Paired-row vs. Single Row Spacing

Chapter 6 – Fertility, No. 7, Winter 1987

Roger Veseth

The number of commercial no-till and minimum tillage drills has greatly increased in the 1980’s. Besides being designed to seed through a variety of crop residue levels and soil conditions, most of the drills are capable of deep banding fertilizer as well. Many growers have also built their own one-pass seed and fertilizer application equipment. Much attention has been focused on seed-fertilizer band orientation with paired-row spacing becoming a common option. Little research information, however, is available on paired-row. One important potential advantage is early root access to banded fertilizer.

Background Research

Several STEEP researchers have been involved in developing fertilizer placement technology in conservation tillage systems. One critical research area has been in developing a better understanding of leaf, tiller and root growth pattern of cereals. This research has been lead by plant physiologist Betty Klepper and soil scientist Ron Rickrnan, as well as other researchers at the USDA-ARS Columbia Plateau Conservation Research Center near Pendleton, OR.

Their research has shown the potential importance of the seminal root system early in the plant development (Fig. 1). Before the early 4-leaf stage, the seminal or primary roots, which develop from the seed, must supply all the plant’s water and nutrient requirements. As the tillering begins near this 4-leaf stage, crown roots begin to develop. Corresponding sets of crown roots develop for each tiller, eventually comprising the bulk of the cereal root system. With adequate soil moisture and time these crown roots can explore the soil between rows at or above seed depth, as well as extend to depths of 6 feet or more depending on soil conditions.

The lateral extent of the seminal root system, in contrast, is quite limited. Klepper and Rickman’s research indicates that seminal roots typically only extend laterally about 2 to 4 inches by the start of tillering. The roots also initially grow at a downward angle of about 30 to 45 degrees before they begin to grow straight down. Because of this downward growth angle and limited lateral growth, fertilizer banded more than a few inches from the seed row may not be available to the plant until the tillering stage when crown roots develop.

Their research on plant development patterns has shown that plant stress, before tiller emergence, can prevent tillers from forming. This stress may be from nutrient deficiencies, root diseases or environmental factors. They have found that stress as early as during the 2- to 3-leaf stage can result in loss of the first tiller, which is one of the highest producing tillers. Early fertilizer access could improve tiller survival in cases where soils have low nutrient levels.

Yield Response Example

Although many factors influence crop response to applied fertilizer, placement for early access to the seminal root system can be an important factor. An example of the impact that early access to fertilizer can have on wheat yield is shown in STEEP research by Gary Hyde, Washington State University agricultural engineer. The research was conducted near St. John, in a 16-inch precipitation zone and near Pullman, in a 20-inch precipitation zone (Table 1).

Yield increases of 13 bu/acre winter wheat and 11 bu/acre in spring wheat were achieved by banding the fertilizer below the seed compared to fertilizer banded between the 16-inch seed rows. Fertilizer below the seed is immediately available to the first seminal root (radicle), even before plant emergence. In contrast, fertilizer banded between the 16-inch seed rows was probably not available until the tillering stage when crown roots have developed. Hyde believes this was the major factor in lowering yields as fertilizer banded 8 inches from the seed row was not adequately available to the plant roots under the growing conditions tested.

Paired-Row Comparison

Besides fertilizer banded below the seed, band placement near the seed row below seed depth can also provide early seminal root access to fertilizer. One effective way to use this method of fertilizer banding has been through paired-row systems where one fertilizer band is placed between two closely spaced rows so that it is within 2 to 3 inches of each seed row (Fig. 2). The fertilizer band should also be at least 2 inches below seed depth because of the 30 to 45 degree downward growth angle of the pairs of seminal roots, and to ensure placement into moist soil.

Hyde recently conducted field research comparisons of no-till wheat response to fertilizer banded below the seed in a 16-inch row spacing and fertilizer banded below seed depth between 4-inch rows in a 4: 12-inch row spacing. He used a modified, John Deere HZ deep-furrow drill with 16-inch spacings. Parabolic knives between the packer wheels placed fertilizer 2 inches below seeding depth.

With below-the-seed fertilizer placement, seed was placed either with the same parabolic knife or with a trailing double disk opener and packer wheel. For paired-row spacing, double disk openers and packer wheels were placed behind and to the side of the deep furrow packer wheels, 2 inches to each side of the fertilizer knife.

Table 1. Effect of fertilizer band placement on wheat yield in a no-till winter wheat-spring wheat rotation at Pullman and St. John, WA, with 16-inch spacing deep-furrow drill, 1983 (Hyde, WSU).

In 1986, Hyde found no statistical differences in no-till wheat yield between fertilizer below the seed in 16-inch seed row spacings, and below seed depth — between 4-inch rows in the 4: 12-inch paired-row spacing at two locations (Table 2). This supported research results from 1985 where no statistical yield differences were found between the same fertilizer placement-row spacing combinations in no-till spring wheat studies at St. John and Pullman. Hyde concludes that fertilizer placement below the seed, or below seed depth a few inches to the side of the seed (as between paired rows) can both be equally available to the seminal roots. He cautions that a 2-inch minimum soil separation be maintained between the seed and fertilizer, especially when anhydrous ammonia is applied.

Table 2. Wheat yield response to fertilizer banded 2 inches below the seed In 16-inch seed row spacing compared to 2 inches below seed depth –between 4-inch spaced seed rows In a 4:12-inch paired-row spacing, no-till spring wheat-winter wheat rotation, 1986, St. John and Pullman, WA (Hyde, WSU).