Effect of Rhizobium inoculation on alfalfa under subsurface drip irrigation

A locally isolated Rhizobium strain (Sinorhizobium meliloti XGL026) labeled with the green fluorescent protein (GFP) gene was used to inoculate alfalfa to quantify competitive nodulation performance and evaluate the effect on yield and quality of alfalfa in the field under subsurface drip irrigation. The results showed that inoculating rhizobia under drip irrigation from the first to third cuts of 4-year-old alfalfa could significantly increase the number and weight of nodules and increase the percentage of nodules (P < 0.05). Compared to controls with only N+P+K and P applications, Rhizobium inoculation treatment increased the average nodule number from the first to third cuts by 16.4 and 21.2 per individual plant, the average nodule weight by 0.029 and 0.033 g, and the average nodulation rate by 49% and 78%, respectively. Rhizobium inoculation could significantly increase the fresh and dry yield from the first to third cuts by 15.8% and 18.9%, respectively, compared with those of the controls. The crude protein content increased by 2.16%, whereas the NDF and ADF decreased by 3.25% and 5.00%, respectively, which indicated that the quality of alfalfa was significantly improved. The effect of applying nitrogen and phosphorus fertilizers and simultaneously inoculating with rhizobia (treatment XGL026+N+P) was better than applying only phosphorus and inoculating with rhizobia (XGL026+P). The results showed that XGL026+N+P had better inoculation effect; it also significantly increased the nodulation capacity, and yield and quality of alfalfa, and reduced the application of chemical fertilizers. This study provides a scientific basis for the application of Rhizobium inoculation to improve the quality and efficiency of alfalfa production under drip irrigation.