Farm Table says:
What is the problem?
The objective of this study was to quantify the effects of tillage methods and the summer crops of cotton , maize, and sorghum on fine root number density in the non-sodic sub-surface and sodic subsoil of irrigated vertisols in northern New South Wales.
What did the research involve?
Fine root densities of cotton, maize, and sorghum were measured in four irrigated experiments located in two fields at the Australian Cotton Research Institute, near Narrabri in New South Wales, Australia. The experiment, which commenced in 1985, investigated the effects of combinations of tillage methods and crop rotations on soil quality and hydrology, cotton agronomy and yield, profitability and disease incidence. Root numbers in the 0.10 to 0.9 m depth was measured at 0.10 m depth intervals with a “Bartz” BTC-2 minirhizotron video camera1 and I-CAP image capture system1. The video camera was inserted into clear, plastic acrylic minirhizotron tubes (50 mm diameter) installed within each plot, 30 from the vertical.
What were the key findings?
Fine root density of cotton was low, with most occurring in the surface 0.5 m. Subsoil root number densities of cotton were very low in continuous cotton under conventional tillage and on permanent raised beds (PRBs) but were greater with a cotton-wheat rotation sown on PRBs. Averaged over the two seasons, 2004–2005 and 2006–2007, and depth intervals, there were 3.4 roots 100 mm2 in continuous cotton sown after conventional tillage, 1.2 roots 100 mm2 in continuous cotton sown on PRBs and 6.0 roots 100 mm2 in cotton-wheat sown on PRBs. Between cotton genotypes, root number density during boll production and filling of a Bollgard1-Roundup-Ready1 cotton variety was less than that of its corresponding non-Bollgard variant. Maize live root numbers did not differ significantly between continuous maize and a cotton-maize rotation but differed between depth intervals. Averaged over years and rotations, during tasselling maize had 21.5 roots 100 mm2 in the 0.1–0.5 m depth interval and 5.3 roots 100 mm2 in the 0.6–0.9 m depth interval. Root number density of sorghum was greater with no-tillage than with tillage in wetter seasons but generally similar or lower during a drier season.
Fine root density of cotton was low, whereas those of sorghum and maize were high with relatively large values occurring in the deeper subsoil. Maize and sorghum were able to tolerate the waterlogged conditions in the sodic subsoils of these vertisols and may, therefore, be more suitable rotation crops for irrigated cotton farming systems than the more commonly sown wheat.