An Agronomic and Economic Comparison of the Wheat-Corn-Fallow and Wheat-Sorghum-Fallow Rotations

Winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] in the central and southern Great Plains are often grown in a 3-yr wheat-sorghum-fallow (WSF) rotation. Corn (Zea mays L.) can be substituted for sorghum in northern areas but is believed to lack sufficient drought and heat tolerance for southwest Kansas and areas further south. However, interest in dryland corn is increasing. We conducted a study from 1992 through 1995 near Garden City, KS, to compare wheat-corn-fallow (WCF) and WSF. Four tillage systems were compared: all conventional tillage (CT); all reduced tillage (RT); all no-tillage (NT); and a CT wheat, NT corn or sorghum combination (CNT). Wheat yields were unaffected by rotation and tillage. Corn yielded more than sorghum in 12 of 16 tillage × year combinations, primarily due to above average precipitation. Corn yields were increased by RT and NT in 3 of 4 yr whereas they increased sorghum yields in only 1 yr. Average returns from WCF were $31.22/acre per yr, whereas those from WSF were $19.79/acre per yr. Returns of WCF exceeded WSF returns in 10 of 16 tillage × year combinations. Average income for CNT in WCF exceeded incomes from CT, RT, and NT by $6, $7.16, and %11.9O/acre per yr, respectively. The CNT system in WSF produced %3.79/acre per yr more than RT and %6.14/acre per yr more than NT, but $5.84/acre per yr less than CT. Under the conditions of this study, WCF was superior to WSF in terms of yield and return. The CNT system usually produced more return, particularly in WCF. Research QuestionThe dryland 3-yr wheat-sorghum-fallow (WSF) rotation has proven superior to the 2-yr wheat-fallow (WF) rotation in terms of yield and profits in the central and southern Great Plains. A natural progression from WSF is wheat-corn-fallow (WCF). Corn has a higher yield potential than grain sorghum, but may not have enough heat and drought tolerance for adequate grain production in southern areas of the region. Therefore, a study was conducted to compare WCF and WSF, with objectives of: (i) determining which rotation produces the highest yields and profits, and (ii) determining whether a conventional-till (CT) wheat, no-till (NT) corn or sorghum system is more profitable than all reduced-till (RT) or NT systems. Literature SummaryWheat-fallow is the most common dryland cropping system in the Great Plains and produces a crop every other year. Wheat-sorghum-fallow produces two crops in 3 yr and results in more grain and profit than WF, particularly when combined with RT or NT. Success with WSF is due to efficient use of precipitation and stored soil water by grain sorghum produced in RT or NT systems. Grain sorghum has responded to RT and NT more consistently than wheat. Because CT wheat is cheaper to produce than RT or NT wheat, a CT wheat, NT row-crop system should reduce expenses compared with an all-NT system and produce more grain than an all-CT system. The WCF rotation has been successful in the northern areas of the central Great Plains but has not been practiced on significant acreage south of northwest Kansas. Study DescriptionThe study was conducted at the Southwest Research-Extension Center near Garden City, KS, from 1992 through 1995. Long-term climatic data for Garden City are: precipitation, 17.91 in.; mean temperature 53.2°F; open-pan evaporation (April–September) 67 in.; and fiost-fiee period, 169 d (26 April–12 October). The WCF and WSF rotations were compared using all CT, all RT, all NT, and a CT wheat-NT corn or sorghum system (CNT). Populations for corn ranged from 12 700 plants/acre in 1992 to 16 700 plants/acre in 1995, whereas the population for grain sorghum averaged about 25 000 plants/acre. The wheat seeding rate was 60 lb/acre. Applied QuestionsWhat were the differences in the two rotations? The cost of production, yield, and returns of wheat were not affected by rotation. The biggest difference in cost between corn and sorghum was seed cost, with corn seed costing more than seven times higher than sorghum. Corn herbicides and insecticides were slightly more expensive. Corn was planted earlier than sorghum and required one less tillage operation in CT. The number of spray operations in RT and NT were the same in WCF and WSF. What were the results of the study? Corn yields ranged between 78 and 128 bu/acre, whereas sorghum yields ranged between 42 and 101 bu/acre. Because of favorable climatic conditions, corn yielded more than sorghum in 12 of 16 tillage × year comparisons, with the yield increases more than compensating for higher production costs. Corn responded more to RT and NT than did sorghum, making WCF more profitable than WSF as tillage was reduced. Returns in WCF ranged from $25.59/acre per yr for NT to $37.49/acre per yr for CNT. Returns in WSF ranged from $14.67/acre per yr for NT to $26.65/acre per yr for CT. Returns were higher for CNT than for NT in WCF because wheat did not respond to a reduction in tillage and herbicide expense was less in the wheat phase of the rotation. Retums were highest for CT in WSF because sorghum did not respond to a reduction in tillage as in previous studies. RecommendationsThe results of this study indicate that WCF was more profitable than WSF. However, the study was conducted under climatic conditions more favorable than can be expected every year. The results do illustrate the high yield potential of corn. At this time, the recommendation is for a farmer to plant corn on a relatively small number of acres. Over a long time, we feel that high corn yields in favorable years will more than compensate for low corn yields in less favorable years. If fbture research and experiences of producers confirms this, dryland corn acreage in the more arid areas of the Great Plains will increase.