Experimental Study On Soil Water Distribution, Fertilization And Crop Growth Under Drip Irrigation In Naturally-ventilated Greenhouse

The research was conducted in a greenhouse farming system at Yangzhou University, Yangzhou, China, during the August-November 2012, March-July 2013 and September-November 2013 seasons for maize, tomato and cucumber, respectively. The objectives of this research were to; 1) investigate the effect of different drip irrigation water amounts on plant growth, yield and quality traits for the study crops under natural ventilation greenhouse conditions; 2) determine the optimal drip irrigation amounts for the three crops, most suitable nitrogen (N) fertigation dose of maize, water movement in the root zone, and 3) estimate the irrigation water use efficiencies (IWUE) and drip irrigation schedules for the study crops. A semicircular shaped greenhouse with the size of 6 m × 30 m was used, and it was covered with the white polyethylene film and oriented north-south direction. The greenhouse soil was a sandy loam with a pH of 7.1. The FAO Irrigation and Drainage Paper 56 (FAO-56) Penman-Monteith method was used to calculate the crop evapotranspiration (ETc). The maize experimental design was a completely randomized design, including two factors, irrigation and fertilization. The irrigation treatment included four levels; I1=1.25 ETc, I2=1.0 ETc, I3=0.75 ETc and I4=0.50 ETc. The fertilization treatment included three levels:F1=1.25, F2=1.00 and F3=0.75 of the recommended nitrogen (N) dose. For tomato and cucumber, two different experiments were arranged as the randomized block design and completely randomized block design with five irrigation treatments, and each treatment had three replications. The five irrigation treatments for tomato and cucumber were 150 (I150/T150),125 (I125/ T125),100 (I100/T100),75 (I75/T75) and 50%(I50/T50) of ETc respectively.Results of the research indicate that the different irrigation and fertigation treatments significantly affected crops growth, yield and quality traits. For maize, the results showed that deficit irrigation treatment of 0.5 ETc produced the highest yield of 26.8 t/ha and the highest irrigation water use efficiency of 0.209 tha-1mm-1. The deficit irrigation increased the yield by 11.7% over the irrigation control and 8.1% over the excessive irrigation of 1.25 ETc; it also produced a higher ear length of 16.6 cm. The highest nitrogen rate of 125% produced the highest yield of 26.2 t/ha with maximum grain moisture content of 57.2% and 20.4 g of 100-seeds dry weight; and the highest N rate obtained 11% increase in yield over the fertigation control.The tomato experiment results revealed that the drip irrigation at the I100 water level produced the highest marketable yield of 78.6 tha-1 with the irrigation water use efficiency of 0.479 tha-1 mm-1, and it also had a higher values on plant height (125.5 cm) and chlorophyll content (56.4 spad). Similar results were observed for I75 in term of crop quality. The 100% ETc resulted in an increase of the marketable yield by 13.6% over the 75% ETc water level. There were no significant differences between I75 and I100 on total soluble solids (TSS) and fruit shapes index (FSI). For cucumber, the T100 treatment of 100% ETc produced the highest fruit yield of 37.8 t/ha, and the T50 treatment of 50% ETc produced the lowest value of 21.2 t/ha.For different irrigation levels, the T100 treatment achieved the highest yield, and it was 39%,27.7%,3.9% and 1.3% more than the T50, T75, T150 and T125 treatments, respectively. In terms of growth parameters and quality traits, the T100 resulted in the highest values in leaf area index (LAI) and the leaf chlorophyll, fruit number per plant, fruit length and fruit weight. The maximum irrigation water use efficiency was 0.340 tha-1mm-1, which was obtained for the T50 of 50% ETc treatment, while the lowest efficiency was 0.152 tha-1mm-1 from the T150 of 150% ETc treatment.Based on this study, we conclude that, the fertigation rate of 125%(F1) is the best option to maximize maize yield and improve product quality. Under drip irrigation, the deficit irrigation of 0.50 ETc for maize experiment, and 1.00 ETc for tomato and cucumber are the most suitable irrigation amounts to maximize the yields and improve the quality traits.