Fertilizer Placement Can Reduce Root Disease Effects

Chapter 4 — Disease Control, No. 15, July 1991

Roger Veseth

Northwest research projects on conservation tillage have commonly shown that deep banding of required fertilizer near the seed row for early cereal root access can increase yields. Soilborne root diseases can influence cereal response to fertilizer placement, but this interaction usually has not been considered in the research. Studies now have shown that fertilizer placement is a potential management tool for Northwest wheat and barley growers to minimize yield losses due to soilborne root diseases under conservation tillage.

Recent research by R. James Cook of the Agricultural Research Service at Pullman, WA shows that, where root diseases are a problem, deep banding of required nitrogen, phosphorus and sulfir fertilizer below each seed row can significantly increase yields compared to banding between alternate seed rows. Increased growth and yield response to fertilizer placement occurred under high root disease potential with cereals planted after cereals using a one-pass planting system. With soil fumigation to eliminate root pathogens, the location of the fertilizer band did not affect yields – showing the importance of root diseases in cereal responses to fertilizer placement options, The research has been conducted at several Inland Northwest locations over the past 3 years.

Development of management strategies to minimize the effects of cereal root diseases under conservation tillage systems has been a major focus of Cook’s research over the past 2 decades. Cook is a plant pathologist and research leader at the ARS Root Disease and Biological Control Research Unit at Washington State University in Pullman. His research has been supported by the Washington Wheat and Barley Commissions and the O. A. Vogel Wheat Research Fund. It has been conducted in cooperation with the STEEP (Solutions To Environmental and Economic Problems) conservation farming research effort in the Pacific Northwest.

Root Disease Impacts

Cook’s one-pass planting system with fertilizer shanked below each seed row reduced yield losses from the effects of the three major root diseases of cereals in the Northwest. These diseases are take-all of wheat, and Rhizoctonia root rot and Pythium root rot of both wheat and barley. Cook points out that any one or combination of these root diseases can be significant constraints to cereal productivity in Inland Northwest cropping regions receiving about 15 inches or more annual precipitation and under irrigation.

Although these diseases can reduce cereal yields in any tillage system, the potential for disease losses is greatest where cereals are planted after cereals with surface residue, which is typical of conservation tillage. Cook explains that cereal residue left on the soil surface acts like a’ ‘wet blanket” to keep the topsoil moist, a condition ideal for these root pathogens. Root disease potential is greatest when host plants, in this case cereals and most grass weeds, grow more frequently in the crop rotation. Another factor causing greater disease severity, particularly Pythium and Rhizoctonia root rots, under these cropping conditions is the presence of volunteer cereals and grass weeds becoming as a “green bridge” between harvest of one crop and planting of the next crop. Pythiwn and Rhizoctonia use the roots of volunteer cereals and weeds as their primary source of nutrients and use crop residue less effective.

When is Fertilizer Placement Important?

A primary consideration for cereal fertilizer applications should be soil nutrient availability. Fertilizer placement decisions should then be based on soil temperature, soil nutrient mobility, expected precipitation and other factors affecting root uptake, Root disease severity and root health also effect root uptake of nutrient, as shown in Cook’s research. Cook points out that shanking fertilizer below each row with one-pass methods of planting works across all crop rotations, but may have the greatest cereal yield benefit with no crop rotation and high root disease potential.

Many management practices can help minimize the effects of soilborne root diseases and optimize plant health and yield potential under conservation tillage systems. Following are several examples of management options and how they may affect cereal response to fertilizer placement in one-pass planting systems.

Effects of Crop Rotation

Field research around the Inland Northwest by Cook has confirmed that 3-year crop rotations, particularly those with non-cereal crops or a period of fallow free of growing plants, are one of the most effective management practices for controlling cereal root diseases under conservation tillage.

Cook has used soil fumigation to eliminate root pathogens and to show the effect of root diseases on yield in relation to crop rotation. He stresses that soil fumigation is a research tool and is not practical or economical for commercial cereal production. The results have clearly shown the beneficial response of crop rotation for management of these diseases in dryland cropping areas with 15 or more inches of annual precipitation or under irrigation. He has documented a 70 percent average yield response of winter wheat to soil fumigation since 1974 in field experiments where wheat had been grown for at least the previous three consecutive years without crop rotation. In contrast, the yield response in other sites to soil fumigation has averaged 20 to 25 percent where wheat had been grown every other year (in 2-year rotations) with dry peas or lentils in the alternate years, and only 5 to 10 percent in fields where wheat had been grown every third year (in 3-year rotations) following spring barley and then dry peas or lentils.

Unfortunately, the use crop rotation to reduce cereal root diseases under conservation tillage can be limited. Changes in the USDA farm programs, inadequate precipitation, yearly climatic variations, limited alternative rotation crops and markets, and other factors all influence crop rotation options. When longer crop rotations are not feasible, other root disease management options become more critical. Cook’s recent research on the importance of deep banding of fertilizer below the seed row provides growers with an additional tool for managing root diseases under conservation tillage. He points out that fertilizer placement becomes less important where longer crop rotations improve root health.

Effect of the “Green Bridge”

When growers recrop spring cereals after cereals under conservation tillage, elimination of the volunteer cereals and other weeds well ahead of seeding is another management option which can influence the importance of fertilizer placement for reducing damage from root diseases in one-pass planting systems for cereals. Cook explains that volunteer cereals and weeds become a “green bridge” for soilborne root pathogens and possibly other pests between the harvest of one crop and planting of the next. As the volunteer and weeds die from a herbicide application, populations of root pathogens increase dramatically as they “take over” the dying plant roots. With time, populations of’ “beneficial” residue-decomposing microbes increase and populations of root pathogens decrease. If the next cereal crop is planted directly into the dying volunteer cereals and weeds, when root pathogen populations are increasing, damage from root diseases can be severe. Cook stresses that this “green bridge” can be a cause of the all-too-familiar combine row effect, once thought to result from toxic chaff, but now thought to result from the increased populations of root pathogens on volunteer cereals and grass weeds concentrated in the combine chaff row.

Research by Cook and other Northwest researchersshows that a non-selective herbicide application for volunteer cereals and weeds at least 2 to 3 weeks ahead of seeding spring cereals can significantly reduce the incidence of Rhizoctonia root rot in particular, but possibly also take-all and Pythium root rot under conser

vation tillage systems. Spraying out volunteer cereals and grass weeds the previous fall has resulted in even less root disease and higher yields in some experiments. Cook’s research shows that fertilizer placement below each seed row in a one-pass planting system is most critical where volunteer cereals and grass weeds are sprayed out only 2to 3 days before seeding — the situation most favorable to root disease.

Cook’s research has not shown any advantage of early vs. late elimination of the volunteer and weeds when winter wheat in direct-seeded after winter or spring wheat. Apparently, the reservoir of disease inoculum on the roots of the wheat just harvested is not significantly enhanced by the brief period of volunteer growth before recropping with winter wheat.

Effect of Seeding Date and Seed Age

Where Pythiwn is a problem in winter wheat production, Cook points out that growers can reduce disease losses through selection of seeding date and seed age. Planting winter wheat slightly earlier (possibly 7 to 10 days) in warmer, well-drained soils can significantly reduce Pythium infection of germinating seed. Pythium thrives under cool, wet conditions typical of late fall winter wheat seeding, and is less active in drier, warmer soils.

If the seeding is delayed, Cook’s research demonstrates the advantages of using high-quality new seed because of its greater avoidance of Pythium infection under cool, moist conditions. Cook explains that, when older, lower-quality seeds absorb water in the soil, they tend to “leak nutrients” that stimulate Pythium growth and infection. Seed age is less important under warmer, drier conditions. On the other hand, new seed with high temperature-dormancy should not be used when seeding early on summer fallow in very warm soils.

Reviewing Management Options

In light of these other management options for reducing soilborne root diseases of cereals under conservation tillage, growers should be better able to determine the relative importance of fertilizer placement on overcoming the effects of root diseases in their farming operations. Different management options may increase or reduce the need for fertilizer banding for early root access in order to minimize the yield-depressing effects of cereal root diseases. Aside from potentially reducing yield losses from root diseases, banding fertilizer for early cereal root access can often increase emergence and establishment rates, improve fertilizer use efficiency and reduce fertilizer losses.

Research Focus on Fertilizer Placement

Cook’s research on fertilizer placement in one-pass planting systems focuses on the idea that root diseases can limit early root growth and consequently limit water and nutrient uptake. Early access to fertilizer may stimulate root growth and enable the plant to”outgrow” some effects of the root diseases. Phosphorus is known to be particularly important for rapid, vigorous root growth.

The importance of the in-row soil disturbance that occurs from fertilizer shanks ahead of each opener is still not known. Cook points out that research in Australia indicates that even a single tine disturbing the soil within the seed row and below the depth of the seed can significantly reduce the impact of Rhizoctonia root rot when cereals are direct-seeding into wheat stubble or pasture. He plans further research beginning in 1991 on the relative importance of root access to fertilizer compared to in-row soil disturbance from the fertilizer shank.

Again, Cook used soil fumigation as a research tool to help separate the effect of fertilizer placement below the seed row on root disease from the effect on the crop itself. In other words, without root disease, does fertilizer placement below the seed row have any effect on crop growth and yield potential compared to placement several inches away from the seed row?

Cook has conducted field research with the one-pass planting method at several Inland Northwest locations over the past 3 crop years with spring wheat, winter wheat or spring barley. Field research sites have been located near Pullman, Faitileld and Lind, WA, and Pendleton, OR.

One-pass Planting Equipment

The one-pass drill used by Cook in his research has l-inch wide fertilizer shanks staggered on two toolbars ahead of double-disk Acra-Plant seed openers on a third, following toolbar. The shanks deep-band liquid fertilizer 2 to 3 inches below seeding depth. Both the fertilizer shanks and seed openers are adjustable laterally on the toolbars to allow comparison of different row spacings and fertilizer shank-seed row spacing arrangements. In 1990, two seed row spacings were compared with two fertilizer shank spacings: (1) uniform 12-inch row spacing with fertilizer shanks on either 12-inch spacings (directly ahead of the seed openers) or 24-inch spacings (between rows); and (2) a 7:17-inch paired-row spacing with fertilizer shanks either paired on the same spacing (directly ahead of each pair of seed openers) or on 24-inch spacing (between the 7-inch pairs of seed openers). Cook points out that the drill row spacing growers use will vary with precipitation zone, water availability, weed competition, surface residue amount and other factors. Wide row spacings can make it more difficult to control weeds.

Paired-row Fertilizer Arrangement

Inprevious years of the experiments, Cook compared the 12-inch and 7: 17-inch paired-row spacings with a fertilizer shank directly ahead of each row in the 12-inch spacing and between each 7-inch pair of rows in the 7:17-inch paired-row spacing. This latter combination is the typical fertilizer band arrangement in most commercial conservation tillage drills with paired-row seeding, although specific row spacing is variable. Under natural soil conditions, yields with these two treatments were either not different or were higher with the uniform 12-inch row spacing than the paired-row spacing. To determine if the effect was from row spacing or position of the fertilizer shank, Cook evaluated fertilizer placement below each seed row in both row spacings in 1990.

1990 Research Results

Spring Wheat at Pullman, WA

The research site near Pullman is in a 20-inch annual precipitation zone on Palouse silt loam soil. To test management options under severe pressure from soilborne root diseases, Cook has grown continuous notill wheat with the volunteer wheat plants sprayed with a non-selective herbicide only 1 to 3 days before seeding. The 1990 spring wheat crop planted after winter wheat was the 7th no-till wheat crop in 8 years. The previous 3 years were continuous winter wheat followed by spring wheat in 1990.

Spring wheat yields were significantly higher in both the uniform 12-inch and 7:17-inch paired-row spacings where the fertilizer shanks were placed directly ahead of the seed openers (within the seed rows) compared to between openers (Table 1). However, where the soil was fumigated, yields in response to fertilizer placement treatments were not significantly different. Row spacing alone did not significantly influence yield on either the natural or fumigated soil.

Table 1. Influence of row epecing and fertilizer placement on the yield of epring wheat direct-eeeded after winter wheat during the 4th year of contlnuoue no-till whaat in natural and fumigated soil near Pullman, WA, 1990. The volunteer wheat and weede were aprayed with a non-aelactlve herbicide 2 daya before seeding to increaae root disease potential. (Cook, ARS).

Fig. 1. Effect of fertilizer placement on the severity of Rhizoctonia root rot (”bear patch”) in a continuous no-till spring barley study in 1990 near Lind, WA. The disease was more severe where the fertilizer was deep banded between 12-inch seed rows (right) than where the fertilizer was deep banded directly below each seed row (left) .(R. J. Cook, USDA-ARS, Pullman, WA).

Table 2. Influence of row spacing and fertilizer placement on the yieid of spring barley direct-seeded during the 5th year of continuous no-till spring barley in natural and fumigated soil under supplemental irrigation near Lind, WA, 1990. Volunteer barley was sprayed with a nonselective herbicide 4 days before seeding to increase Rhizoctonia root rot potential. (Cook, ARS).

Irrigated Spring Barley at Lind, WA

Cook’s experimental site near Lind is at the WSU Dryland Agricultural Research Unit on Ritzville silt loam in a 9- to 10-inch precipitation zone. However, this site, with continuous no-till spring barley, is under supplemental irrigation to simulate conditions in the 15- to 20-inch precipitation area. The 1990 crop was the 5th consecutive year of no-till spring barley. To intensify root diseases, primarily Rhizoctonia root rot in this case, Cook broadcast spring barley seed on the soil surface in the fall to provide” wall-to-wall” volunteer. The volunteer barley “green bridge” was sprayed out 4 days before seeding.

Fertilizer shank and seed opener spacing was the same as the Pullman spring wheat trial. Results (Table 2) were also similar to those of the Pullman trial. In the 7:17-inch paired-row spacing, placement of the fertilizer shanks ahead of each seed opener resulted in significantly higher yields than placement between the 7-inch pair of rows. Although there was a trend toward higher yields with fertilizer shanks ahead of each seed opener than between alternate rows in the 12-inch row spacing, the yield difference was not statistically significant.

In fumigated plots, there were no significant yield differences between fertilizer placement treatments. Consequently, Cook believes the fertilizer placement helps the crop grow and produce despite root diseases, and placement has less direct effect on the crop itself in the absence of root disease. Again, row spacing alone did not significantly influence yields in either natural or fumigated soil.

Summary and Future Plans

Cook’s research has demonstrated that deep banding of fertilizer nutrients below each seed row using one-pass planting systems can increase cereal yield potential where root diseases are a problem. He points out that crop response to fertilizer placement can vary with other management practices used to reduce root diseases, such as longer crop rotations, early elimination of the green bridge, seeding date and seed age/quality, and other soil and the cereal response to environmental factors affecting nutrient mobility and availability. Cook plans to continue research on planting systems and other management options for reducing the effects of cereal root disease under conservation tillage. Future research will investigate the effect of in-row soil disturbance caused by fertilizer shanks below seed rows compared to the deep banded fertilizer.

Fig. 2. Effect of fertilizer placement on the severity of Rhizoctonia root rot (”bear patch”) in a continuous no-till spring barley study in 1990 near Lind, WA. The disease was more severe where the fertilizer was deep banded within the 7-inch pairs of rows in a 7:17-inch row spacing (left) compared deep banding directly below each seed row (right). (R. J. Cook, USDA-ARS, Pullman, WA).