WaterSubject

Cotton Gossypium spp.is a major crop grown throughout many arid regions of the world.Because large quantities of irrigation water are needed to producecotton in these regions, achieving maximum crop productivity per unitof applied water has become critical as costs for water and constraintson water availability increase. Findings from a number of previousfield investigations conducted in the desert southwestern U.S. andother arid locations suggest that final lint yields for cotton areoften greater when the irrigation interval is shorter . summarized the results from a body of research studies that evaluatedcotton yield response to different irrigation cycles, each heldconstant for an entire season. Based on that literature, which involvedboth pressurized and surface irrigation systems, concluded that cotton yields decrease by about % on average for eachday added to the irrigation interval. Although the basis for the yieldeffect due to irrigation frequency is not well defined, it has beensuggested that extended irrigation intervals create cyclical plantwater stress which limit the production potential of the crop .Adverse effects on cotton yields are generally more pronounced whenwater stress occurs during the reproductive stage than duringvegetative growth . suggested that long irrigation cycles during the fruiting periodreduces the effectiveness of the root system to transport water andnutrients to plant leaves. Nutrient stress during boll load oftenhastens the cessation of flowering , and may be also associated with excessive fruit shed .Dripand subsurface drip irrigation methods are considered ideal forapplying small, highly frequent deliveries of water to crops .A number of field tests have compared cotton grown under both driphigh frequency and surface irrigation low frequency. Trialsreported by , , , , and indicated that high frequency drip irrigation can result insignificantly greater cotton yields than those attained under lessfrequent irrigation with surface irrigation methods. However, asevidenced by the works of , , and ,lint yields comparable to those under highly frequent drip irrigationhave been achieved with efficiently designed surface irrigation systemswhen irrigation management resulted in minimum soil water deficits.Providingmore frequent irrigations with surface irrigation methods has beenproposed as a means to increase cotton productivity in cases where dripirrigation or other pressurized systems are not economicallyjustifiable . However, information on the effects of high frequency surface irrigation on cotton yields is limited. Studies by revealed that the water relations of cotton plants were highlydependent upon the frequency of irrigation when the fruit load washeavy, but were generally independent of frequency before and after theperiod. Thus, they hypothesized that by confining frequent irrigationsto the period of rapid fruiting, surface irrigation methods could beused to enhance cotton yields to the degree often associated with highfrequency drip irrigation. Later, tested the hypothesis in a two-year study conducted on a sandy loamsoil in central Arizona. By applying flood irrigation to plots morefrequently about every five days during a threeâ??four week periodcoinciding with rapid fruiting, lint yields for an indeterminateshort-staple cultivar were increased by an average of % over yieldsfor control plots irrigated at â??-day intervals but with the sameamount of total applied water. conducted a similar study on a silty clay in the California desertusing furrow irrigated cotton. In their study, equal volumes of totalwater were applied during the peak fruiting period but withdifferential frequency intervals of five, , and days. Lint yieldsunder the five-day frequency were consistently higher than yields underthe -day frequency, with an average increase of .% over three yearsof study. Thus, the effect of irrigation frequency on yield responsefrom was considerably smaller than that from . In studies with level basins, using a season-long irrigation frequency of seven days realized anaverage lint yield increase of % over a -day irrigation interval ina three-year study in Arizona.Because of the limited informationavailable on cotton responses to high frequency surface irrigation, aswell as disparity in the reported yield advantage achieved underfrequent irrigation, we conducted a two-year study with cotton grownunder three irrigation frequency treatments in level basins. Theobjective was to determine the effects of surface irrigation frequencyon the growth, lint yield, and water use responses of asemi-determinate cotton cultivar in the Sonoran desert of Arizona.