-Subsurface drip irrigation can reduce off-farm movements of fertilizers and pollutants and improve the water use efficiency of irrigated agriculture. Here we compared the effects of furrow and subsurface drip at different irrigation rates, based on a percentage of daily crop-evapotranspiration rates (ETc), on run-off and off-site movement of suspended sediment, nutrients and pesticides from cotton crops grown on a vertisol. Our results show that furrow irrigation significantly increased suspended soil loss, of 5.26 t ha −1 , compared to that of subsurface drip irrigation at 120% of ETc, of 2.53 t ha −1 , whereas no erosion was recorded with deficit subsurface drip irrigation. Off-site movement of nitrogen in furrow, of 18.63 kg ha −1 , was five times greater than subsurface drip irrigation at 120% ETc. It was much less with 105% ETc (0.37 kg ha −1 ) and 90% ETc (0.15 kg ha −1 ), and absent for 75% and 50% of ETc. Phosphorus loss from furrow, of 778 g ha −1 , was greater than for the wetter subsurface drip treatments that gave 23 g ha −1 for 90% ETc and 19 g ha −1 for 120% ETc. No P loss was recorded from drier subsurface drip irrigation rates. Herbicides such as atrazine and diuron were applied in the year prior to the experiment, but considerable amounts were recorded in furrow run-off in both years, but only at 90 and 120% ETc subsurface drip irrigation in the first year. Concentrations of applied herbicide residues in the runoff exceeded the minimum threshold level for 99% species protection and, although the total amount of herbicide movement was higher in furrow, at times the concentration was greater for wetter subsurface drip irrigation run-off. Residues of insecticides, such as endosulphan applied in a previous year and dimethoate applied in the current years, were recorded in runoff from subsurface drip at 120% and furrow irrigation. Their concentrations in each year exceeded minimum threshold level. Subsurface drip irrigation at 75% ETc offered the best trade-off between off-site run-off, erosion and pesticide movement and yield and water use efficiency.Furrow / subsurface drip / run-off / erosion / herbicide/ nitrogen / phosphorus

The practice and management of subsurface drip irrigation (SDI) on heavy clay soils is poorly understood. Over-irrigation can lead to excessive runoff and drainage, with associated negative environmental consequences. Experiments were conducted in 2001/2002 and 2002/2003 on cotton (Gossypium hirsutum) in a Vertisol in Australia to evaluate the effect of SDI at various application rates on cotton yield and quality, and the results were compared with those for conventional furrow irrigation. Irrigating with SDI that supplied 50% or 75% of daily crop evapotranspiration (ETc) maintained a dry upper soil profile throughout the season. SDI at 50% ETc could potentially capture 250mm more rain during the season compared to SDI 90% ETc, and even more than furrow irrigation. However, supplying only 50% ETc with SDI hastened the maturity of the crop by on average 25 days compared with furrow irrigation and higher SDI rates, fewer bolls were set and yields were lower than in the other treatments. Nevertheless, a shorter season, if yield sacrifice is acceptable, favours logistics when integrating winter crops with summer cotton. It also reduces the number and cost of pesticide sprays and irrigation. Yield plateaued when 75% or more of daily ETc was supplied by SDI. The two drier treatments (SDI at 50% and 75% of ETc) had consistently higher water use efficiencies (WUE) for lint production compared with those of the two wetter SDI treatments (SDI at 90% and 105/120% ETc). All SDI treatments were also more efficient in the first year in the use of water for lint production than was furrow irrigation, but improved irrigation management in the form of faster irrigation and reduction of tail water in the second year obviated the advantage of SDI. Irrigation of cotton with SDI at 75% ETc offered significant benefits in terms of saved irrigation water over wetter SDI treatments, resulted in the highest average WUE for lint production over the two years, and reduced drainage and runoff compared with higher SDI rates and furrow irrigation.