Soil fertility and soil productivity are variable within farm fields. Over or under application of a nutrient in parts of every field can result from conventional fertilizer application. This study was conducted to determine whether yield and net returns could be increased by considering field variability when applying fertilizer. The influence of soil fertility variation was considered with soil sampling on a grid pattern and with detailed soil maps made of each field. The fields, located in eastern North Dakota, were mainly a mixture of Haploborols, Calciaquolls, and Argialbolls. Wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) were grown. In 1989, variable rate fertilization based on grid soil sampling did not result in a greater yield of barley (32.1 bu/acre) than the conventional method (30.0 bu/acre). In 1990, the variable rate application yielded more barley (73.7 bu/acre) than the conventional method (67.7 bu/acre). The conventional method, however, resulted in the greatest net returns in both experiments. In 1991, the variable rate method based on a 50‐ft soil sampling grid yielded more wheat (37.3 bu/acre) than the method based on soil mapping units (33.8 bu/acre). The greatest net return ($114/acre) was obtained by using the average soil test by map unit and a yield goal of 50 bu/acre. Yields of barley and wheat were increased by consideration of soil nutrient variability but the increased cost of grid soil sampling resulted in less net return than conventional fertilization and sampling methods.
Research Question
It is well known that fertility levels often vary widely within a field due to management, soil, and other factors. This study examines the feasibility of taking soil variability into consideration to increase small grain yield in the northern Great Plains.
Literature Summary
Several recent studies indicate that yield and fertilizer use efficiency may be increased by adjusting fertilizer inputs based on soil and fertility spatial variability. The popular literature presents many hypothetical situations where variable fertilizer application should increase or maintain yield while using the same amount, or a smaller amount, of fertilizer.
Study Description
Three trials were conducted on production fields in eastern North Dakota from 1989 to 1991. The soils used developed from till in a sub‐humid climate. Five to nine soil map units were present in each field. All soils were very high in K and medium to high in P. Nitrate‐N in the top 2 ft of soil varied from 20 to over 200 lb/acre at planting time. In all years, growing season rainfall was adequate to very good. The crops grown were ‘Robust’ barley (1989 and 1990) and ‘Grandin’ hard red spring wheat (1991). Treatments in 1989 and 1990 were:
Control (no N fertilizer applied).
Conventional method (composite soil sample and a field yield goal).
Variable method (soil sample on a 50‐ft grid and a field yield goal).
Variable method (grid soil sample on a 50‐ft grid and estimated productivity of each soil map unit).
In 1991, treatments c...
Synopsis
Placement of fertilizers in polyethylene capsules effectively controlled the rate of release of the fertilizer constituents for corn and Kentucky bluegrass in the field, but did not significantly increase yield or recovery of the constituents. In the greenhouse, significant increases in recovery of N were obtained by corn for (NH4)2SO4 coated with wax and pelleted, but yields were not significantly affected.
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