Comparison of productivity between tropical and temperate maize, 2: Parameters determining the productivity in relation to the amount of nitrogen absorbed.
1995
Osaki M.
Effect of the nitrogen application rate on the productivity of tropical and temperate maize was examined by parameter analysis as follows. 1) Biological yield (Yb) was higher in temperate maize than in tropical maize. Yb was parametrized as: Yb = NAR x LAD and +Yb = Eu x Ea, where NAR is the net assimilation rate, LAD is the leaf area duration, Eu is the solar energy use efficiency, and Ea is the amount of solar energy absorbed in canopy. Yb of tropical maize was determined by LAD, not by NAR which was however very high in tropical maize. Eu was lower in tropical maize than in temperate maize, while Ea was not appreciably lower in tropical maize than in temperate maize, indicating that Eu, not Ea is important to determine Yb. 2) The economic yield (Ye) was parametrized as: Ye = Yb x HIdm, Ye = Yb(Nh) x HIn/Nc(h.o.) x 100, and Ye = Gn x Gw/1,000, where HIdm and IHn are the harvest index of dry matter and nitrogen, respectively, Yb(Nh) is the amount of nitrogen accumulated in plant at harvest, Nc(h.o.) is the nitrogen content in harvesting organs (grains), Gn is the grain number, and Gw is the 1,000 grains weight. In tropical maize in the lowlands in the summer season, HIdm and HIn wee low, and (Nc(h.o..) was high compared to temperate maize. Therefore, even if tropical maize can absorb a sufficient amount of nitrogen, Ye of tropical maize is lower than that of temperate maize. 3) Relationship between the amount of dry matter (DM) and amount of nitrogen absorbed (Nt) at a given time was expressed as: DM=DMo x exp(CNI x Nt), where DMo is the initial value of DM and CNI is the carbon-nitrogen index. Further more CNI was correlated with Nt at harvest (Nh) as: 1/CNI=a x Nh + b, where a and b are coefficients. The coefficients a and b in tropical maize were very similar regardless of the difference in varieties and growth conditions. In tropical maize, the coefficient a was high and coefficient b was low when compared to temperate maize.
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