Abstract: The yield of oat in rainfed farmlands is low and unstable. Here, we investigated the coupling effects of water-retaining agent and microbial fertilizer, which have been widely used in dry farming systems. There were four treatments: single application of water-retaining agent (A), single application of microbial fertilizer (B), combination of waterretaining agent and microbial fertilizer (AB), control (CK). The effects of amendments on dry matter accumulation, allocation, transportation, and water use efficiency of oat in different growth stages were evaluated, aiming to find the effective strategy in improving oat yield in rainfed farmland. The results showed that both single and combined water-retaining agent and microbial fertilizer application affected the accumulation and allocation of dry matter in different organs of oats in different growth stages, and promoted transformation of dry matter from leaves to stems in the early growth stage, and from stems and leaves to spikes and grains in late stage. Allocation ratios in the AB treatment significantly differed compared to that in CK in the whole growing stage. Compared to treatments A, B and CK, AB increased stem allocation ratio by 13.13%-28.61% in jointing stage, ear allocation ratio in flowering and filling stage by 21.46%-36.45%, and gain allocation ratio by 0.26%-3.94% in mature stage. The AB treatment showed a relatively higher amount of dry matter accumulation and water use efficiency in all stages, with a significant difference in sowing stage to jointing stage and filling stage to mature stage, compared to CK. In these two stages, dry matter accumulation amount increased by 41.98%-55.14% and 2.64%-90.92%, and water use efficiency increased by 40.92%-71.04% and 4.96%-96.35%, respectively. Both single and combined water-retaining agent and microbial fertilizer application facilitated dry matter accumulation after anthesis and its contribution to grain yield, and thus improved oat yield in rainfed farmland. The effects of combination treatment were better than the two single application treatments, with an increase of 8.38%-22.92% for dry matter accumulation after anthesis, 0.18%-2.26% for contribution rate after anthesis, and 8.40%-20.12% for grain yield.

Key words: oat, water-retaining agent, microbial fertilizer, dry matter, yield.