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In order to explore the effects of water-nitrogen coupling on dry matter and nutrient accumulation of flue-cured tobacco, 9 treatments with different lowest limits and nitrogen fertilizer amount were designed, and the distribution and accumulation of dry matter and nutrient (N, P and K) of flue-cured tobaccos under water-nitrogen coupling treatments were observed. Results showed that: (1) High irrigation amount could not certainly increase the dry matter accumulation of tobacco root, but which was beneficial to the dry matter accumulation of whole tobacco plant. (2) Dry weight proportion of flue-cured tobacco leaves was highest, which was above 55% among the treatments. (3) Higher water and nitrogen promoted the nutrient accumulation of flue-cured tobaccos, nutrient content of W3N3, W3N2 and W2N2 was higher compared to other treatments.

A pot experiment was conducted on soil evaporation of flue-cured tobaccounder water and nitrogen fertilizers coupling treatmentsin this study. Soil evaporation at each growth stage of tobacco were analyzed, so did ratio of average soil evaporation (AEa) to mean water consumption (AET). Some factors impacting soil evaporation were also investigated. The results showed that average daily soil evaporation was positively correlated with soil temperature (p), the equation between daily soil evaporation and surface soil moisture (θ) was AEa=0.058e0.048θ (R2=0.717), while relationship between the ratio of evaporation to water consumption (AEa/AET) and leaf area index (LAI ) was functioned as AEa/AET=0.201 LAI-0.912(R2=0.658). It also suggested that the best effects to decrease soil evaporation of flue-cured tobacco appeared in treatment of 6g N per plant combined with the irrigation amount and frequency at 4.5kg and 9 times, 18kg and 18 times, 13kg and 26 times at root spreading stage, vigorous growing stage and the maturing stage respectively.

Field experiments were conducted for controlled and mid-gathering irrigation mode in Nanjing, Jiangsu Province, focusing on the effect analysis of this mode with different fertilizations on profile soil total nitrogen and alkali-hydrolyzale nitrogen distributions and rice yield compared with the conventional irrigation mode. Results obtained showed that both total nitrogen and alkali-hydrolyzale nitrogen in soil profile were decreased with the increase of soil depth. Fast decrement of total nitrogen was found from surface 0-20 cm of soil layer and it reached the plateau below 40 cm of soil layer. Under the same fertilizer application, both total nitrogen and alkali-hydrolyzale nitrogen in surface soil layer were lower under controlled and mid-gathering irrigation mode which reduced the loss risks of runoff and leaching of soil and fertilizer nitrogen. Controlled and mid-gathering irrigation reduced water comsumption and N pollutant discharge without significant changes in rice yield compared with conventional irrigation. Conjunction of organic and inorganic fertilizers significantly improved the rice yield and utilization rate of nitrogen.

Nitrogen utilization efficiency (NUE) was a hot topic in the study area of crop cultivation, most scholars tented to calculate NUE by D-value method, which could well reflected the total absorption of N nutrient by crops; and on the other hand, the tracing technique could precisely calculated the N content which crops absorbed from N fertilizer. In this study, the flue-cured tobaccos were treated with 2 N levels and 3 water levels, and the D-value method and the tracing method was adopted to calculate the nitrogen utilization efficiency. Results showed that the RD value was more than double the RN value, and there were no relationships between the results calculated by the D-value method and the tracing method, the treatment with higher RN value could not always obtain a higher RD value; besides, water deficiency or excess could both decreased NUE, through affecting the N availability or through the elution of the N nutrient. Taken as the whole, 6g/plant N combined with 800mm irrigation water was more beneficial for the effective utilization of N fertilization, and which combined with 1000mm was more beneficial for the N accumulation of tobacco plants.

Based on field experiment, the yield and water use efficiency (WUE) of tobacco under different nitrogen levels were studied in Hunan province, China. The results show that the evaportranspiration (ET) of flue-cured tobacco dealt with N2 (90kg N fertilizers per ha) gets to the maximum. In addition, the vigorous period has the maximum ET due to the critical period of water requirement. The linear relationship is established among fertilization, yield and water use efficiency. Reasonable fertilizer application can increase water use efficiency and flue-cured tobacco yield.

Raising nitrogen utilization efficiency could not only cut the fertilizer costs, but also reduce the N loss and residual, which benefits a lot to agricultural production and environmental protection. In this experiment, the 15N tracing technique was employed in order to clear the accumulation and whereabouts of fertilizer N in flue-cured tobacco plants, besides, the tobaccos were treated by six different water-nitrogen modes, for the sake of finding out the best design with the highest nitrogen utilization efficiency. The results showed that more N application contributed to more fertilizer N accumulation, also increased the content of total N; Excess irrigation restrained the tobacco plants' absorption of fertilizer N, ultimately leading to the low utilization efficiency of nitrogen fertilizer; After apex pruning, the N offering ability of the soil was much stronger than that of nitrogen fertilizer, and the fertilizer N accounts a relatively small part for the total N in tobacco plants, the highest nitrogen utilization efficiency was 24.16%, recorded in the design of 800mm irrigation amount and 6g/plant pure N application(T2), Meanwhile, the agronomic characters and crop yield was observed, tobaccos in T2 design performed better than the average level of field-cultivated tobaccos, the conclusions could be obtained that T2 design was preferable, which achieved the highest nitrogen utilization efficiency when ensured the normal growth and good harvest of flue-cured tobacco.