Fertilizer application increases alfalfa yield and crude protein content: roles of fertilizer type, application rate, and environmental conditions

Abstract

Abstract Insufficient supply of high-quality forage is a critical factor constraining the growth of the livestock industry. Cultivated grasslands, such as alfalfa (Medicago sativa L.) grasslands, play a vital role in addressing this issue. Fertilizer application is an effective strategy for enhancing alfalfa yield and forage quality; however, optimizing management practices is essential for adapting to variable environmental conditions. In this study, we conducted a meta-analysis to evaluate the impact of fertilizer application on alfalfa productivity, taking into account fertilizer type, application rate, and environmental factors. Fertilizer application significantly increased overall alfalfa yield and crude protein content by 17.7% and 5.8%, respectively, compared to the no-fertilizer group. Manure application contributed to a greater increase in alfalfa yield than phosphorus (P), potassium (K), and nitrogen (N) fertilizers, with increments of 14.0%, 24.9%, and 25.6%. Considering alfalfa yield, quality, and crude protein content, the optimal application rates for N and P fertilizers were found to be 100–150 kg ha− 1 and 150–200 kg ha− 1, respectively. We also found that N and K fertilizers were more effective under lower (≤ 10℃) mean annual temperatures (MATs), while P fertilizer and manure performed better under higher MATs. N fertilizer and manure led to greater yield increases under higher mean annual precipitations (MAPs), whereas P and K fertilizers demonstrated lower use efficacy under the same conditions. Additionally, the application of N, P, and K fertilizers, and manure resulted in higher crude protein content under lower MATs and MAPs. Although soil conditions influenced growth and production, their effects on the fertilization impact of all fertilizers on alfalfa yield and crude protein content were limited. These findings provide valuable insights for the development of optimized fertilizer management strategies by taking into account site-specific differences, environmental factors, and other management practices. Future research should focus on integrating additional forage quality parameters, exploring the synergistic effects of different fertilizers, and evaluating the long-term sustainability of these practices.