Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2007
Publication Date: 3/12/2007
Citation: Lyon, D.J., Nielsen, D.C., Felter, D.G., Burgener, P.A. 2007. Choice of Summer Fallow Replacement Crops Impacts Subsequent Winter Wheat. Agronomy Journal 99:578-584. Interpretive Summary: Winter wheat is the foundation of dryland cropping systems in the Central Great Plains. Summer fallow, the practice of controlling all plant growth during the non-crop season, is used to stabilize winter wheat production by storing water in the soil prior to seeding. Summer fallow stores less than 40% of the precipitation that falls during the fallow period, it produces no direct income, and it contributes to soil degradation. A short duration summer crop could be used to replace summer fallow when adequate soil water is available in the spring. The objective of this study was to ascertain the effect of four summer crops that could be used to replace fallow on the subsequent winter wheat crop. In a previous study, four short duration summer crops (dry pea, spring triticale, proso millet, and foxtail millet) were planted into soil with various beginning soil water levels created with supplemental irrigation prior to planting. In the fall of 2004 and 2005, winter wheat was seeded across these previous treatments at Sidney, NE and Akron, CO. Soil water at winter wheat seeding was greatest in plots that had a full soil water profile at the time of summer crop planting. Evidently, the short duration summer crops did not use all the soil water in these high water treatments, which left it to be used by the subsequent winter wheat crop. Soil water at winter wheat seeding was greater following dry pea and spring triticale, which were planted in early April, than after the millets, which were planted in early June. Within a given planting date, soil water at winter wheat seeding was greater following spring triticale and foxtail millet, which were harvested for forage, than after dry pea or proso millet, which were harvested for grain. This study suggests that a flexible summer fallow cropping system in which the decision to plant a summer crop or to fallow is based on stored soil water in the spring may be feasible for the Central Great Plains. Determining a threshold soil water level at which to plant a summer fallow replacement crop will be critical to the success of the system since it will not only influence the performance of the summer crop but also that of the subsequent winter wheat crop. The flexible summer fallow cropping system appears to be most applicable when using short-duration summer annual forage crops, such as triticale and foxtail millet. Forage yield is more readily estimated by soil water at planting than is grain yield and the shorter duration of forage compared to grain crops tends to leave more soil water for the subsequent winter wheat crop. However, grain crops such as proso millet, with low seed cost and a relatively good grain price, may also be feasible if a grower is willing to accept a greater variability in economic return, i.e., greater risk.
Technical Abstract: Winter wheat (Triticum aestivum L.) is the foundation of dryland cropping systems in the central Great Plains. The objective of this study was to quantify the effects of four short-season spring-planted crops used to replace summer fallow on the subsequent winter wheat crop. Wheat was seeded into four crop stubbles [spring triticale (X Triticosecale rimpaui Wittm.), dry pea (Pisum sativum L.), foxtail millet (Setaria italica L. Beauv.), and proso millet (Panicum miliaceum L.)] at sites near Akron, CO and Sidney, NE in the fall of 2004 and 2005. These summer fallow replacement crops were planted into silt loam soils at three different soil water levels at planting (low, medium, and high). Winter wheat water use and grain yield were 3.6 cm and 662 kg ha-1 greater, respectively, in the high water treatment compared to the low water treatment averaged across at all sites and years. Winter wheat used an average of 4.3 cm more water following early-planted summer crops (triticale and dry pea) than after late-planted summer crops (foxtail and proso millet), but this increased water use did not consistently translate into increased grain yield as a result of terminal drought at Sidney in 2006. No negative mean annualized net returns were observed in the high water treatments. The high cost of pea seed ($3.30 kg-1) strongly reduced profitability. The flexible summer fallow cropping system appears to be most applicable when using short-duration summer annual forage crops, such as triticale and foxtail millet.