The Effect Of Drip Irrigation Emitter Density And Irrigation Level On Tomato Root Distribution,Yield And Quality

China is one of the world’s largest producers of vegetables.Drip irrigation is a technology that is being adopted worldwide and has a ton of potential in terms of increasing water use efficiency,yield,and fruit/vegetable quality.The plants uptake water from a wetting zone produced by drip irrigation,but traditional drip irrigation activates only a side of the root zone.Because the root zone is reduced due to channeling effects under a single emitter per plant,plants have less soil water storage for their growth.Root water and nutrient absorption and interception are reduced as a result of this channeling activity,decreasing yield and water use efficiency.If soil moisture and root distribution uniformity are increased using a greater number of emitters per plant,the soil moisture status can be improved.Crop yield and water use efficiency can be enhanced,and groundwater pollution can be reduced by increasing root absorption and interception of water and nutrients through increased root distribution uniformity.Little research has been done on the root–shoot and saline ion concentration relationships for potted gerbera and weeping fig under varying salinity,irrigation,and drip emitter density conditions.However,the effects of the drip emitter density（number of emitters per plant）and irrigation levels on the soil moisture and root distributions,and root growth concerning shoot growth,plant physiology,fruit yield/quality and water use efficiency for greenhouse-grown cherry tomato crops are yet to be known.Meanwhile,increasing emitter density has the side effect of raising system costs.Whether the coupling emitter density and irrigation levels would improve vegetable productivity and quality to achieve the optimum levels of profit,we must study four aspects under varying emitter density and irrigation level:soil moisture and root morphological distributions,shoot morphological and physiological parameters,fruit yield and fruit quality,relationships between root and shoot,and optimization scheme.The randomized complete block design technique was adopted by selecting eight treatments with two irrigation regimes（full:100%and deficit:75%of crop evapotranspiration）and four levels of emitters（1,2,3 and 4）under greenhouse conditions.We experimented on the tomato for two successive spring-summer（SS）and fall-winter（FW）growing seasons under greenhouse conditions.Following are the findings of this study.（1）Soil moisture and root distribution regularity under different emitter density and irrigation levelIn this study,root growth,soil moisture distribution and root distribution improved with emitter density and decreased with deficit irrigation.The treatment T4:N4W1（4 emitters per plant and 100%irrigation）had the greatest increase in root length（42.79%for SS and 41.14%for FW）,root fresh matter（26.70%for SS and 45.65%for FW）,root dry matter（6.56%for SS and 12.86%for FW）,specific root length（34 and 25.06%for SS and FW,respectively）,root fineness（1.5 and1.24%for SS and FW,respectively）,and root water uptake（26.56 and 29.94%for SS and FW,respectively）when compared to T1:N1W1（single emitter per plant and 100%irrigation level）.When compared to T1:N1W1,T5:N1W2（single emitter per plant and 75%deficit irrigation）showed the greatest increase in root average diameter（3.02 and 0.28%for SS and FW,respectively）and root tissue density（0.40 and 13.29%for SS and FW,respectively）.Compared with the control T1:N1W1,the highest decrease in soil evaporation（47.21 and 51.25%for SS and FW,respectively）was recorded for T8:N2W2（four emitters per plant and 75%deficit irrigation）.In this study,increased emitter density has a two-fold effect on soil moisture and root distribution.It increases emitters per plant while lowering the emitter flow rate to keep the same flow rate per plant.Soil moisture and root distributions spread horizontally and moved upwards vertically as emitter density was increased,which favors higher root water and nutrient uptake.Deficit irrigation resulted in shallower and reduced moisture and root concentrations,with some of the roots penetrating deeper in the soil profile in search of moisture.The two emitters have increased the soil moisture area（horizontal:80%and vertical:32%）and root growth area（horizontal:45%and vertical:52%）over a single emitter per plant.There were observed significant（P<0.001）relationships between moisture and root distributions with R² ranging from 0.567 to 0.678 for FW.The T6:N2W2 treatment（two emitters per plant with 75%deficit irrigation）had an optimal root distribution of all treatments,with an average root length density of 1.1 cm cm^-3 and root weight density of 77.7μg cm^-3.Its root dispersion range was wider horizontally across the entire pot and deeper vertically throughout the soil profile.It was concluded that as emitter density increased the decreasing soil evaporation resulted in increased soil moisture and root growth areas and increased root water uptake,which may be considered the key factor promoting increased yield.（2）Responses of shoot growth and physiological parameters under drip emitter density and irrigation levelAll shoot growth and physiological parameters increased with emitter density and decreased with deficit irrigation except instantaneous water use efficiency that increased with both emitter density and deficit irrigation for both seasons.The highest increase in the total fresh matter（19.82and 17.71%for SS and FW,respectively）,total dry matter（14.58 and 18.92%for SS and FW,respectively）,plant height（17.89 and 22.45%for SS and FW,respectively）,stem diameter（11.87and 10.21%for SS and FW,respectively）,leaf area index（32.93 and 31.77%for SS and FW,respectively）,photosynthetic rate（19.52 and 18.66%for SS and FW,respectively）,transpiration rate（12.16 and 9.33%for SS and FW,respectively）,stomatal conductance（23.99 and 29.20%for SS and FW,respectively）,and leaf intercellular CO2 concentration（20.55 and 20.82%for SS and FW,respectively）were observed against T4:N4W1 when compared with the control T1:N1W1.The highest increase in instantaneous water use efficiency（12.48 and 22.32%for SS and FW,respectively）was recorded against T8:N4W2 when compared to T1:N1W1.It was concluded that increasing emitter density under a limited water supply could increase tomato shoot growth and physiological parameters.（3）Effects of drip emitter density and irrigation level on yield,water use efficiency,fruit morphological and quality parametersFruit yield and fruit morphological parameters increased with emitter density and decreased with deficit irrigation.Water use efficiency increased with emitter density and deficit irrigation.Total soluble solids decreased with emitter density and increased with deficit irrigation,and vice versa was for p H.The highest increase in yield（24.15%for SS and 15.43%for FW）,harvest index（3.62 and 1.87%for SS and FW,respectively）,fruit unit dry weight（5.86 and 9.04%for SS and FW,respectively）,fruit number per plant（17.29%for SS and 5.86%for FW）,fruit diameter（8.70 and 6.70%for SS and FW,respectively）and fruit height（5.47 and 2.11%for SS and FW,respectively）were observed against T4:N4W1 when compared to the control T1:N1W1.Compared with the control T1:N1W1,the highest increase for water use efficiency（54.59 and48.57%for SS and FW,respectively）and water use efficiency biomass（53.90 and 48.04%for SS and FW,respectively）values were recorded against T8:N4W2.The highest increase in total soluble solids（13.74%for SS and 14.94%for FW）were recorded for T5:N1W2,while that for p H（0.48 for SS and 0.73%for FW）was recorded against T4:N4W1 when compared with T1:N1W1.It was determined that,under limited water conditions,increased emitter density might be used to minimize the negative impacts of deficit irrigation while also enhancing tomato fruit yield.（4）The relationships between root with shoot and yield,and the optimization of drip emitter density and irrigation levelAll the relationships between root growth parameter with shoot growth parameter and yield were significant（P<0.001）,with R² ranging from 0.543 to 0.965（simple linear regression）and from 0.782 to 0.954（multiple linear regression）.Further,there were observed linear and quadratic relationships.The highest increase in root shoot ratio（0.50%for SS and 1.50%for FW）was observed for T5:N1W2 when compared with T1:N1W1.The highest increase in total costs（32.80and 43.62%for SS and FW,respectively）and total benefits（24.15 and 15.43%for SS and FW,respectively）were observed for T4:N4W1 when compared with T1:N1W1.The highest increase in net benefits（25.34 and 11.53%for SS and FW,respectively）and benefit-cost ratio（30.19 and16.91%for SS and FW,respectively）was observed for T6:N2W2 when compared with T1:N1W1.Targeting total costs,yield,fruit quality and water use efficiency,based on the performance score Pi of TOPSIS for multi-objective optimization of irrigation emitter density and irrigation level,is optimal T6:N2W2（Pi:0.826 and 0.808 SS and FW,respectively）.It was concluded that as the emitter density increases,a positive root-shoot correlation can be achieved,and T6:N2W2treatment is the recommended strategy for greenhouse tomato water management.Summarizing all:the increased emitter density has increased soil moisture distribution uniformity,root distribution uniformity and root morphological parameters（root length and root dry matter）.This resulted in improving shoot morphological and physiological responses,increasing fruit yield and quality,and improving root shoot relationships.Two emitters per plant and a 75%irrigation level were observed as optimal for greenhouse-grown cherry tomatoes.This treatment resulted in the highest benefit-cost ratio with a higher yield,WUE and fruit quality.This research comprehensively considered the effects of variable emitter density,irrigation level and season on the soil moisture and root distributions of cherry tomatoes grown in greenhouses,and the root growth concerning shoot growth,plant physiology,fruit yield/quality and water use efficiency.It will supply an irrigation technology that improves yield,WUE and fruit quality by suppressing the adverse effects of deficit irrigation.Innovations:（1）The regularity for soil moisture and root distributions under varying drip emitter density and irrigation level was explored.It was seen that increased emitter density could improve root distribution uniformity and root morphology of cherry tomatoes grown in greenhouses.（2）The optimization method of emitter density and irrigation level based on multi aims of the yield,fruit quality,water use efficiency,and the total cost was proposed.It was found that the two emitters per tomato plant are optimal.It could significantly improve tomato yield,water use efficiency and fruit quality.