核桃—紫花苜蓿复合栽培的根系分布及生长动态

Root Distribution and Growing of Walnut Trees and Medicago sativa Sod-culture Pattern

通过小区试验,研究了核桃林下紫花苜蓿地上生物量、根系分布情况以及核桃的侧根分布情况、灌水1个月后光响应曲线、最大净光合速率和土壤水分状况。研究结果表明:通过3次收割,紫花苜蓿一年产量为90.25 kg·hm-2,且随时间推移,每次收割产量呈下降趋势。从光响应来看,苜蓿最大净光合速率为12.3μmol·m-2·s-1,光饱和点为950μmol·m-2·s-1,核桃树遮阴对其生长有一定的影响。从核桃根系和苜蓿根系的分布情况来看,紫花苜蓿主要分布在土壤20 cm以上浅层,而核桃的侧根在20 cm土层中占到总侧根重量的4.8%,核桃根系与紫花苜蓿根系对水、肥发生一定的竞争,但竞争相对比较小。紫花苜蓿有效地利用了上层土壤水分,减少了裸地土壤的蒸发,使水分得以充分有效的利用。

The ecological orchard cultivation mode, with herbaceous plant as soil cover under fruit trees or in the whole orchard, is one of the main cultivation techniques of green fruit. Sod covering the ground could alleviate the wind erosion greatly in winter, reduce soil, fertilizer and water loss in rainy season of midsummer, and is very helpful to improve the ecology and environment. Other studies have shown that the orchard grass could impact tree shape, change the leaf nutrition, and increase fruit yield and quality. Field experiments were conducted to investigate the suitable sod culture pattern of walnut trees followed by alfalfa （Medicago sativa） intercropping. We measured the aboveground biomass, maximum net photosynthesis rate,light response curve one month after irrigation, roots system distribution of M. sativa, lateral roots distribution of walnut trees and soil water content. Our results showed that, after three times of harvestry,each acre yield per year of alfalfa could reach 1 353.7 kg,and yield of each harvestry decreased with the time elapsed. The maximum net photosynthesis rate peaked at 12.3 μmol · m^-2 . s^-l,light sat- uration point was 950 μmol · m^-2 · s^-1 ,and the shading of walnut affected the growth of alfalfa. The alfalfa roots mainly distributed at the shallow layer （ 〉 20 cm soil depth） , whereas in this soil layer lateral roots of walnut trees occupied only 4.8 % of its total biomass, indicating a certain competition between alfalfa and walnut trees for soil water and nutrition. Alfalfa could effectively use the shallow soil water to reduce the water evaporation of bare field, and elevated the water using efficiency. The above research result has important practical significance to strengthen the management of orchard g rass planting.