Fertility Management for No-till and Minimum Tillage Systems

Chapter 6 – Fertility, No. 1, August-September 1984

Roger Veseth

Changing from a conventional to a no-till or minimum tillage cropping system requires several important changes in management practices. One very important area is soil fertility management, which is greatly affected by the new plant-soil environments. Many STEEP researchers in Oregon, Washington and Idaho are working to adapt fertility management practices to these new cropping systems. One of the researchers is Fred Koehler, Washington State University soil scientist. Koehler has been evaluating fertilizer management practices for no-till and minimum tillage systems through several long-term field studies in eastern Washington. He is evaluating these practices for spring wheat and winter wheat under different crop rotations and climatic conditions.

Under conservation tillage systems most or all of the crop residue is left on the surface. This reduces at least temporarily the rate and amount of plant nutrients released through residue decomposition. If fertilizer is surface applied, it will be readily available to soil microbes that are decomposing the residue. Since microbes are generally more efficient in obtaining nutrients than crops, surface-applied fertilizer nutrients may be less available to the crop than fertilizer banded below the residue layer. Also, fertilizer broadcast on the surface is more available to weeds than if it were banded near the roots of the crop plants.

Soil temperature differences between conventional and no-till systems is another factor that influences fertilizer practices. Koehler has found that, under no-till, the upper few inches of soil below the surface residue are often 2° to 5°F cooler in the early spring than with conventional tillage. Soil phosphorus is known to be less available to plants under cooler conditions. Therefore, there may be a greater need for phosphorus fertilizer under no-till than conventional tillage. Cooler soil temperatures also reduce the rate of microbial decomposition of soil organic matter. Reduced decomposition means that less nitrogen, sulfur and other nutrients would be available to the crop from this source.

Phosphorus is largely immobile in the soil, while nitrogen in the nitrate form moves readily with the soil water. When the upper few inches of soil dry out early in the season, surface- or shallow-placed applications of phosphorus fertilizer in no-till would not be as available to the crop as fertilizer banded below the seed in the root zone.

The results of a 6-year study on fertilizer placement by Koehler near Davenport, WA, are shown in Table 1. This is a 16-inch average annual precipitation area where wheat fallow is the typical rotation. An alternating winter wheat spring wheat annual cropping system was used in the experiment since 1978, comparing the response to fertilizer placement under conventional tillage and no-till systems.

For winter wheat, the yield increase for banded fertilizer placement over broadcast averaged 5 bushels per acre under both the conventional and no-till systems. The largest winter wheat yield increase due to banding occurred in 1981 with increases of 8 bushels per acre for conventional tillage and 14 bushels per acre for no-till.

The yield advantage with banded fertilizer placement was typically greater for spring wheat than for winter wheat. Spring wheat yield increases with fertilizer banding averaged 11 bushels per acre for conventional tillage and 12 bushels per acre for no-till.

Another fertilizer placement study by Koehler is under way near Colton, WA, in a 20-inch precipitation area where annual cropping is normally used. Table 2 shows the response of no-till winter wheat and spring wheat to band fertilizer placement compared to broadcast. Yield increases with band fertilizer placement averaged 11 bushels per acre for spring wheat and 4 bushels per acre for winter wheat. This illustrates a commonly reported difference in response to fertilizer placement between the two crops.

Soil scientists Paul Rasmussen and Robert Ramig, agricultural engineer Dale Wilkins and other USDA-ARS researchers at the Columbia Plateau Conservation Research Center near Pendleton, OR, are also part of the STEEP research effort to develop fertility management practices for conservation tillage systems. Numerous experiments have been conducted in northeastern Oregon on reduced tillage and no-till management practices. Table 3 shows a comparison of winter wheat response to nitrogen under no-till annual cropping after spring wheat and conventional tillage after fallow in 1982 at the Pendleton Research Center.

Table 1. Effect of nitrogen and sulfur fertilizer placement on yield of wheat, Davenport, Lincoln County, WA.

In this experiment, grain yields without N fertilization were 38 bushels per acre for conventional tillage wheat/ fallow and 20 bushels per acre for no-till annual cropping. The higher yield in the wheat/fallow rotation was expected since it had the advantage of 2 years of mineralization of native soil nitrogen rather than 1 year in annual cropping. Grain yield increased substantially with the application of 40 and 80 pounds of N per acre.

Nearly identical increases of 37 and 38 bushels per acre were obtained from conventional wheat/fallow and no-till annual cropping, respectively, when 80 pounds of N per acre were applied. Grain yield increased nearly 0.5 bushels per acre for each pound of N applied, or conversely, 2.1 pounds of N per acre increased yield 1 bushel in both cropping systems. N response likely would not have been the same had it been broadcast in no-till seeding because of N immobilization by surface residue. These results indicate that winter wheat can use N just as efficiently in notill as in conventional tillage if the fertilizer is properly placed to avoid “tie-up” by residue-decomposing microorganisms.

At the 80-pound-per-acre N rate, grain yield under annual cropping was 58 bushels per acre compared to 75 bushels per acre in the wheat/fallow experiment (Table 3). The 23 percent lower yield in annual cropping was probably not caused by lower stored water because the soil profile in both systems was essentially full of water when spring growth started. It is more likely that 80 pounds of N per acre was not adequate for maximum yield under annual cropping or that recropped cereal grain was adversely affected by soil-borne diseases that are eliminated by fallowing. Long-term yields at Pendleton in annually cropped winter wheat are about 70 percent of yields in a winter wheat/fallow rotation, where both receive 80 pounds of N per acre.

Winter wheat grown in no-till annual cropping produced substantially less straw than wheat grown with conventional tillage after fallow (Table 3). When 80 pounds of N per acre were applied, the straw-to-grain ratio was 1.16 for the no-till seeded annual crop compared to 1.64 for conventionally tilled wheat after fallow. This difference in straw-to-grain ratio is consistent with previous research on no-till cropping; less straw is produced and the ratio is about 25 percent lower than for conventionally tilled winter wheat.

The Pendleton researchers have also noted a difference in response to band fertilizer between spring wheat and winter wheat. In general, they have found that under conservation tillage systems, banding nitrogen, phosphorus and sulfur fertilizer has consistently produced higher yields than broadcasting in spring wheat. This has not always been true in winter wheat. This difference in response may be due, in part, to the greater need for phosphorus in spring wheat with its limited root system during early spring.

Location of fertilizer bands near the seed is necessary for maximum response in spring cereals. In a fertilizer band placement study, growth of spring wheat near the end of tillering was 31 percent less when plants were located 3 inches laterally from the fertilizer band than when they are over the band. At a 7-inch separation, a 61 percent reduction in growth was measured.

From research with a modified John Deere HZ deep furrow opener, a vertical separation of 1.5 inches is suggested as minimum between seed and fertilizer where rates of N over 100 pounds per acre are applied with sulfur. When aqua-ammonia or anhydrous-ammonia are used as the primary N source, the amount of N that can be applied with a 1.5-inch separation may be lessor the seed fertilizer separation should be wide.

Table 2. Influence of nitrogen and sulfur fertilizer placement on wheat yields, Colton, WA.

Table 3. Stevens winter wheat responses to nitrogen fertilization in no-till annual cropping compared to conventional tillage after fallow.

Source: From Rasmussen, Oregon State University, Agricultural Experiment Station Special Report 680, 1983.