The integrated effect of milk vetch (Astragalus sinicus L.) and rice straws combined with nitrogen reduction on dry matter, nitrogen uptake, and transport during key growth period in rice, and rice yield was studied to provide the theoretical basis for green and efficient cultivation in rice. A field experiment was conducted at Hantang Experimental Base of Hanzhong Institute of Agricultural Sciences, Shaanxi Province from 2019 to 2021. The randomized block design was adopted and repeated for 3 times. The tested rice variety was high-quality indica rice ‘Huanghuazhan’. Five treatments included: (1) winter fallow, no rice straw mulching, no fertilization (CK); (2) winter fallow, no rice straw mulching, conventional nitrogen fertilizer rate (NPK); (3) planting green manure in winter, rice straw mulching with conventional nitrogen fertilizer rate (GRN100); (4) planting green manure in winter, rice straw mulching with 80% conventional nitrogen fertilizer rate (GRN80); (5) planting green manure in winter, rice straw mulching with 70% conventional nitrogen fertilizer rate (GRN70). The dry matter accumulation, nitrogen accumulation, nitrogen transport and nitrogen utilization at the full heading and mature stage in rice were analyzed. The results showed that: (I) Compared with NPK, the yield of rice increased by 3.50%-7.65% under the milk vetch+rice straw treatments, and the dry weight of stem sheath, leaf, and panicle increased by 25.54%-44.79%, 44.79%-53.74%, 33.76%-61.81% at the full heading stage. The dry weight of stem sheath and leaf increased by 6.87%-25.57%, 20.87%-23.46% at maturity stage. Compared with GRN100, the grain yield of GRN80 and GRN70 was increased by 4.00%-2.77%, the dry weight of panicle increased by 21.33%-4.56% at the full heading stage, and the dry weight of stems sheath, and panicle increased by 17.52%-10.91% during the mature stage of GRN80. (II) Compared with NPK, the nitrogen accumulation in stem sheath, leaf and panicle of the milk vetch+rice straw treatments increased by 34.84%-60.59%, 50.41%-69.28%, 26.57%-45.35% during the full heading stage, 48.61%-54.78%, 54.67%-91.81%, 6.42%-19.96% at mature stage, 16.89%-64.99% in stem sheath nitrogen transport, 47.85%-73.05% in leaf nitrogen transport, and 27.75%-41.09% in nitrogen transport contribution rate. Compared with GRN100, nitrogen increasement in the panicle of GRN80 increased by 19.76%, and nitrogen transport capacity, stem sheath transport rate, leaf transport rate, and nitrogen transport efficiency increased by 7.46%, 2.73%, 9.35%, and 6.86%, respectively. (Ⅲ) Compared with NPK, the nitrogen dry matter production efficiency decreased by 10.64%-20.92%, the nitrogen fertilizer physiological utilization efficiency decreased by 17.88%-32.89%, the nitrogen fertilizer agronomic efficiency increased by 7.81%-63.03%, the nitrogen recovery rate increased by 57.36%-97.19%, and the nitrogen fertilizer partial productivity increased by 3.55%-52.00%. Compared with GRN100, GRN80 and GRN70 increased nitrogen dry matter production efficiency by 13.00%-10.97%, nitrogen fertilizer physiological utilization efficiency by 12.34%-22.37%, nitrogen fertilizer agricultural efficiency by 35.66%-51.21%, nitrogen recovery rate by 21.04%-25.52%, and nitrogen fertilizer partial productivity by 30.04%-46.79%. In conclusion, the co-incorporation of Chinese milk vetch and rice straw in winter accompanied by reducing 20% or 30% N application rate based on conventional N application rate, can significantly increase rice yield, nitrogen absorption and transportation and nitrogen utilization. It may be a green and efficient cultivation model suitable for rice production in the Hanzhong region.
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