Maximizing winter wheat production with conservation tillage in the Northern Great Plains

Project assessing the potential for reduced tillage production of winter wheat in the Northern Great Plains


13 Jun 2001


    Cultural practices have rarely been developed in which consideration has been made for varietal differences. This is due in part to the traditional crop-fallow system of small grain production in the Northern Great Plains. The advent of conservation tillage has provided a need for tillage-variety interaction research. In the Palouse region of eastern Washington, Siha found that the yield and test weight of four spring wheat varieties depended upon variety and tillage (conventional vs notill) variables. Different production response by varieties may also be the result of nutrient efficiency, water efficiency, seeding rate, row spacing, and drought tolerance.

    In 1983 three varieties of winter wheat were grown in conjunction with several levels of nitrogen. All varieties yielding about 40 bu/a; however, the nitrogen efficiency of the varieties ranged from 2.5 lb N/bu/a to 4.0 lb N/bu/a. Current N fertilizer recommendations provide for 2.6 lb N/bu/a. Obviously winter wheat varieties are not equally efficient users of nutrients. These data obtained by Dubbs at the Central Agricultural Research Center, Moccasin, MT were from a crop-fallow rotation. It is likely that these differences will increase if tillage investigations into variety-production interactions on conservation tillage are not conducted.

    Nutrients also play an important role in maintaining good plant-water relations which contributes to kernel plumpness and protein. Nitrogen is especially important to protein but there is evidence to indicate that low nitrogen levels decrease yield.

    All small grains in semiarid regions usually undergo water stress at some time during the summer growing season. Plants can respond to this stress by accumulating nutrients in the plant. The ability of a plant to respond is thought to be partially variety dependent.

    Research is currently being conducted at the Western Triangle Research Center on osmoconditioning of winter wheat varieties in relation to winterhardiness criteria. Preliminary results indicate that varieties have inherently different abilities to adjust to low temperatures by accumulating nutrients in the plant magnitude of adjustment is also affected by tillage management. Some researchers have speculated that osmoconditioning may also be a drought tolerance mechanism.

    The ability of a specific variety to tolerate drought and mild water stress is also related to the pattern of root growth and water extraction from the sol throughout the growing season. Field studies at the Western Triangle Research Center during 1984 on water use extraction and rooting patterns of spring wheat and barley illustrated substantially different results among varieties. Water use was similar within a crop but rooting depths ranged from approximately 1.5 to 6 ft by midseason. Most varieties were more deeply rooted in the no-till than in the summer fallow.

    Predictions of winter wheat production are based upon plant available water which includes stored soil moisture and growing season precipitation. In general, 4 inches of moisture are required to establish the crops; each additional inch of moisture used by the crop will produce 7 bu/a of grain under good management. This level of water use efficiency may be increased through proper variety selection for specific tillage and cultural practices.

    Another aspect of production on conservation tillage acreage is seeding. Row spacing and seeding rates may need to be altered for maximum production in light of a different growing environment. A four year study in the Palouse resulted in increased yields with increased seeding rates from 0.66 to 1.25 bu/a for 2 of 5 barley varieties, 1 of 3 oat varieties, and 1 of 5 spring wheat varieties. Variation in row spacing from traditional 10 to 14 inch spacing in semiarid regions may also improve production based on research by Krall in Montana from the 1950's through the 1970's in which row spacing in excess of 14 inches provided maximum yields on summer fallow.

    These data and other research on conservation tillage support the need and indicate the importance of examining winter wheat varieties under various conservation tillage practices to fully utilize variety-production interactions in order to maximize yields.