Coupling Effect Of Water And Nitrogen On Greenhouse Cucumber With Fertigation

This experiment carried in greenhouse of Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of Ministry of Education in Northwest A&F University from August to November in 2013, and in view of the questions of irrigation and nitrogen unreasonable in the vegetable greenhouse for semiarid northwest area. Choosing ‘Bonai 9-1’ as the test cultivar, the greenhouse plot experiment was subjected to three irrigation water levels [W1(60% ET0), W2(80% ET0) and W3(100% ET0)] in interaction with four nitrogen fertilization levels [N0(0 kg/hm2), N1(180 kg / hm2), N2(360 kg/hm2), N3(540 kg/hm2)], and there were 12 treatments in total. The effect of different water and nitrogen supply on cucumber growth, yield, quality, water and nitrogen use and soil environment were investigated, in order to regulate water and fertilizer scientifically and provide scientific reference for actual production. The results showed that:(1)In addition to stem diameter, irrigation and nitrogen application influenced cucumber plant height, leaf area index, and dry weight significantly. Irrigation had a significant positive correlation effects on plant height and leaf area index, whereas the impact of nitrogen fertilizer on cucumber growth showed different trends due to the different nitrogen levels. The impact of nitrogen fertilizer on Plant height and leaf area index showed an increasing trend and then decreasing, reaching the maximum at N2 treatment. Dry weight was slightly different, which showed under W1 level, reaching the maximum at N2 treatment, decreasing slightly at N3 treatment afterwards, and there were no significant difference at the N2 and N3 treatment. The remaining irrigation levels showed varying degrees of increase with the increasing of nitrogen fertilizer.(2) Irrigation and nitrogen application influenced yield and yield components significantly, cucumber yield increased with the increasing of nitrogen rate. When the nitrogen rate increased to N2 level, and continued to increase, the effect of yield showed different trends under different irrigation levels. In other words, there was no significant difference between yield when nitrogen rate increased to N2 levels and continued to increase under W1 and W2 level, while difference was significant between N2 and N3 treatment and N3 improved yield by 8.4% than N2 under W3 level. Changes of fruit number and average fruit weight were similar to cucumber yield, and the fitting relationship of fruit number and yield, average fruit weight and yield all showed a linear relationship, R2 were 0.989 and 0.934 respectively. Via the path analysis between yield and growth index, it showed that dry weight and leaf area index had the important effects on cucumber yield improvement, which can be used for the first and second index of high yield.(3)Irrigation amount was significantly negatively correlated with cucumber soluble solids, soluble sugar and nitrate contents. Along with the increasing of irrigation levels, Vc content showed an increasing trend and then decreasing, while the soluble protein content showed different trends under different irrigation and nitrogen conditions. Soluble solids and nitrate content in the fruit were significantly increased with increase of nitrogen, but soluble sugar and Vc content showed an increasing trend and then decreasing. According to the comprehensive evaluation of the cucumber quality and nutrition output with principal component analysis, W1N2(60%ET0、360 kg/hm2 N) obtained the best quality, and W2N2(80%ET0、360 kg/hm2 N) gained the maximum nutrition output of cucumber, which can be used as a suitable choice to obtain high yield and quality in agricultural production.(4)Chlorophyll content of cucumber showed an increasing trend and then decreasing with the growth progress, and obtained maximum at full bearing period. In fruit setting stage, full bearing period and telophase of fruiting, appropriate amount of nitrogen had a role in promoting chlorophyll content increasing, whereas excessive nitrogen application restrained chlorophyll synthesis under W1 and W2 levels. However, the coupling effect between water and nitrogen was more conducive to chlorophyll synthesis for the demand for water and nutrients, showing a positive correlation under W3 level. The diurnal variation of Pn of cucumber appeared a single peak curve in the condition of water and nitrogen supply. No nitrogen or severe water deficit would significantly affect Pn, and appropriate amount of water and fertilizer conservation could not only save costs, but also achieved better Pn comparing to full irrigation and fertilizer application.(5)Irrigation and nitrogen fertilization influenced cucumber IWUE and WUE significantly, and water and nitrogen interactions also had a significant effect on WUE, but the interaction of water and nitrogen had no significant effect on IWUE. With different irrigation levels, WUE expressed as W2>W1>W3 under the same N application. Under W1 and W2 treatment, WUE showed an increasing trend and then decreasing with the increase of nitrogen rate, while for W3 treatment, WUE was significantly increased with the increase of nitrogen rate. IWUE also increased with the increase of nitrogen rate, but decreased with the increasing irrigation amount. NUE, UPE and PFP all decreased with the increase of nitrogen rate under different irrigation conditions, and NUE and UPE were significantly inhibited with the nitrogen rate increasing. Under W2 and W3 levels, When the nitrogen rate reached N2 treatment, continuing to increase nitrogen rate, NUE did not change significantly. Reducing nitrogen rate appropriately could significantly increase PFP. For the same nitrogen rate, UPE increased significantly with the increasing irrigation amount.(6)Nitrogen accumulation in various organs of cucumber appeared "S" type with the growth progress, and obtained maximum cumulated amount at full bearing period. At different growth stages, nitrogen accumulation in different organs of cucumber showed the situation of leaf> stem> root, and nitrogen uptake in fruit reached the maximum at harvest period, and plant nitrogen uptake increased with the increasing Irrigation amount and nitrogen rate. The nitrate nitrogen content in the soil continued to accumulate with the growth progress, and migrated downward continuously. Irrigation and nitrogen amount had important impact on soil nitrate nitrogen distribution, and nitrogen rate was a key factor in soil nitrate nitrogen accumulation. Nitrate nitrogen content in surface soil gradually decreased with the increasing irrigation amount, whereas gradually increased with the nitrogen rate increasing. The higher nitrogen rate was more likely to result in nitrate nitrogen leaching, and generate accumulation at the lateral boundary of the wetted volume.