Effects of Reduced Nitrogen Fertilization Via Controlled Release on Dry Matter Accumulation, Photosynthetic Traits and Yield of Proso Millet

Abstract

【Objective】 Proso millet is a common crop cultivated in the Loess Plateau in northwestern China and sustainable production needs to reduce nitrogen fertilization. This paper presents the findings of an experimental study that investigated the impact of reducing nitrogen fertilization through controlled release on photosynthetic traits and yield of the millet. 【Method】 The field experiment was conducted with application of 120 kg/hm2 of urea taken as the control (TN). There were seven controlled-release treatments, which applied N fertilizer at 120 kg/hm2 (T1), 108 kg/hm2 (T2), 96 kg/hm2 (T3), 84 kg/hm2 (T4), 72 kg/hm2 (T5), and zero (T0). During the experiment, we measured the changes in dry matter accumulation, photosynthetic traits of the flag leaves, SPAD, NBI and yield of the millets in each treatment and the CK. 【Result】 ①Nitrogen fertilization significantly improved the dry matter accumulation and photosynthetic traits of the flag leaves at all growing stages, regardless of treatments. Compared with CK, applying the same amount of N fertilizer but at controlled release increased the dry matter accumulation in the middle and late stages by 4.44%~8.77%, proportion of the dry matter allocated to the ears at maturity stage by 1.58%~2.75%. ②Depending on the application rate, controlled release of N fertilizer led to a 2.19% to 5.05% increase in chlorophyll content and a 2.66% to 8.34% increase in nitrogen balance index of the flag leaves; it also increased the net photosynthetic rate, stomatal conductance and transpiration rate at the filling stage by 3.90%, 6.40% and 4.20%, respectively, while reducing the average intercellular CO2 concentration by 4.45%. ③With the decrease in controlled-release N fertilization, both dry matter accumulation and photosynthetic rate decreased, and the decrease was more significant in T3—T0. SPAD and NBI of the flag leaves were positively correlated with the dry matter accumulation, net photosynthetic rate and the yield; the correlations between yield and NBI at the jointing and filling stages was significantly positive. ④Applying the same amount of N as in TN but with controlled release increased the yield of the millet by 4.42%, equivalent to an increase in net income by 121~280 Yuan/hm2. Reducing 10%~20% of N used in the TN with the controlled release did not reduce the yield significantly, but further reduction beyond 20% led to a decrease in yield by 3.19%~5.23%. 【Conclusion】 Applying N fertilizer in controlled release to proso millet in hilly areas in Loess Plateau can improve its yield. It hence has a potential application for other crops in this region and other regions with similar growing environments.

Keywords

• dry matter accumulation and distribution
• nitrogen balance index
• net photosynthetic rate
• spad