Spectral characteristics of summer maize and the responses of its grain yield to nitrogen and phosphorus fertilization under drip irrigation

Abstract

【Background and Objective】 Excessive application of nitrogen and phosphorus fertilizers not only results in environmental pollution but also leads to excessive crop growth, thereby compromising ultimate crop yields. This paper investigates the feasibility of using hyperspectral technology to phenotype crop canopy and crop growth and to improve nitrogen and phosphorus fertilizations. 【Method】 The experiment was conducted from 2022 to 2023 in a maize field. In 2022, nitrogen fertilizations were 0, 120 kg/hm2 and 240 kg/hm2 of nitrogen, and phosphorus fertilization was 0 and 100 kg/hm2 of P2O5. In 2023, the nitrogen applications remained unchanged, but the phosphorus fertilizations changed to 0, 60 kg/hm2 and 120 kg/hm2. All treatments were irrigated by drip irrigation. In the experiment, spectral characteristics of the canopy, dry matter accumulation and grain yield were measured regularly to analyze their response to nitrogen and phosphorus applications. 【Result】 ① The spectral reflectance of the summer maize increased significantly with N and P applications. Compared with the treatments without N and P fertilizations, N fertilization increased the spectral reflectance by 9.61%-18.60% and 3.06%-7.06%, respectively. ② The quality of dry matter and grain yield both increased with the increase in N and P fertilization. The combination of N and P fertilization significantly increased above - ground biomass and grain yield. Compared to control without fertilization, N and P fertilization increased the grain yield by 8.82%-24.27%, while compared to those with only P fertilization, it increased the grain yield by 15.75%-65.79%. N-P coupling had a significant effect on both quality of dry matter quality and grain yield (P<0.01). ③ Both the normalized index and the difference index were correlated with the quality of dry matter, especially at the jointing stage, the heading stage and the filling stage, where their correlation coefficients reached as high as 0.93. 【Conclusion】 The wave bands DVI (810,680), MCARI1 and DVI (761,383) can be used to estimate the vegetation index at jointing stage, heading stage, and filling stage, respectively. From the two-year experiment, the N fertilization of 240 kg/hm2 combined with P2O5 fertilization of 100 kg/hm2 significantly improved the dry matter quality, the number of grains per ear and 100-grain weight, thereby increasing gain yield, compared to other treatments.

Keywords

• nitrogen and phosphorus regulation under drip irrigation
• summer maize
• canopy spectral reflectance
• above-ground dry matter mass
• yield