Soil conditions affect cotton root distribution and cotton yield under mulched drip irrigation

Film-mulched drip irrigation with brackish water has been used widely for cotton (Gossypium hirsutum L.) production in arid regions. Full consideration of the promise of brackish water irrigation requires consideration of the dependence of cotton root characteristics on soil conditions. To date, these dependences are complex and poorly understood. The present study compared the impacts of soil temperature, water and salinity on root characteristics on cotton yield for brackish water irrigation treatment (BWT) and fresh water irrigation treatment (FWT). Spatial differences were observed for cotton root mass, root length, root surface-area and root volume distribution that corresponded with differences in the distributions of soil conditions. There existed a strikingly linear relationship between cotton root length and root mass. Soil temperature did not exert clear control on root system growth. Lower average root density and coarser roots were observed for BWT than for FWT as a result of the reduced soil temperature and the elevated soil salinity associated with BWT. Cotton shoot growth was more sensitive than root growth to salt stress for BWT. Higher root density and fine root proportion for FWT than BWT led to higher cotton yield. That is, more cotton roots were observed in the shallow mulched zone, which corresponded with high root water uptake rate and salt accumulation. Our study indicated that the easily-measured cotton root mass could be used as a practical surrogate for root length under mulched drip irrigation. Subsurface drip irrigation with drip tapes set in the shallow mulched zone may further promote cotton root system growth, allowing for sustainable cotton production with brackish water irrigation.