In order to investigate the suitable nitrogen application rate in maize growth process, the Canadian maize variety Pioneer 38B84 was used as the experimental material. Under the condition of nitrogen application at 45 kg hm-2 and basic seedling 79 000 hm-2, 34, 68, 101, 135, 169 and 203 kg hm-2 and nitrogen saturation reference plot on the SPAD value, Dualex value, aboveground biomass and yield of maize spikelets. The results showed that the SPAD value, aboveground biomass and yield increased with the increase of nitrogen requirement, and the Dualex value decreased with the increase of nitrogen requirement. The SPAD-NSI saturation index (SPAD-NSI) of the treated nitrogen 101,135,169 and 203 kg hm-2 was greater than 0.95 on each measurement date. The Dualex-NSI treated with nitrogen-loaded 101 kg hm-2 was greater than 0.95 at 18 ~ 46 d after silking, and Dualex-NSI treated with nitrogen 135,169 and 203 kg hm-2 was greater than 0.95 at each determination date. SPAD, Dualex, SPAD-NSI and Dulaex-NSI were significantly correlated with topdressing nitrogen. At the jointing stage, 101 kg hm-2 or 135 kg hm-2 could meet the requirement of nitrogen growth and obtain the maximum economic yield. The increase in the amount of nitrogen fertilizer had no significant effect on SPAD, Dualex, aboveground biomass and yield when the maximum yield was exceeded. Top dressing not only achieves the same yield effect as the nitrogen saturated reference cell, but also reduces the amount of nitrogen fertilizer applied and reduces the economic input of the grower. Under the experimental conditions, the nitrogen application rate was 101 kg hm-2 or 135 kg hm-2 at the jointing stage. SPAD chlorophyll meter and Dualex instrument can be used to diagnose the nitrogen nutrition status of maize.

HANDHELD NDVI MEASURING INSTRUMENT

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CM-1000 chlorophyll meter is used to accurately measure the relative chlorophyll content of plants and crops. It can improve the management of nitrogen fertilizer application, understand the real nitro demand of plants, and help you understand the lack of nitro in soil or whether excessive nitrogen fertilizer is applied. You can use this instrument to increase the utilization rate of nitrogen fertilizer and protect the environment (prevent the environment, especially the water source, from being polluted by applying too much nitrogen fertilizer).