Tillage, Planting Date, and Plant Population Effects on Dryland Corn

Dryland corn (Zea mays L.) usually is not grown in western Kansas because of its low yield potential under drought stress. A study was conducted at the Southwest Research-Extension Center near Garden City, KS, from 1991 through 1994 to determine proper management practices for dryland corn. Corn was planted in a wheat (Triticum aestivum L.)-corn-fallow rotation in early (D1), mid (D2), and late (D3) May at plant populations of 12 000 (P1), 18 000 (P2), and 24 000 (P3) plantdacre with conventional tillage (CT) and no tillage (NT). No tillage increased yields 100% in the driest year (1991), increased yields by 41% in 1994, and resulted in yield increases in most comparisons in the remaining years. The highest yields in the dry year of 1991 resulted from D1 and D3, whereas D1 and D2 usually produced the highest yields in all other years. In 1991, yields declined with increased plant population, but the average yield reduction of 16% for P3 with NT was half that with CT. In other years, yields usually increased with an increase in population. In 1992 and 1993, P3 resulted in average yield increases,over P1 of 41% and 28% with NT and CT, respectively. In 1994, NT usually produced the most grain with P2, whereas population increases did not increase CT yields. We conclude that dryland corn in southwest Kansas should be planted in early to mid-May at plant populations not exceeding 18 000 plants/acre. No tillage is essential for adequate yields in dry years and will usually result in yield increases in years with more favorable climatic conditions. Research QuestionDryland corn is grown on a limited acreage in the western Great Plains and is most common in western Nebraska, with fewer acres in western Kansas and eastern Colorado. Most acres in western Kansas are in the northern portion of the area and decline from north to south because of the susceptibility of corn to high temperatures and evaporation. Dryland corn acreage has increased in northwest Kansas from about 1000 acres in 1980 to 71 000 acres in 1993. Acreage in southwest Kansas has averaged only 1000 acres since 1980, but about 13 000 acres were harvested in 1985 and 1993. Producers are encouraged by yields in a wet year, plant more acres in the following year, often have yields reduced by dry weather, and then reduce their acreage. Part of the reason for inconsistent yields is that relatively little research has been done on management practices for dryland corn, particularly in areas south of Nebraska. Most other research on nonirrigated corn has been conducted in the midwest. The objective of this study was to determine proper management practices for dryland corn in southwest Kansas with respect to tillage, planting date, and plant population. Literature SummaryImportant management practices in all corn-growing areas are tillage, planting date, and plant population. In the Corn Belt, corn typically is planted in late April through early May at 25 000 to 30 000 plants/acre. In western Nebraska and northwest Kansas, dryland corn also is planted in late April through early to mid-May, but at reduced populations of 8 000 to 15 000 plants/acre to reduce drought stress. No tillage (NT) sometimes reduces yield in the northern areas of the Corn Belt, because of wet conditions, but NT typically increases yield in the Great Plains. Study DescriptionThe study was conducted at the Southwest Research-Extension Center near Garden City, KS, from 1991 through 1994. The soil type was a Ulysses silt loam having a pH of 7.8 and an organic matter content of 1.5%. Long-term climatic data for Garden City are: precipitation, 17.91 in.; mean temperature, 53.2F; open pan evaporation (April–September), 71.19 in.; and frost-free period 170 d. Corn was planted in the wheat-corn-fallow system in early, mid, and late May at 12 000, 18 000, and 24 000 plants/acre. Conventional (sweep) tillage (CT) and NT were compared. Applied QuestionsWhat effects did the management practices tillage, planting date, and plant population have on dryland corn? No tillage generally increased yield in all years, with the most dramatic effects occurring in the dry year of 1991, when NT yields were twice those of CT, and in 1994, when yields were increased by 41% (Table 1). In 1991, the highest yields resulted from the first and last planting dates. Heat stress at pollination caused the reduction in yield from the second planting date, whereas rainfall in late August benefited corn planted on the last planting date. In the other years, planting dates of early to mid-May usually produced the highest yields. An increase in plant population resulted in decreased yields in 1991 but usually increased yields in the other years. What are the best planting date, plant population, and tillage practices for dryland corn? The optimum planting date for each year cannot be predicted, because stress can occur during critical growth stages following any planting date. The first two planting dates usually produced the most grain, however. A yield increase with NT occurred in all years, and although a yield decrease occurred at 18 000 plants/acre in the driest year, yield was usually higher at this population in the other years, particularly with NT. The yield from 24 000 plants/acre was consistently higher than that from 18 000 plants/acre only in the cool, wet year of 1992, and yielded no better than 18 000 plants/acre in 1994, even with NT. Therefore, dryland corn in southwest Kansas should be planted in early to mid May at a population not exceeding 18 000 plants/acre. No tillage is essential, that adequate yields can be produced in a dry year. Table 1Effects of tillage, planting date, and plant population on dry-land corn yield. TillagePlanting datePlant populationYearCT†NTD1D2D3P1P2P3-----------------------------bu/acre-----------------------------199120403124333329261992134137146144117113138155199388969397867996101199473102909280829189†CT = Conventional tillage, NT = No tillage; D1, D2, D3 = Planted in early, mid, late May, respectively (D3 was 11 June 1992); P1, P2, P3 = 12 000, 18 000, 24 000 plants/acre, respectively (11 000, 13 000, 18 000 in 1991).