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In conservation tillage systems, band placement of fertilizer in the cereal root zone has commonly been reported to increase early plant growth and grain yield when compared to surface broadcast. Besides placing the fertilizer in a position more accessible for plant roots, deep banding fertilizer below the crop residue layer reduces competition for nutrients from soil microbes decomposing the residue. This is particularly important for nitrogen. In calcareous soils, banding also reduces the chemical tie-up of phosphorus into less available forms.
In 1983, a study was initiated with spring wheat to compare the efficiencies of nitrogen fertilizer use between deep-banded and broadcast treatments under both no-till and conventional tillage. This study was conducted by Bobette Parsons, soil research assistant, and Fred Koehler, soil scientist at Washington State University in Pullman.
Dirkwin spring wheat was seeded under both a conventional system with spring plowing and no-till, with a hoe drill that banded the fertilizer 2 inches below the seed. The experiment was located near Davenport, WA, in a 16-inch annual precipitation zone. Spring wheat was the previous crop in a rotation of winter wheat followed by 2 years of spring wheat. In both the banded and broadcast fertilizer treatments, 60 pound/acre PZ05 was banded 2 inches below the seed at planting time. Ammonium nitrate-sulfate (ANS) at a rate of 90 pounds/acre nitrogen and 18 pounds/acre sulfur was either banded with the phosphorus or broadcast under both tillage treatments.
Banding fertilizer had a pronounced effect on plant vigor and growth rate in both no-till and conventional tillage. This was particularly noticeable during the first 4 weeks after emergence. Wheat in broadcast treatments appeared tunted and chlorotic compared to the band treatment. At any given date during the season, the plants in the band treatment were physiologically more developed than those under the broadcast treatment in both no-till and conventional tillage. By mid-tillering, plants in the band treatments produced an average of 2 to 4 more tillers than those in the broadcast treatments, regardless of tillage system.
Fig. 1. Total nitrogen uptake In spring wheat as affected by fertilizer placement In conventional tillage, 1983 (Parsons, Koehler-WSU).
The total nitrogen uptake (fertilizer and soil N) in the above ground portion of the plants for the two fertilizer placement and tillage treatments is shown in Figs. 1 and 2. Under conventional tillage, fertilizer placement had little effect on the total nitrogen accumulation at maturity. Nitrogen uptake in the banded treatment was greatly increased over the broadcast treatment in earlier stages of crop growth, however. In contrast, deep-banded fertilizer placement in no-till increased by 36 percent the total nitrogen accumulation in the crop at harvest compared to the broadcast treatment.
A strong correlation was found between the amount of total nitrogen uptake at harvest and grain yield. Table 1 illustrates the yield increase due to banding the nitrogen, phosphorus and sulfur fertilizer below the seed compared to broadcasting the nitrogen and sulfur under both tillage systems. Compared to broadcasting, banding fertilizer resulted in yield increases of 15 percent for conventional tillage and 49 percent for no-till. This demonstrates the importance of deep fertilizer placement in no-till spring wheat under these climatic conditions.
To evaluate the efficiency of fertilizer nitrogen use, the fertilizer nitrogen taken up by the plant must be measured separately from the soil nitrogen. To accomplish this, the researchers used nitrogen fertilizer containing a special isotope of nitrogen ( 15N) that can be distinguished from non-fertilizer or soil nitrogen ( 14N). The uptake of this "labeled" fertilizer nitrogen by the spring wheat under both tillage and fertilizer placement treatments by harvest is shown in Table 2.
Fig. 2. Total nitrogen uptake in spring wheat as affected by fertilizer placement in no-till, 1883 (Parsons, Koehler-WSU).
Statistically, crop fertilizer nitrogen use between no-till and conventional tillage was no different in either the banded or broadcast treatments. A large difference was measured between the fertilizer placement treatments, however, with 45 and 46 percent increases in fertilizer nitrogen use with banding. Average fertilizer use efficiency for the banded treatments in both tillage systems was 75 percent, accumulating 65 to 69 of the 90 pounds/acre fertilizer nitrogen. In contrast, only about 40 percent of the broadcast fertilizer nitrogen was taken up by harvest. This means that as much as 60 percent of the applied fertilizer nitrogen was not taken up by the crop and would be subject to leaching and volatilization losses before the next growing season.
Fig. 3. Days after application Broadcast fertilizer nitrogen held In the surface crop residue under no-till, Davenport, WA, 1983 (Parsons, Koehler-WSU).
The labeled nitrogen (15N) was also used by Parsons and Koehler to determine the amount of broadcast fertilizer nitrogen ''tied-up" in microbial decomposition of surface residue under no-till. Yield of the previous year's spring wheat crop was about 45 bushels/acre. The residue was analyzed for fertilizer nitrogen held in both the inorganic (NH, and NO,) and organic forms. Fig. 3 shows that 14 of the 90 pounds/acre of broadcast nitrogen fertilizer (about 16 percent) was held in the residue of the previous spring wheat crop early in the season.
Within 61 days after application, most of the inorganic fertilizer nitrogen was released from the residue and moved into the soil. By harvest, 121 days after application, only about 5 of the 90 pounds/acre broadcast fertilizer nitrogen (less than 6 percent) remained in the residue, and this was in the organic form. In no-till plantings after winter wheat, the higher residue levels would probably tie-up a greater portion of broadcast fertilizer nitrogen than in this case after spring wheat.
Table 1. Spring wheat grain yield from banded and broadcast fertilizer placement in conventional tillage and no-till, Davenport, WA, 1983 (Parsons, Koehler-WSU).
Table 2. Spring wheat uptake of 90 pounds/acre fertilizer nitrogen by harvest under banded and broadcast treatments in conventional tillage and no-till, Davenport, WA, 1983 (Parsons, Koehler-WSU).
us: Hans Kok, (208)885-5971
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