- Agronomic: wheat
- Crop Production: cover crops, double cropping, no-till
During 2009 and 2010, on-farm testing was conducted in southwestern Oklahoma to evaluate the use of summer cover crop in a continuous winter wheat cropping system. Guar, cowpea, soybean, and mungbean were seeded in late June following wheat harvest. Cover crops were terminated after 60 days of growth. The use of cover crops did not did not decrease wheat grain yield in the following wheat crop. Data generated from the test locations indicated cowpea to be the best choice of a summer cover crop. Inclusion of a cover crop appears to help increase diversity into a monoculture wheat cropping system.
Producers in western Oklahoma have identified two main areas that they feel need to be addressed to increase the sustainability of their cropping systems: 1) lack of crop diversity and 2) reduction of N fertilizer/increase in nitrogen use efficiency.
Lack of crop diversity: Continuous monocultures are the predominant cropping systems in this region. This lack of diversity increases pest pressures and increases needs for chemical inputs, especially nitrogen fertilizer and herbicides. Dependence on inorganic inputs threatens long-term sustainability. Growers in this region also rely heavily on conventional tillage practices which do not encourage the build-up of organic matter. Ongoing economic pressure from increasing fuel and nitrogen prices provides an ideal opportunity to educate producers about the use of cover cropping systems in order to move toward long-term sustainability. A recent survey in Garfield County Oklahoma (western OK) indicated that 79% of producers would consider the use of legumes as cover crops for nitrogen savings, but lack of knowledge and information was prohibitive (Cardwell, 2007).
In areas of western Oklahoma where precipitation (< 900 mm yr-1) is the main limiting factor in dryland cropping systems the use of cover crops has generally been viewed as unacceptable due to limited precipitation. The current general consensus of many producers in the western part of Oklahoma is that no suitable summer crops exist for their climate and no suitable alternative exists to replace wheat forage for cattle, so they are reluctant to grow anything except winter wheat. Quality of winter wheat has continued to decline in this area because of increased weed and insect populations as a result of minimal crop rotation. Another aspect of limited rotation is that no-till systems have not become popular in this region because of yield reduction under no-till with continuous winter wheat. In order for Oklahoma producers to successfully implement no-till in their cropping systems they must be willing to rotate crops. One potential is through the use of cover crops, especially during the summer months when temperatures are high and rainfall is highly variable. Even if producers continue to plant winter wheat each fall, using a summer cover crop would introduce some diversity into their systems.
Reduction of N fertilizer: Nitrogen contribution from leguminous cover crops is well documented throughout the US. Use of tradition-based fertilization practices results in approximately 65% of applied nitrogen fertilizer being lost to volatilization and leaching (Johnson and Raun, 2003). We have the technology to better predict crop N needs through use of optical sensor instruments. We propose sensor-based nitrogen recommendations as a mechanism to change the farmer behavior of tradition-based fertilization practices and move towards a more sustainable system.
The sensor-based system, accurately accounts for nitrogen mineralized by biological processes and, therefore, provides nitrogen recommendations that more accurately reflect crop needs. In contrast to soil sampling and yield goals, sensor-based nitrogen recommendations allow the producer to accurately gauge the amount of N that has been mineralized through natural biological processes (http://www.soiltesting.okstate.edu/SBNRC/SBNRC.php).
Cardwell, Bart. 2007. Conservation Till 101 Attendee Survey. Enid, OK. 8 February 2007.
Johnson, G.V. and W.R. Raun. 2003. Nitrogen response index as a guide to fertilizer management. J. Plant Nutr. 26: 249-262.
The objectives of this on-farm study will be to 1) determine the effect of cover crops on grain yield of the subsequent wheat crop and 2) determine nitrogen contribution using the Green SeekerTM Optical Sensor.