Strip-tilling and deep-banding nitrogen and phosphate increased corn grain yield versus conventional tillage and conventional fertilizer placement methods in highly erodible, low-fertility soils in 2007 research at the USDA’s Agricultural Research Service Northwest Irrigation & Soils Research Laboratory at Kimberly, Idaho.

The effects of tillage, nitrogen and phosphate placement on grain and biomass yield of field corn were assessed on two sites with different levels of soil fertility and productivity.

The sites were selected in a furrow-irrigated field that had been cropped to alfalfa. Site A was located in the top half of the field and Site B was located in the bottom half of the field. Site A had lower levels of soil organic carbon and soil test phosphorus and potassium than Site B. The treatments were:

1. Strip-till with deep placement of nitrogen and broadcast phosphate
2. Strip-till with 2-by-2-inch placement of nitrogen and broadcast phosphate
3. Strip-till with deep placement of nitrogen and phosphate
4. Conventional tillage with 2-by-2-inch placement of nitrogen and broadcast phosphate
5. Conventional tillage with broadcast nitrogen and phosphate.

The grain yields at Site A were greater for strip-till compared to conventional tillage. The deep-band placement of nitrogen and phosphate with strip-till yielded 175 bushels per acre — an advantage of 23 and 16 bushels per acre over both conventional-tillage treatments.

Yields at Site A from deep-banding phosphate and potash were similar to those in Site B, which averaged 178 bushels per acre. There were no differences in grain yield at Site B for all treatments.

Soil Fertility

In 2007, prior to field operations, 20 soil subsamples were collected at depths of 0 to 12 and 12 to 24 inches across all replications for both Site A and Site B. Rates of 105 pounds of nitrogen per acre and 58 pounds of phosphate per acre were applied to the treatments as urea (46-0-0) and mono-ammonium phosphate (11-52-0).

A credit of 60 pounds of nitrogen per acre from alfalfa was applied. All treatments were replicated four times in a randomized complete-block design. Fertilizers were either broadcast prior to tillage, or placed 2-by-2-inch at planting or placed 7 inches below the soil surface and directly below the seed during strip-till.

Chisel-tillage treatments consisted of chisel plowing and tandem discing on May 11 and roller-harrowing May 16. The broadcast application of urea on May 16 to Treatment 5 was immediately incorporated with the roller-harrow. Strip-tillage occurred on May 23. Pioneer Hi-Bred’s 3523 — which has a growing-degree-day maturity of 2,530 — was planted to the entire study area on May 24 at a rate of 31,000 seeds per acre.

Soil organic carbon, soil-test phosphorus and soil-test potassium in the 0-to-12-inch and 12-to-24-inch depth were lower at Site A than Site B.

At Site A, soil-test phosphorus in the top 12 inches was considered low to marginal according to the University of Idaho fertilizer recommendations for field corn. The recommendations suggested applications of 20 to 140 pounds of phosphate per acre, depending on the soil lime content. The soil test potassium at Site A suggested no additional potash was needed.

Grain Yield

There were significant differences in grain yields between treatments at Site A. Treatment 3 (strip-till and deep placement of nitrogen and phosphate) at Site A had greater grain yields than both the conventional-tillage treatments.

Treatment 3 grain yields were 23 and 16 bushels per acre greater than Treatment 4 (conventional-tillage, 2-by-2 placement of nitrogen and broadcast phosphate) and Treatment 5 (conventional tillage and broadcast nitrogen and phosphate), respectively.

A direct comparison of tillage effects on grain yield could be made between Treatment 2 (strip-till, 2-by-2 placement of nitrogen and broadcast phosphate) and Treatment 4 (conventional tillage, 2-by-2 placement of nitrogen and broadcast phosphate). Strip-tillage yielded 14 bushels per acre of corn more than conventional tillage.

Averaged over all treatments, the grain yield at Sites A and B were 164 bushels per acre and 178 bushels per acre, respectively.

Unlike site A, there were no grain yield differences between treatments at Site B. The response of grain yield to tillage and nutrient placement at Site A was likely a result of the overall lower fertility associated with furrow-irrigated-induced soil, organic carbon and nutrient transport.

The impact of tillage and nutrient placement was negligible at Site B due to an overall greater level of fertility, a result of soil organic carbon and nutrient deposition from Site A.

These results from the first year of study indicate that corn grown in areas of fields with shallower soil depths, low in organic carbon and nutrients due to erosion and other factors, may have a greater yield response to strip-till and deep placement of nitrogen and phosphate compared to conventional tillage and conventional fertilizer placements.