and P accumulation rate of oat grass grassland in Tibet Plateau was higher than that in other regions. 【Conclusion】In 2014, there was a large gap of N and P input (output) for alfalfa, ryegrass and oat grass grassland in different regions of China. N fixation was the major way for alfalfa to acquire N nutrition, so alfalfa grassland management should reduce the input of N fertilizer. Oat grass and ryegrass mainly get the required nutrients by chemical fertilizer, so it should pay attention to fertilizer application for oat grass and ryegrass grassland. The NUE of target forage species was higher than 60%, but PUE was relatively low. Ryegrass grassland was deficient in N, and it is necessary to apply more nitrogen fertilizer. other cultivated grasslands had surplus of N and P in varying degrees, so the excessive application of fertilizer should be controlled.