| It is the important content of irrigation study to determine the proper lower limit index of soilmoisture in irrigation technology system, which decides the starting time and frequency of irrigation,affects the amount of irrigation, and is the significant base for setting water demand of crop andreasonable irrigation. When monitoring soil moisture content, setting position and quantity ofmonitoring spots have direct influence on the accuracy of area soil moisture content, plus theobjective existence of spatial variability of soil moisture content, therefore it’s very important todecrease the amount of samples to the greatest extent through scientific and reasonable samplingspots setting under the premise of certain accuracy. At present, the area applied drip-irrigation inXinjiang has been up to over37million Mu. According to the result of literature novelty search, theresearch and application of drip-irrigation control index mainly surrounds greenhouse vegetables orflowers. But for the field drip-irrigation cotton under film, the research of the relation betweendifferent lower limits of soil moisture and cotton growing and final yield is sill incomplete, and theresearch of quantity and position of monitoring spots in field lacks of actual verification, which justdivides contour map into different zones and sets monitoring spots within each zone or merely putsforward range of the zone. Therefore, researches under three different planting modes, such as thesetting positions and amounts of soil moisture content monitoring spot, the effects of different soilmoisture lower limits under different growth stage on cotton yield and utilization rate of water, realtime forecast of soil reservoir moisture content, are committed with SHIHEZI irrigated area as thecore testing area. Through the test research for three years, the following conclusions can beobtained:⑴Monitoring spots setting in wetness body was put forward: lateral spots setting, it’sappropriate to set the monitoring spots within the area250mm to550mm away from the dripirrigation tape under the model of one film and one pipe, it’s appropriate to set the monitoring spotswithin the area150mm to450mm away from the drip irrigation tape under the model of one film andtwo pipes and four rows, it’s appropriate to set the monitoring spots within the area250mm to450mm away from the drip irrigation tape under the model of one film and two pipes and six rows.Longitudinal spots setting, the soil moisture contents in different depth have higher linear correlation,the less the gap between different layers, the higher the correlation, so it’s appropriate to decreasethe setting amounts of soil moisture sensors reasonably. For class3, it’s appropriate to set threesensors altogether in the layers of20cm,40cm and60cm. For class2, it’s appropriate to set twosensors altogether in the layers of20cm and60cm.⑵Influence factors on layout of the monitoring points in field scale were analyzed:①The results showed that there are the influence of different sampling modes which wasuniform distributed points or random distributed points on reasonably determining sampling number.The changes of mean values and coefficients of variation (CV) in the condition of uniformdistributed points were more significant than that in the condition of random distributed points.Compared with the other data, the change rates of soil moisture which gained by two samplingmodes were within3%, and the test precision could be attained to design requirements. So the twosampling modes were all feasible.②The results showed that there are the influence of differentsampling spaces on reasonably determining sampling number. The variability of soil moisture invertical direction with drip irrigation tape was more than that in parallel direction with drip irrigation tape.③The results showed that there are the influence of different precisions on reasonablydetermining sampling number. The reasonable sampling number was increased with relative error kdecreased at the same confidence level;The reasonable sampling number was increased withconfidence level raised under a given relative error k; The reasonable sampling number wasincreased with the coefficients of variation of soil moisture raised under given simultaneouslyconfidence level P and relative error k.④The results showed that there are the influence of differentsampling times on reasonably determining sampling number. The variability of soil moisture indifferent layers was belonging to weak variability or moderate variability, and the coefficients ofvariation before irrigation is higher than that after irrigation.⑤The results showed that there are theinfluence of different soil textures on reasonably determining sampling number. The coefficients ofvariation showed an increasing tendency with the field area enlarged at the same soil texture;Thecoefficients of variation decreased with sampling error increased at the same monitor time andconfidence level;The coefficients of variation reduced with confidence level decreased at the samemonitor time and sampling error.⑶The quantity and location of the monitoring points in field scale were initially determined:It was obvious advantages that applying Kriging method to determining reasonable samplingnumber compared with the traditional statistics method. Because the higher precision could begained with less sampling number, and the sampling efficiency was improved about4times whenapplying Kriging method.⑷Water consumption regularity of soil moisture content under different irrigation thresholdwere analyzed: Variation coefficients in the layer from0to20cm and the layer from20to40cm areboth over0.1, which are middle-level variation. Variation coefficients in the layer from40to60cm,the layer from60to80cm and the layer from80to100cm are below0.1, which are weak variation.Variable amplitude of soil moisture content in crop root zone differs along with time, maximum inbud stage, medium in seedling stage, minimum in blooming and boll-forming stage. Within thewhole period of duration of cotton, the total water-consumption amount ranges from404.84mm to530.59mm and the average water-consumption strength ranges from2.44mm·d-1to3.27mm·d-1.⑸Irrigation threshold value of drip irrigation cotton was initially determined:①as for cottonyield, the lower limits of optimum soil moisture indexes are55%～60%、65%～70%、75%～80%、60%～65%of soil moisture capacity at the stage of seeding, squaring, flowering,boll-opening of cotton plant, respectively.②as for water use efficiency, the lower limits ofoptimum soil moisture indexes are60%～65%、65%～70%、80%～85%、55%～60%of soilmoisture capacity at the stage of seeding, squaring, flowering, boll-opening of cotton plant,respectively.③The different values of lower limit of irrigation could be adopted according torequired goal when making irrigation regime of Shihezi irrigation area. If the water inflow inirrigation area was less, the lower limit value in different growth stages which was set with the fifthtreatment should be used to get to more water use efficiency. If the water inflow was abundant, thelower limit value in different growth stages which was set with the second treatment should be usedto get to higher cotton yield and more economic benefit. |
PDF Full Text Request