Deep Banding Fertilizer: A Weed Management Tool!

Chapter 5 – Weed Control, No. 4, April-May 1985

Roger Veseth

The advantages of deep banding fertilizer over surface broadcast in conservation tillage systems has been well documented in the intermediate and lower precipitation zones of the Pacific Northwest. The advantages are in terms of a higher yield potential with increased early plant vigor and growth rate, and a higher fertilizer use efficiency. Placement of the fertilizer below the seeding depth and near the seed row allows the cereal’s seminal roots, which develop at the seed, early access to the fertilizer. Deep banding fertilizer near the seed row also reduces weed levels and increases the crop’s competitive advantage over the weeds.

Several STEEP research projects over the past few years have looked at the effect of fertilizer placement on grass weed populations and growth. A 2-year study in 1980 and 1981 evaluated the response of wild oats and spring wheat to nitrogen fertilizer placement. Spring wheat was no-till seeded into winter wheat stubble near Pullman, WA. The research was conducted by STEEP researchers Verlan Cochran and Larry Morrow, soil scientist and research agronomist with the USDA-Agricultural Research Service at Pullman, and Margaret Reinertsen, graduate research assistant at Washington State University. Wild oat seeds were broadcast at a rate of 60/yd² before seeding. Herbicides were not used to control grass weeds, allowing full weed competition with the crop. The trial was seeded with a research no-till drill that could band the fertilizer 2 inches below the seed.

Table 1 illustrates the effects of 75 pounds/acre of nitrogen fertilizer surface broadcast or banded below the seed at seeding time, Over twice as many wild oat plants were present on the broadcast treatments compared to deep banding. This apparent stimulation of wild oat germination by broadcast nitrogen has commonly been reported by other researchers. The difference in wild oat populations, wheat plant dry weight, wheat nitrogen uptake and grain yields were all significantly different between the two treatments. Although the trend was toward reduced wild oat plant dry weight and nitrogen uptake with the deep-banded fertilizer treatment, the reductions were not statistically significant.

Cochran and other researchers have been comparing the effect of nitrogen fertilizer placement on grass weeds (primarily downy brome) and winter wheat under conventional tillage, shallow rototilling and no-till from 1980 to 1984. The fertilizer was surface broadcast or banded either 2 inches directly below the seed, or 2% inches between a 5-inch paired-row (5:15 inch) and 2 inches below the seeding depth. Grass weeds were not removed with herbicides, allowing them to compete with the crop for available nutrients. Study sites were located near Pullman and Colton, WA.

A significant decrease in grass weed growth and nitrogen uptake was found in only 1 of the 4 years. Table 2 shows the results of the fertilizer placement-grass weed study under no-till winter wheat after spring wheat near Pullman in 1982. The dominant grass weed was downy brome. Nitrogen fertilizer was banded 2 inches below the seed or surface broadcast. Although differences were not always statistically significant, deep banding fertilizer consistently decreased weed dry weight and nitrogen uptake compared to broadcast. Banding also increased wheat dry weight, nitrogen uptake and grain yield at all of the fertilizer rates.

In these 4 years of research studies, deep banding nitrogen fertilizer increased winter wheat grain yield an average of 5 bushels/acre over broadcast without grass weed control measures over all three tillage treatments. Weed free plots yielded an average of 15 bushels/acre more wheat than comparable weed-infested plots. These results indicate that deep placement of fertilizer does increase wheat growth and yield, and give the crop a competitive advantage over the weeds. It is not a substitute for good weed control practices but can compliment them. Crop competition is important for achieving good grass weed control with most herbicides. The increased crop vigor and growth with deep banded fertilizer does improve the crop’s competitive ability for more effective weed control.

Table 1. Wild oat and no-till spring wheat response to broadcast and deep banded nitrogen fertilizer, Pullman, WA, 1980-81.

Fertilizer placement/weed control research will be continued by Cochran and other researchers. Alex Ogg, a new STEEP researcher and new leader of the USDA-ARS weed research group at Pullman plans several projects. One will evaluate the effect of fertilizer placement on grass weed populations; specifically, nitrogen uptake by downy brome in relation to the distance the weed is from the deep fertilizer band. Another study will evaluate the effect of plant row geometry (paired-row vs. constant row spacing) on the interference capability of annual grass weeds.

Table 2. Effect of nitrogen rate and placement on grass weeds and no-till winter wheat without grass weed control, Pullman, WA 1982.