Effects of cultivar and growing degree day accumulations on forage partitioning and nutritive value of common vetch (Vicia sativa L.) on the Tibetan plateau.

BACKGROUND: The use of common vetch in grassland-livestock systems has expanded greatly within recent years, partly because of its value as a high-quality forage crop but also to improve the soil nitrogen availability. In-field estimation of forage yield potential and nutritional characteristics is required for providing management decision to farmers on how to optimize the management and use of common vetch forages. The aim of this work was to study changes in forage partitioning and nutritive value responses of a late-maturing and an early maturing cultivar of common vetch in a two-year study on the Tibetan Plateau. RESULTS: This study provided evidence for differential patterns of forage accumulation for common vetch with contrasting maturity over 2 years. The late-maturing cultivar exhibited greater forage yield and a lower proportion of pods, compared to the early maturing cultivar. There was a tendency towards lower forage nutritive value with the late-maturing cultivar. Regressions of nutritive value parameters of common vetch forages on growing degree days were explained by the cubic (P < 0.001) models, all with high coefficients of determination (R2 ≥ 0.792). CONCLUSION: This study shows that the late-maturing cultivar harvested at end of the pod-filling stage produces high forage yield, increasing the availability of high-quality forage for ruminants, thereby improving the self-sufficiency of farmers, in terms of forage yield and high-concentration protein. For early maturing cultivars, it may be better to harvest at the early flowering stage for better nutritive value and in part to enable a subsequent double crop of oat. © 2020 Society of Chemical Industry.

Insufficient nitrogen supply from symbiotic fixation reduces seasonal crop growth and nitrogen mobilization to seed in highly productive soybean crops.

Nitrogen (N) supply can limit the yields of soybean [Glycine max (L.) Merr.] in highly productive environments. To explore the physiological mechanisms underlying this limitation, seasonal changes in N dynamics, aboveground dry matter (ADM) accumulation, leaf area index (LAI) and fraction of absorbed radiation (fAPAR) were compared in crops relying only on biological N2 fixation and available soil N (zero-N treatment) versus crops receiving N fertilizer (full-N treatment). Experiments were conducted in seven high-yield environments without water limitation, where crops received optimal management. In the zero-N treatment, biological N2 fixation was not sufficient to meet the N demand of the growing crop from early in the season up to beginning of seed filling. As a result, crop LAI, growth, N accumulation, radiation-use efficiency and fAPAR were consistently higher in the full-N than in the zero-N treatment, leading to improved seed set and yield. Similarly, plants in the full-N treatment had heavier seeds with higher N concentration because of greater N mobilization from vegetative organs to seeds. Future yield gains in high-yield soybean production systems will require an increase in biological N2 fixation, greater supply of N from soil or fertilizer, or alleviation of the trade-off between these two sources of N in order to meet the plant demand.