2007 - Maximizing Irrigated Crop Yields in the Great Plains
2006 - Maximizing Irrigated Crop Yields in the Great Plains
2005 - Maximizing Irrigated Crop Yields in the Great Plains
2004 - Maximizing irrigated crop yields in the Great Plains
2003 - Maximizing Irrigated Corn Yields in the Great Plains
2002 - Maximizing Irrigated Corn Yields in the Great Plains
2001 - Maximizing Irrigated Corn Yields in the Great Plains
2000 - Maximizing Irrigated Corn Yields in the Great Plains
Maximizing Irrigated Crop Yields in the Great Plains, 2007
Several years of irrigated field research in north central Kansas clearly demonstrated the importance of complete and balanced nutrition in the production of high-yield corn. However, fertilization of soybeans in a common corn/soybean rotation has traditionally been secondary to corn fertilization, as the crop is usually left to scavenge nutrients remaining after corn. This study was started in 2004 as an expansion of the original corn research to determine the benefit of direct fertilizer application to sprinkler-irrigated soybeans.
Treatments in this study were row spacing (30 in. and 7.5 in.), plant population (150,000 and 225,000 plants/A), and seven fertility treatments. The N, P, and K fertility treatments consisted of a low P application, low P-low K, low P-high K, high P-high K, NPK, and an unfertilized check. Phosphorus application rates were 30 (low) or 80 (high) lb P2O5/A, and K treatments were 80 (low) or 120 lb (high) K2O/A. The NPK treatment consisted of 20-80-120 lb N-P2O5-K2O/A. In 2005, manganese (Mn) at 5 lb Mn/A was applied along with the NPK treatment to evaluate the effect of Mn on glyphosate-ready soybeans. Initial (2004) soil test values were: pH 6.5; 23 ppm Bray-1 P (very high); and 236 ppm exchangeable K (very high). All fertilizer was broadcast in mid-March.
Soybean yield has not been affected by row spacing or plant population in any year of this study. However, fertilization has had a significant impact on soybean yield every year. In the first 2 years, the high P-low K treatment produced a maximum yield increase over the unfertilized check, with a 2 year average increase of 33 bu/A. Applying additional K or adding N did not increase yields over the high P-low K treatment. Adding Mn to the NPK treatment increased yield by 5 bu/A in 2005. However, in 2006 yield was maximized by the low P rate, with additional P, K, and Mn showing no advantage. The low P rate in 2006 increased yield by about 30 bu/A over the unfertilized control. In 2007, the low P and K rates increased yield over the control by 33 bu/A, from 49 to 82 bu/A. The maximum yield response in 2007 was with the complete N-P-K-Mn treatment where yield was 90 bu/A...41 bu higher than the zero fertilizer check. The addition of Mn resulted in a 5 bu/A yield increase and N fertilization provided no yield advantage in 2007. This work has demonstrated the importance of direct fertilization of soybeans in high-yield environments. It has continued for 4 years with relatively consistent results and will not be continued in 2008. KS-33F