Crop nitrogen monitoring techniques, particularly choosing sensitive monitoring bands and suitable monitoring models, have great significance both in theory and in practice for achieving non-destructive monitoring of nitrogen concentration and accurate management of water and fertilizer in large-scale areas. In this study, a lysimeter experiment was carried out to examine the characteristics of canopy spectral reflectance variation of summer corn under different fertilization levels. The relationship between canopy spectral reflectance and nitrogen concentration was investigated, based on which sensitive bands for the corn canopy nitrogen monitoring were selected and a suitable spectral index model was determined. The results suggest that under different fertilization levels, the canopy spectral reflectance of summer corn decreases with the increase of the canopy nitrogen concentration in the visible light band, but varies in the opposite direction in the near-infrared band, with a premium put on a higher correlation between the spectral reflectance of the characteristic bands and their first derivatives and the canopy nitrogen concentration. The most sensitive bands for monitoring the canopy nitrogen concentration using spectral reflectance and its first derivative are found to be 762 nm and 726 nm and the correlation coefficients are 0.550 and 0.795, respectively. The optimal band combination, generated by multivariate stepwise regression analysis, is composed of 762 nm, 944 nm and 957 nm bands. From the 55 reported spectral index models of crop nitrogen concentration monitoring, the most suitable index model, NDRE, is chosen such that this index model has the highest correlation with the canopy nitrogen concentration in summer corn. This model has a significant positive correlation with the canopy nitrogen concentration at each growth period, and the correlation coefficient is up to 0.738 during the whole growth period. Spectral monitoring models of canopy nitrogen concentration are constructed using sensitive bands, and a combination of bands and the spectral index, suggesting that these models perform well in monitoring. The models arranged in descending order of simulation accuracy are as follows: the suitable spectral index model, the optimal band combination model, the sensitive band reflectance first derivative model, the sensitive band reflectance model. The determination coefficients are 0.754, 0.711, 0.639 and 0.306, respectively.

Based on the location of meteorological stations in Jilin Province, seven meteorological stations were selected. They are Fuyu, Yanji, Linjiang, Ji'an, Meihekou, Tongyu and Changchun. These meteorological data are from the year of 1984 to 2012. The meteorological data are analyzed by using crop coefficient method and water balance principle. The irrigation water requirement during the growth period of Maize in Jilin province was analyzed. The results show that: the average irrigation water requirement is 166mm in the middle of the dry year (75%) and in the drought year (90%).The variation range of irrigation water demand in each weather station is from 0 mm to 375mm. Regional differences are obvious. There is no obvious difference in irrigation water requirement in time. The variation characteristics of irrigation water demand of maize are increasing from east to west.

The effects of different nitrogen application levels on growth, dry matter accumulation, SPAD value, leaf area index and yield of maize were studied to provide theoretical basis for rational and efficient nitrogen application management of crops. In the field experiment, 225, 337.5, 450, and 675 kg ·hm⁻² nitrogen application levels were set, respectively expressed by N₁, N₂, N₃, and N₄. N₀without nitrogen fertilizer was used for the control experiment. During the growing period, plant height, leaf area index and SPAD were observed, and dry matter accumulation, yield and yield components were counted. The growth index, dry matter accumulation, yield and yield components of maize were influenced by different fertilization levels. When the nitrogen application amount is greater than 225 kg · hm⁻², it could significantly promote the growth and development of corn and increase the yield. Through comparative analysis, it was concluded that when the nitrogen application amount was 280kg·hm⁻², it was the optimal nitrogen application amount for the efficient production of corn in the experimental area.