| Due to the shortage of water resources,groundwater is seriously overexploited in Hebei Province.Meanwhile excessive water and fertilizer application has a negative impact on the sustainable development of protected vegetable industry.How to improve both fertilizer and water use efficiency is one of the essential strategies to achieve the goals of sustainable agriculture.Greenhouse watermelon is an important economic crop in the region.However,there is still a lack of research about efficient water and fertilizer management technology and mechanism research.The trial was conducted in 2016 and 2018.The suitable root-soil space of facility watermelon was studied.The water requirement law of watermelon under negative pressure infiltration irrigation was clarified,and the evapotranspiration model of watermelon was established.Under the condition of negative pressure and different water supply suction,the sensitive period of water demand,sensitive index and irrigation threshold of different growth stages were determined.The effects of different fertilizer rates on growth,dry matter accumulation characteristics and nutrient accumulation and transportation of watermelon were studied,under these irrigation indexes.The results are as followed.1.The effects of different root-soil space treatments(10 cm,20 cm,30 cm,40 cm,50 cm and control 100 cm(CK))on the growth,yield and quality of greenhouse watermelon were studied.The results showed that the yield of watermelon increased with the increase of root-soil space in 10 to 40 cm.While,there were no significant differences in growth,yield and quality between 40 cm,50 cm and CK.Therefore,the root-soil space for watermelon should be 40 cm at least.2.The effects of four levels of negative water pressure(-5,-10,-15,-20 kPa,corresponding to 96%,80%,72%,63%)on evapotranspiration characteristics of greenhouse watermelon were studied.The results showed that the diurnal variation of watermelon evapotranspiration showed a single peak curve,and the evapotranspiration in sunny days was greater than that in cloudy days.In 2016 and 2018,the daily average evapotranspiration was 1.15 mm/d and 1.34 mm/d at the vine extension stage,2.80 mm/d and 3.27 mm/d at the flowering and fruit setting stage,and 3.61 mm/d and 4.67 mm/d at the fruit expansion to mature stage.The characteristics of water demand in the whole growth period were as follows:the daily average evapotranspiration gradually increased from the vine extension stage to the fruit expansion to mature stage,and then decreased.3.The evapotranspiration of watermelon was significantly affected by meteorological factors,when the soil water content is sufficient.Watermelon transpiration was positively correlated with reference crop evapotranspiration(ET0),daily mean air temperature(T)and daily photosynthetic photon flux density(PPFD),and negatively correlated with daily mean air relative humidity(RH).According to the correlation degree,the order was ET0>PPFD>RH>T in 2016 and ET0>T>RH>PPFD in 2018.The influence of meteorological factors on watermelon transpiration was different in 2016 and 2018,while ET0 showed stable correlation coefficients with the transpiration in 2 years.The results showed that the evapotranspiration of watermelon was mainly affected by the comprehensive atmospheric factors.4.The evapotranspiration of watermelon was significantly affected by soil moisture.When the soil water content is sufficient,the evapotranspiration of watermelon is mainly affected by meteorological factors.When the soil water content is insufficient,the correlation between the evapotranspiration of watermelon and meteorological factors decreases.The threshold value of negative pressure water supply for evapotranspiration of watermelon in different growth stages was 72%in vine extension stage and flowering and fruit setting stage,and 80%in fruit expansion to mature stage.The change trend of watermelon crop coefficient is a significant parabolic with the increase of accumulated temperature.Therefore,combined with accumulated temperature and improved P-M equation,a watermelon evapotranspiration model was established.The average relative error and absolute error of the model are 18.42%and 0.61 mm/d respectively.The simulation results can be used to estimate the evapotranspiration of local watermelon.5.In 2016 and 2018,the yield of-5 kPa and-10 kPa treatments at vine extension stage were 34.3 t/hm2 to 36.6 t/hm2.The highest water productivity(WP)was-5kPa treatment.The yield of-5 to-15 kPa treatment at flowering and fruit setting stage were 33.9 t/hm2 to 38.0 t/hm2,and the WP were 18.2 to 22.1 kg/m3,which were no significant difference among the three treatments.The highest yield of-5 kPa treatment at fruit expansion to mature stage was 40.5 t/hm2 in 2016 and 39.7 t/hm2 in 2018,which was significantly higher than other treatments,while there was no significant difference in WP among the treatments.At flowering and fruit setting stage,the content of soluble sugar and soluble solid in-20 kPa treatment was the highest,and the content of organic acid was the lowest,followed by-10 kPa and-15 kPa treatments.The contents of soluble sugar,protein and soluble solids were the highest in-10 kPa treatment at fruit expansion to mature stage.The water sensitivity index of watermelon at vine extension stage,flowering and fruit setting stage and fruit expansion to mature stage were 0.463,0.325 and 0.700 respectively,adopting Jensen Model.The results showed that the most sensitive period to water was fruit expansion to mature stage,followed by vine extension stage,and the least sensitive period was flowering and fruit setting stage.6.The results showed that the maximum mineral nutrient accumulation was obtained when the fertilization amount was N 155.0 kg/hm2,P2O5 62.0 kg/hm2,K2O 201.0 kg/hm2.At final harvest,the accumulation of N,P and K were 130.83 kg/hm2,26.08 kg/hm2 and 112.45 kg/hm2,respectively.The fertilizer use efficiency was 40.81%,20.52%and 26.73%respectively.With the development of watermelon,the accumulation pools of nitrogen,phosphorus and potassium in different organs changed from leaves to fruits.The accumulation of N,P and K in leaves was 69.90%to 75.18%,59.84%to 64.26%and 48.35%to 52.42%of the total plant accumulation before flowering and fruit setting stage,respectively.The fruit became the center of nutrient accumulation after the expansion stage,and the accumulation of N,P and K in the fruit accounted for 62.98%to 69.73%,66.07%to 72.08%and 74.49%to 77.21%of the total accumulation of the whole plant,respectively.The accumulation of N,P and K in the whole plant of watermelon were fitted with the Logistic equation.The rapid accumulation period of N was 41～42 days after planting,the rapid accumulation period of P was 42～44 days after planting,and the rapid accumulation period of K was 50～55 days after planting.The N accumulation of the whole plant in the period of vine extension flowering fruit setting,flowering fruit setting maturity and maturity harvest accounted for 30.01%～33.59%,61.35%～66.82%and 2.81%～5.12%of the total N accumulation in the whole growth period,respectively.The P content was 24.44%～27.42%,64.88%～71.43%and 1.27%～9.59%,and the K content was 19.96%～23.21%,54.05%～61.31%and 17.23%～24.13%.Therefore,watermelon should be fertilized in the vine extension stage and the fruit expansion stage.The average ratio of N,P and K in the vine extension stage and fruit expansion stage are 1:2.2,1:2.8 and 1:3.6,respectively.Compared with the contribution proportion,the maximum contribution proportion of nutrient organs to fruit nutrients was 15.44%for N,7.04%for P and 5.10%for K.The results showed that 84.56%of nitrogen,92.96%of phosphorus and 94.90%of potassium were absorbed by the fruit itself,so it was necessary to supply fertilizer synchronously according to the characteristics of watermelon growth period.7.The results showed when the fertilization rate was N 155.0 kg/hm2,P2O5 62.0 kg/hm2,K2O 201.0 kg/hm2,the leaf area,photosynthetic characteristics and dry matter accumulation of watermelon were significantly increased.The yield was the highest,which was 34600 kg/hm2,and fruit quality was significantly improved.The dry matter accumulation of watermelon was fitted with the Logistic equation.The rapid accumulation period occurred in 49 to 51 days after planting,and the maximum accumulation rate was 5.73 to 8.63 g·plant-1·d-1.8.The water and fertilizer management system is determined.The most suitable irrigation depth is 40 cm.The irrigation threshold of different growth stages was 80%of soil relative water content in vine extension stage,72%of soil relative water content in flowering and fruit setting stage,and 80%of soil relative water content in fruit expansion to mature stage.The fertilization amount was N 155.0 kg/hm2,P2O5 62.0 kg/hm2,K2O 201.0 kg/hm2.The average ratio of nitrogen,phosphorus and potassium in the vine extension stage and the fruit expansion stage are 1:2.2,1:2.8 and 1:3.6.Compared with the traditional water and fertilizer management,the irrigation amount decreased by 32.62%,the yield increased by 13.37%,the irrigation water use efficiency increased by 68.20%,the partial factor productivity of nitrogen,phosphorus and potassium increased by 46.27%,46.27%,and 46.63%,respectively.And the fruit quality improved significantly,economic benefit increased by 10.68%.This technology improves the utilization efficiency of water and fertilizer and economic benefits. |
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