Construction and Application Effect of the Leaf Value Model Based on SPAD Value in Rice
[Objective]The relationship of different plots, nitrogen application amount, SPAD value derivative index and yield was studied to construct linear model of nitrogen rate based on SPAD value in rice, so as to easily, quickly, perfectly recommend nitrogen rate.[Method]The experiment was conducted by using Qyou6 as the materials with four nitrogen levels (0, 75, 150, 225 kg·hm-2) in 2015 and 2016. We compared the relationship between yield and apparent nitrogen supply of field, and between SPAD value derivative index and apparent nitrogen supply of field in this experiment. And the effect of variable nitrogen application based on leaf value model was also studied.[Result]The results showed that, curve relationship between yield and apparent nitrogen supply of field at heading stage was extremely significant positive correlation, and R2of two years was 0.5523, 0.7148, respectively. In this fitting relationship, the higher yield of every years was 9 264.93 kg·hm-2, 11 167.97 kg·hm-2. The difference of maximum yield was 1 903.14 kg·hm-2in two years, and yield in 2016 was 20.54% higher than that in 2015. But the apparent total nitrogen uptake of the highest yield in different years were close, which was 575.27 kg·hm-2, 546.71 kg·hm-2, respectively. And the difference of apparent total nitrogen uptake was only 28.56 kg·hm-2, and apparent total nitrogen uptake was -4.96% higher than in 2015. The linear relationships between SPADL3(SPAD value of third leaf), SPADL4(SPAD value of fourth leaf), SPADmean(average SPAD value of four leaves), SPADL3×L4/mean(product of SPAD value of third leaf and SPAD value of fourth leaf divided by average SPAD value of four leaves) and apparent nitrogen supply of field were significant or extremely significant under different growth period and year. On single leaf, the change of slope of linear relationship between SPADL3and apparent nitrogen supply was smaller at jointing stage in years, and value of slope was 0.0156 in 2015, 0.0154 in 2016, respectively. At heading stage, the slope of linear relationship between SPADL1and apparent nitrogen supply in 2015 and 2016 was 0.0172, 0.0173, respectively. At joining and heading stage of different years, the slope and origin of linear relationship between SPADL3×L4/meanand apparent nitrogen supply of 2016 increased by-28.70%, 17.41%; -15.34%, 56.11% than that of 2015, respectively. Constructing a new rice nitrogen model based on SPAD value, which was called the leaf value model. The total nitrogen rate of leaf value model was difference between apparent total nitrogen uptake and apparent nitrogen supply of soil, and it could estimate apparent nitrogen supply of soil by measured value of SPAD value derivative index. And R2of linear fitting between SPAD value derivative index and apparent nitrogen supply of field at heading stage was higher than that at jointing stage. At joining stage, the total nitrogen rate which was estimated by SPADL4or SPADL3×L4/meanwas close with that was estimated by SPADL3or SPADmean, and the former was 50% higher than the later. The effect of variable nitrogen application based on leaf value model showed that yield of variable area was 820.68 kg·hm-2higher than that of control area, and nitrogen partial productivity and nitrogen agronomic efficiency of variable area was 13.74%, 103.45% higher than that of control area, respectively. A general expression for leaf value model was Nw=Nz-[(Ys-b)/k-Ng], where Nw, Nz, Ys, Ng meant total nitrogen application rate (kg·hm-2), apparent total nitrogen uptake (kg·hm-2), SPAD value derivative index, base-tiller fertilizer amount (kg·hm-2), respectively, and k, b was slope and origin of linear relationship betweent apparent nitrogen supply of field (Nx) and SPAD value derivative index (Ys), and Nx was sum of nitrogen content of soil (kg·hm-2) and already manure amount. [Conclusion]Variable nitrogen application based on leaf value model could reduce yield difference and increase yield, nitrogen agronomic efficiency, nitrogen partial productivity and nitrogen contribution rate.
riceyieldSPAD value derivative indexapparent nitrogen supply of fieldleaf value modelvariable nitrogen
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