CONE INDEX AND ROOT-GROWTH IN SURFACE AND SUBSURFACE MICROIRRIGATED HARDPAN SOIL

Restricted root growth caused by subsurface hardpans and low water hol ding capacity reduces crop yields in many United States southeastern C oastal Plain soils. With intensive irrigation it is possible to obtain suitable yields without deep tillage. The objective of this study was to find differences of root growth and cone indices between surface a nd subsurface applied sources of irrigation water. We measured root gr owth and cone index in intensively managed irrigation plots of green b eans (Phaseolus vulgaris L.) in 1988 and 1989. Microirrigation tubes w ere placed on the surface or in the subsurface - buried at a depth of approximately 0.25 m - and irrigated either continuously or with inter mittent pulses of water. Mean profile cone indices for the surface tub e placement were significantly lower than for the subsurface tube plac ement. Mean profile cone indices for the continuous irrigation treatme nt were significant lower than for the intermittent irrigation treatme nt. However, no one treatment significantly reduced the cone indices w ithin the hardpan. Total root count was significantly greater for the subsurface tube placement with increased root growth below the 0.1-m d epth. There was a high density of roots next to the subsurface tube th at would have been effective in uptake of water from the microirrigati on tube. However, yield was significantly greater for the surface tube placement. For all treatments, the largest concentration of root grow th occurred in the top 0.2 m of the soil within the row. We expected t his for the surface irrigation treatment. However, we also measured th is for the subsurface treatment, probably because of high rainfall and upwelling of water from the subsurface micro-irrigation tube.