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PNW CONSERVATION TILLAGE HANDBOOK SERIES
Chapter 6 - Fertility, No. 9, Winter 1987


Variable Importance of Fertilizer Placement

Roger Veseth

Fertilizer management research in conservation tillage has been an important part of the STEEP research program over the past 12 years, The placement of fertilizer in relation to the seed has been the focus of many of the projects.

Fertilizer banded below seeding depth near the seed row, for early seminal root access, has commonly increased cereal yield. However, research results have been variable under different precipitation zones, crop rotations and other factors, indicating there are other important factors influencing crop fertilizer response that need to be considered, in addition to placement.

The results of research which show the advantages of fertilizer placement have received considerable publicity, capturing the attention of farmers and the agricultural equipment industry. In the mid- 1970's there were only three commercial models of no-till grains drills available in the Northwest, none of which could deep-band fertilizer. Now, most of the 16 or more models of no-till and minimum tillage drills have deep fertilizer-placement options. Many farmers have also modified older drills, including conventional drills, for deep fertilizer banding using numerous attachments for fertilizer placement now available.

Because of the variability of research results, however, there is a concern that farmers may be spending money for drills or modifications for fertilizer placement which, in some cases, may not be needed, Most studies in the lower to intermediate precipitation areas under cereal rotations have shown that fertilizer banded below seed depth near the seed row results in higher yields than with surface broadcasting or a wide separation between the seed and the fertilizer band. In higher precipitation areas, when cereals follow legumes in rotation, yield response to fertilizer band location has been more variable.

Northern Idaho Research

A STEEP fertilizer placement study on no-till winter wheat seeded after spring peas or lentils in northern Idaho helps emphasize the fact that fertilizer placement can be overshadowed by other soil or environmental factors. Four years of experiments were conducted between 1982 and 1986 by University of Idaho agricultural engineers Charles Peterson and Edwin Dowding, and research assistants Kyle Hawley and John Whitcraft.

Five fertilizer positions were evaluated in the research: (1) surface applied (SA); (2) with the seed (WS); (3) 2 inches below the seed (BS); (4) centered between 12-inch seed rows at seed depth (CS); and (5) centered between 12-inch rows, 2 inches below seed depth (CB). A plot sized research drill used 1-inch wide shanks to place fertilizer, followed by double disk seed openers on a 12-inch spacing.

The first 2 years of the study compared nitrogen (Solution-32) at fall application rates of 40, 80 and 120 pounds/acre. Each plot was split for spring top-dress applications of O to 80 pounds/acre (16 pounds/acre increments to 80 pounds/acre) in 1983 and O to 100 pounds/acre (at 20 pounds/acre increments) in 1984. The studies were conducted at two locations near Moscow (22-inch precipitation area) and one near Reubens (24-inch).

The last 2 years compared placement of phosphorus (liquid 10-34-0) and sulfur (liquid thio-sol). Phosphorus was applied at rates of O, 20, 40 and 60 pounds/acre P205. Sulfur was applied at O, 12,24 and 36 pounds/acre S. All phosphorus and sulfur applications were made in the fall only. Trial locations were near Troy (26-inch precipitation), Cavendish (26-inch) and Reubens (24-inch).

The researchers found no consistent advantage of applying fertilizer in one position over another. The results were often site specific, varying between locations and years. Fig. 1 summarizes the yield results of the 4-year study averaged over all application rates. Compared to the other placement options, nitrogen placed below the seed had a 2 to 3 bushels/acre advantage and centered between rows; below seed depth had a 3 to 4 bushels\acre advantage. Sulfur placed with the seed reduced yields by 5 to 7 bushels/acre when compared to other placements, probably because of dry conditions at two locations in the 1984-85 crop.

Some general conclusions and trends the researchers made from the 4-year study include:

1. Fertilizer dated on the surface tended to stimulate weed production, especially wild oats.

2. A statistically significant difference in yield because of placement was not detected. However, fertilizer with the seed tended to be associated with lower overall yield.

3. Sulfur placed with the seed decreased emergence and yield at two locations when soil water content was relatively low.

4. The first 20 pounds/acre increment of phosphorus produced virtually all the yield increase observed.

5. Sulfur applications did not increase yield in the study. 6. A split fall-spring nitrogen application generally resulted in the highest yields.

Fig. 1. Summary of winter wheat yield-response to five fertilizer placement positions averaged over rates for nitrogen (1983 and 1984) at three locations, and for phosphorus and sulfur (1985 and 1986) at three locations in northern Idaho.

Recommendations

Based on the results of these studies, the researchers recommend that when a choice is available, fertilizer should be placed below the seeding depth, either below or to the side of the seed. However, major increases in yields should not be expected following legume crops in higher precipitation areas of northern Idaho. Also, since the first increments of fertilizer typically gave the largest yield increases, they suggest a conservative use of fertilizer based on soil test levels.

They stress that to obtain the most efficient use of applied fertilizer, several factors need to be considered including:

1. Soil test results — plant-available nutrient levels.

2. Fertilizer type — toxicity, mobility in soil, precipitation effect.

3. Application rate – based on soil tests and expected yield.

4. Soil temperature — affect on root growth, nutrient uptake/availability.

5. Time of application — fall vs. spring, potential loss/availability.

6. Soil water content, soil pH, soil type (texture, depth, etc.).

7. Cropping and fertilizer history.

8. Placement for root access.

These factors are interrelated so that optimizing fertilizer use includes consideration of each factor. They conclude that placement is only one facet of a complex problem and proper choice of placement must be made in the context of the total situation.

     
 

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