What question did this study set out to answer?

The central aim is to evaluate how alfalfa incorporation and nitrogen application affect carbon and nitrogen metabolism and productivity in smooth bromegrass.

February 8, 20260 citationsOpen Access

Enhancing Carbon–Nitrogen Metabolism and Productivity of Smooth Bromegrass Through Alfalfa Incorporation and Nitrogen Application

FHFeng HaoJilin University JYJiabing Yu TYTiefeng YuUniversity of California, Berkeley

Key Points

The central aim is to evaluate how alfalfa incorporation and nitrogen application affect carbon and nitrogen metabolism and productivity in smooth bromegrass.
Conducted over two consecutive years with various nitrogen application rates and alfalfa incorporation levels.
Analyzed physiological and biochemical parameters including net photosynthetic rate, transpiration rate, and enzyme activities.
Evaluated productivity through a multi-objective model using entropy-weighted TOPSIS.
Transpiration rate increased by 43.64%, intercellular CO2 concentration by 40%, and stomatal conductance by 48.09% under optimal conditions.
Peak photosynthetic rate increased by 65.63% with higher nitrogen application regardless of alfalfa inclusion.
Significant increase in enzyme activities: nitrate reductase by 154.60%, glutamine synthetase by 112.39%, and RuBisCO by 199.19%.
Total sugar and protein production increased by 122.22% and 145.17%, respectively.
Optimal forage productivity was achieved with 20% alfalfa incorporation and 105 kg N·ha−1 application.

Abstract

The incorporation of alfalfa into grass systems reduces reliance on nitrogen fertilizer application. Over two consecutive years, we investigated the regulation of carbon and nitrogen metabolism in grasses and productivity enhancement under four nitrogen application rates (0, 105, 210, and 315 kg·ha−1) and five alfalfa incorporation levels (0%, 10%, 20%, 30%, and 40%); incorporation (%) refers strictly to seeding proportion (% of the monoculture seeding rate). Within the range of 20–30% alfalfa incorporation and 105–210 kg·ha−1 nitrogen application, key physiological and biochemical parameters, except the net photosynthetic rate (Pn), reached their peak values compared to the N0A0 (no nitrogen and no alfalfa) treatment. Transpiration rate (Tr), intercellular CO2 concentration (Ci), and stomatal conductance (Gs) increased by 43.64%, 40%, and 48.09%, respectively. Pn peaked under the N2A0 treatment (210 kg·ha−1 nitrogen application and no alfalfa), increased by 65.63%. Nitrate reductase (NR), glutamine synthetase (GS), and ribulose-1,5-bisphosphate carboxylase (RuBisCO) activity increased by 154.60%, 112.39%, and 199.19%, respectively. Total sugar (TS) and protein production (YCP) increased by 122.22% and 145.17%, respectively. The entropy-weighted TOPSIS evaluation based on multi-objective assessment showed that the combination of 20% alfalfa incorporation with 105 kg N·ha−1 application is an efficient model for enhancing forage productivity in the Horqin Sandy Land.

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