Study On Photovoltaic Drip Irrigation Technology Adapted To Kiwifruit Rain-Shelter Cultivation

Traditional photovoltaic power generation occupies cultivated land resources,while it’s of forward-looking significance to combine photovoltaic power generation with crop rain-shelter cultivation to solve the conflict between photovoltaic land and agricultural cultivated land.In this paper,Jinyan kiwifruit was selected as the research object,and the photovoltaic（PV）coverage ratio was set as19.8%（T1）,31.6%（T2）,39.5%（T3）and open-field cultivation（CK）.In order to find out the effects of different PV coverage ratios on the growth rhythm,yield and quality of kiwifruit,the growth rhythm,photosynthesis,yield and quality of kiwifruit were tested by Li-6400XT,SPAD and other instruments.In the area where there was no grid power supply for irrigation,in order to explore the integration and application of the PV drip irrigation system,the DC voltage,current and power of the PV array output,the pressure and the flow rate of irrigation head system and the field irrigation uniformity were measured and analyzed.At the same time,in order to explore the environmental and economic benefits of integration of photovoltaic power generation and kiwifruit rain-shelter cultivation under the new situation,taking 25 years as a life cycle,the net emission reduction of CO₂-equivalent was systematically analyzed and the economic benefit indicators were also analyzed and calculated.Based on the above tests and analysis,the following results were obtained:（1）The effects of different PV coverage ratios on the growth rhythm of kiwifruit were revealed.There was no significant difference in the SPAD value of kiwifruit,the diameter of new shoots at the end of growth period,and the cumulative growth length of new shoots before pinching.At the end of growth period,the SPAD value was generally stable at 60±5 and the average new shoot diameter of each treatment was 12.06¹2.21 mm;the average growth rate of new shoots before pinching was2.67².82 cm/d.There was no significant difference in the average area of leaves between T1,T2 and T3 and also without significance difference between T1 and CK.However,the average leaves area of T2 and T3 were significantly higher than CK（P<0.05）.The kiwifruit volume measured of T3 was significantly lower than that of CK when harvested（P<0.05）,and there was no significant difference in kiwifruit volume among T1,T2 and CK.（2）Quantitative comparison of photosynthesis,yield and quality of kiwifruit under different PV coverage ratios.From the average value of photosynthesis daily variation,the net photosynthetic rate（Pn）of T1,T2and T3 compared with CK decreased by 10.99%,18.22%and 40.82%,respectively.The transpiration rate（Tr）of T1 and T2 compared with CK increased by 1.41%and 6.97%,respectively.The Tr of T3compared with CK decreased by 18.24%.The instantaneous water use efficiency（WUE_i）of T1,T2,and T3 decreased by 11.72%,22.72%,and 27.14%compared to CK.There was no significant difference in the yield of T1 and CK kiwifruit.The yield of T2 was 21.89%lower than that of CK（P<0.05）,and the yield of T3 was 38.52%lower than that of CK（P<0.05）.Using the principal component weighting method to comprehensively analyze the quality indicators,the scores of T1,T2,T3 and CK were 98.80,95.68,94.00 and 93.63,respectively.That was to say,photovoltaic rain-shelter cultivation could improve the quality of kiwifruit.As the ratio of photovoltaic coverage increased,the degree of quality improvement gradually decreased.（3）The technical parameters of the photovoltaic drip irrigation system without high reservoir or without batteries in the weak illumination area were optimized.In this paper,photovoltaic arrays were installed south-facing with an inclination of 16°.The pressure compensation emitters had a head range of 10-30 m for normal operation,with a terrain height difference of 5 m,so the adjustable pressure range was 15 m for emitters.For the conditions of 3irrigation districts,the area of each irrigation district was 6667 m²,and the flow rate of the system was10.58 m³/h.The photovoltaic power generation system adopted 11 photovoltaic modules in series to form a string,and a total of 8 strings were connected in parallel（total of 88 components）.Under this condition,the minimum waterhead at the outlet of the head system of irrigation was 17.27 m and the maximum was 32.27 m for the demand of drip irrigation system.The corresponding minimum operating frequency was 33.60 Hz and the maximum operating frequency was 38.61 Hz.（4）The environmental and economic benefits of photovoltaic rain-shelter cultivation of kiwifruit were evaluated.The results indicated that the net emission reductions CO₂-equivalent of CK,T1,T2,and T3 were3.44,88.31,143.93,and 180.74 t hm^-22 year^-1,respectively.The net emission reductions CO₂-equivalent of T1,T2,and T3 were about 26 times,42 times and 53 times of CK,respectively.It was economically feasible to cultivate kiwifruit by photovoltaic rain-shelter because the net present value of economy（ENPV）of T1,T2 and T3 was greater than zero.When considering environmental benefits,the ENPV of CK,T1,T2,and T3 were 277796,292514,686221,and 905938 yuan respectively,and the order of the ENPV was T3>T2>T1>CK;When ignoring environmental benefits,the ENPV of CK,T1,T2,and T3 were 270839,117467,401091,and 547951 yuan respectively,and the order of the ENPV was T3>T2>CK>T1.On the whole,the model of low photovoltaic coverage ratio was weaker in economic resistance to risk,while high photovoltaic coverage ratio led a high reduction ratio on yield of the kiwifruit.Moderate photovoltaic coverage（31.6%）led a small reduction ratio on yield of the kiwifruit while it can increase comprehensive economic benefits.Taking yield,quality,economic and environmental benefits and other factors into consideration,moderate photovoltaic coverage ratio（31.6%）was the best photovoltaic coverage ratio in this paper.