Optimization of nitrogen fertilizer application enhances biocontrol function and net income

Authors: WANG, LEYUN - China Agricultural University; GAO, FENG - China Agricultural University; Reddy, Gadi V.P.; ZHAO, ZIHUA - China Agricultural University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2020
Publication Date: 5/31/2020
Citation: Wang, L., Gao, F., Reddy, G.V., Zhao, Z. 2020. Optimization of nitrogen fertilizer application enhances biocontrol function and net income. Journal of Economic Entomology. https://doi.org/10.1093/jee/toaa112.
DOI: https://doi.org/10.1093/jee/toaa112

Interpretive Summary: Low soil nitrogen level, especially in depleted croplands, is a major limitation for the growth of grain crops, and the application of nitrogen fertilizer has been increasingly used to enhance grain yields. High nitrogen input can facilitate the growth of both the crop foliage and the populations of key crop pests. Nitrogen fertilizer also plays an important role in mediating tritrophic interactions in agroecosystems. Understanding how different levels of nitrogen fertilizer affect each trophic level is crucial for evaluating the efficiency of an agroecosystem, managing insect pests and promoting biological control through natural enemies. The field experiments were conducted to study how different levels of nitrogen fertilizer input affect the naturally occurring populations of cereal aphids and their primary parasitism rates in wheat fields. The results indicated that while the increased application of nitrogen fertilizer from medium to high enhanced grain yield non-significantly, and net income decreased significantly with the same change, which suggests that the extra nitrogen input may have mostly gone to the non-grain parts of wheat, their herbivores, and/or have been lost through leaching instead of filling grain.

Technical Abstract: The intensive use of nitrogen fertilizer has been a common approach for pursuing higher crop yields. However, the ecological effects of such use on the tritrophic interactions (crop-insect pest-natural enemy) and on the ecological and economic benefits of such use are poorly understood. Here, we investigated the effects of low, medium, and high levels of nitrogen fertilizer inputs (70, 140, and 280 kg/ha/year) on cereal aphid (Sitobion avenae Fabricius, Schizaphis graminum Rondani, and Rhopalosiphum padi L.) abundance, primary parasitism rates, crop yield, and net income in winter wheat (Triticum aestivum cv. Zhou 22) for two years. A higher input of nitrogen fertilizer significantly enhanced the abundance of cereal aphids, while their primary parasitism rates (26.9 ± 3.5% in 2018 and 24.9 ± 4.5% in 2019) were highest at the medium nitrogen level. The performance of participants in the wheat-aphids-parasitoids system was likewise mediated by the nitrogen fertilizers. Meanwhile, wheat yield significantly increased with moderate increases in the nitrogen level, although overuse of nitrogen fertilizer did not significantly further enhance wheat yield. Finally, we found either low or overuse of nitrogen fertilizers resulted in lower net income than did medium nitrogen fertilization. These results demonstrate the need to re-evaluate and adjust fertilizer use to optimize the eco-economic and sustainable management of agroecosystems.