Physiological and yield responses of cotton under partial rootzone irrigation

Partial rootzone irrigation (PRI) means that part of the root system is exposed to drying soil while the remaining part is irrigated as in full irrigation. The wetted and dried sides may be shifted according to the soil drying rate and crop water requirement. The hypothesis is that such irrigation may save water without much reduction in economic yield in field crops such as cotton. We therefore designed a field experiment in an arid area where cotton production almost completely relies on irrigation. Water was applied to furrows in the cotton field either alternatively (alternative furrow irrigation, AFI), evenly to all the furrows (conventional furrow irrigation, CFI) or to one fixed furrow in every two (fixed furrow irrigation, FFI). PRI (AFI and FFI) saved up to 30% irrigated water but produced comparable numbers of opened bolls per plant. The total seed cotton yields of AFI and FFI were 92 and 84%, respectively, of that of CFI, but AFI produced 12% more the first and second harvest seed cottons before the frost (i.e. higher quality fibers for better price) than the CFI. Stomatal conductance was lower in AFI and FFI than in CFI in the early days after each irrigation but leaf water potential was comparable among the three treatments during whole crop season. The AFI and FFI plants produced less leaf area and shorter plants than CFI but the bud numbers per plant showed no significant difference. We concluded that AFI is an effective water-saving irrigation method in arid area and plant vegetative growth can be controlled by the irrigation such that seed cotton yield can be maintained with less water but higher quality fibers.