Corn Root Development in Conservation Tillage Systems with Varying P&K Rates.

The objective of this study is to determine the influence of tillage, phosphorus (P) and potassium (K) placement and rate on corn grain yield, root development, and in-season soil P and K and water status.  Experiment arrangement is a split-split-block design with three replications in a corn-soybean rotation. Tillage/placement— NT broadcast (NT-BC), NT deep placement at 15 cm (NT-DP), and ST deep placement (ST-DP)— as the main plot, P rate (0, 28, 45,  and 50 kg P₂O₅ hectare^-1 year^-1) as the subplot, and K rate (0, 50, 100 and 200 kg K₂O hectare^-1 year^-1) as the sub-subplot.  Corn root samples, soil samples, and soil water measurements were collected at 0-5 cm, 5-10 cm, 10-20 cm, and 20-40 cm depth increments in the crop row (CR) and between the rows (BR) at V12 and R2 development stages in 2007 and 2008.  Mean grain yield in 2008 was 4,620 kg hectare^-1 greater than 2007. The lack of disturbance with NTBC in 2007 produced the greatest yield likely because it protected soil water loss during a dry early season. In 2008, ST-DP produced the greatest yield likely because this tillage helped warm up and dry the seedbed sooner than the no-till systems during a wet spring.  Root length density (RLD) was greater in 2007. However, in 2008 a larger mean root diameter produced greater surface area density (RSAD) than 2007 at all sampling depths.  RLD and RSAD decreased with increasing soil depth and were greatest in the surface 0-5cm in the CR than the BR position in both years. Soil water was greatest at the CR position. Compared to broadcast applications, deep banding decreased surface P and K levels but increased these levels at the 10-20 cm depth. This decrease in surface P concentrations could be important in reducing potential P surface runoff.