Preliminary Construction of a Diagnostic Model for Nitrogen Nutrition Based on SPAD Values in Leaves of Hybrid Rice
A split experiment of two-factor was conducted to explore the best measured leaf position of the SPAD value of rice leaves,the best secondary index of SPAD value,and build a nitrogen(N)nutrition diagnosis model based on the SPAD value of rice leaves.The main plots consisted of variety treatment(two variety:Qyou 6 and Yixiangyou 2115)and the subplots consisted of the N application rate(five N levels:0,75,150,225,300 kg/hm2).The sensitivity,representativeness,and stability of rice leaves were analyzed.The relationship between SPAD value index and N application rate and leaf N content(LNC),and the relationship between leaf N accumulation(LNA)and LNC and yield were studied.The results showed that the sensitivity,representativeness and stability of rice leaf in order of magnitude were L4＞L3＞L1＞L2,L3＞L4＞L2＞L1,L2＞L3＞L4＞L1,respectively.Thus,L3 and L4 can be used as the common ideal indicator leaves for N nutrition diagnosis.The geometric mean of SPAD value of the top 3 and 4 leaves of rice plant(GMSI34)was selected as the best secondary index of SPAD value.According to the parabola equation of LNA and yield,univariate linear regression equation of LNA and LNC,and the exponential equation of GMSI34 and LNC,the critical values of SPAD value secondary index(GMSI34cri)at jointing stage,booting stage,and heading stage are 48.5,44.3,and 42.9,respectively.Compared with the actual GMSI34(GMSI34act),if GMSI34act＜GMSI34cri,it indicates that rice lacks nitrogen and needs nitrogen topdressing,if GMSI34act≥GMSI34cri,it shows that the rice has sufficient nitrogen nutrition and does not need nitrogen topdressing.In conclusion,the N nutrition diagnosis model based on the SPAD value of hybrid rice leaves can provide technical support for efficient N fertilizer management of hybrid rice.
hybrid riceleaf positionSPAD valuenutrition diagnosis model
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