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WHEAT PRODUCTION SYSTEMS FOR SOUTHWESTERN NORTH DAKOTA

P. Carr, Associate Agronomist, Dickinson Research Extension Center
G. Martin, Research Technician, Dickinson Research Extension Center
B. Melchior, Ag Research Technician, Dickinson Research Extension Center
L. Tisor, Research Technician, Dickinson Research Extension Center
M. McMullen, Professor, Plant Pathology, NDSU, Fargo, ND
J. Kuprinsky, USDA Agriculture Research Service

SUMMARY

The wheat-black fallow rotation has been used extensively as a production strategy for spring wheat in western North Dakota and throughout the Great Plains. There are several benefits the black fallow period provides: organic nitrogen can be mineralized, weeds can be mechanically controlled, soil water recharge can occur, and crop loss risk can be reduced and farm income stabilized (Smika, 1970). Along with these benefits have come costs, including the formation of saline seeps, uncontrolled wind and water erosion, and reduced soil nutrient levels over time (Haas et al., 1957; Halvorson and Black, 1974). Moreover, the idling of productive land in a wheat-black fallow rotation has raised economic efficiency questions (Ali and Johnson, 1981). Soil conservation mandates, as exemplified by the Conservation Compliance Provision of the 1985 Farm Bill, suggest that alternatives to the wheat-black fallow rotation must be developed for the long-term viability of wheat production in North Dakota.

OBJECTIVES

1. Determine how cultivar selection and seeding rate affect spring wheat performance across wheat-black fallow, wheat-ecofallow, and wheat-chemical fallow systems.
2. Evaluate N fertilizer and N fertilizer by fungicide interactions for tan spot suppression, grain yield and phenotypic response in continuously cropped environments.
3. Compare the agronomic performance of several spring wheat cultivars across wheat-black fallow, wheat-wheat, and wheat-corn rotations

INTRODUCTION

Objective 1

Most hard red spring wheat is sown on black-, eco-, and chemical-fallow in the Southwest Crop Reporting District (Beard and Hamlin, 1996). Generally several cultivars are sown each year, depending on seed costs, seed availability, and other factors (Solemaas, ASCS, per. comm.). A cultivar (C) by tillage system (TS) interaction has not been considered across fallow environments even though a C by TS interaction has been reported across recropped environments (Ciha, 1982). Knowledge of a C by TS interaction across different fallow environments would aid producers in selecting cultivars best suited to their fallow management strategies. Also needed is information on whether seeding rates (SR) should be adjusted according to the cultivar and tillage system used. Knowledge about C by TS and C by TS by SR interactions might result in more efficient spring wheat production in reduced- and no-till systems.

Objective 2

An alternative to a spring wheat-black fallow rotation is to grow wheat continuously. A benefit of continuous wheat compared to alternating wheat and fallow is that productive land is not idled. However, Tan Spot (incited by Pyrenophora tritici-repentis [Died.] Drechs.) can be a major pest in continuous wheat systems because this fungus overwinters in crop stubble. Tan spot and other fungal infestations can be accentuated in reduced-till and no-till systems. These fungi must be controlled for profitable wheat production.

Nitrogen (N) fertilizer applications have sometimes reduced outbreaks of tan spot in winter wheat (Huber et al., 1987), but the ability of N applications to suppress tan spot in spring wheat has not been demonstrated. Similarly, N fertilizer by tillage system interactions have not been identified regarding tan spot. Knowledge about these interactions would support profitable production in fields where wheat is grown during two or more continuous years.

Objective 3

Spring wheat cultivars respond differently in contrasting environments. It is unclear how wheat grain yield and quality, and other phenotypic characteristics, are influenced by cropping sequence. North Dakota producers need this information as they explore alternatives to black fallow in a wheat-black fallow rotation. Understanding the cultivar by crop rotation interaction is needed to explain why crop yields vary in regions of the state where rotations differ.

MATERIALS AND METHODS

Objective 1

A field experiment was conducted under dryland conditions at Dickinson in 1995 and 1996. Plots were arranged in a modified randomized complete block design in a split split-plot arrangement. Tillage system comprised main plots, seeding rate comprised subplots, and spring wheat cultivar comprised sub-subplots. Tillage systems included: (1) conventional-till (spring disking and leveling with a cultivator and culti-harrow until less than 5% of residue remains at the soil surface at planting); (2) reduced-till (leveling with a cultivator and culti-harrow in attempts to maintain between 30%-60% of residue at planting); and (3) no-till (direct sowing into standing stubble). Subplots consisted of seeding rates of 500,000, 1,000,000, and 1,500,000 PLS per acre. Sub-subplots consisted of 2 conventional height (AC Minto, Amidon) and 3 semidwarf (Bergen, Grandin, Norm) spring wheat cultivars representing a range of genotypes and phenotypes presently grown in the northern Great Plains Region.

Both phases of each tillage system (crop and fallow) were established and will be maintained throughout the trial's duration. As a result, 50% of the space allocated for plots is not planted in any year (i.e., fallow plots); weeds in these plots are either mechanically controlled (conventional-till), controlled both mechanically and with herbicides (reduced-till), or controlled solely using herbicides (no-till).

Main plots were 4500 square feet (90 by 50 ft). There were 6 main plots per replicate and four replicates in the experiment. Sub-subplot dimensions were 50 by 6 ft.

Plant nutrients were supplied as needed for a grain yield goal of 60 bu per acre, based on soil test results.

Post-emergent herbicides were used during the crop phase in conventional- and reduced-till systems to control weeds. In the fallow plots, mechanical cultivation was used to control weeds in the conventional-till system. Two herbicide applications and a light disking were used in the reduced-till system. Non-incorporated herbicides were used in the no-till system.

Variables measured on each cropped plot included: number of plants at emergence, plant height, grain yield, 100 kernel weight, grain volume weight, and grain protein content. Number of tillers at the six-leaf stage were counted, as were the number of heads that had developed on wheat plants at physiological maturity.

Data were analyzed using a computer-driven statistical program.

Objective 2

The experiment was arranged in a randomized complete block design in a split split-plot arrange-ment. Tillage system comprised main plots, fungicide treatment comprised subplots, and N applications comprised sub-subplots. Tillage sys-tems were established as described for Objective 1.

A single application of mancozeb at 1.0 lb a.i per acre along with a control (no fungicide) constituted subplot treatments. Applications of mancozeb at this rate may be economical in western North Dakota if severe tan spot infestations exist. The fungicide treatment was also used to assess if applications of N fertilizer were effective in suppressing tan spot.

Nitrogen as ammonium nitrate was applied, based on soil test results, at high and low rates. The high rate corresponded to a fertilizer plus soil N amount of 100 lbs N per acre and the low rate to 50 lbs N per acre.

Main plots were 2200 square ft. Sub-subplot dimensions were 55 by 10 ft. There were four replicates.

The following variables were measured on each plot: foliar leaf spotting at anthesis, plant height, grain yield, 1000 seed weight, and grain volume weight. Data were analyzed using a computer-driven statistical program.

Objective 3

The experiment was arranged in a modified randomized complete block design in a split-plot arrangement. Cropping sequence comprised main plots and consisted of wheat-black fallow, wheat-wheat, and wheat-corn rotations. Five conventional-height cultivars (AC Minto, Amidon, Butte 86, Sharp, Stoa) and five semidwarf spring wheat cultivars (2371, Bergen, Grandin, Hi Line, Norm) comprised subplots treatments.

Both phases of wheat-black fallow and wheat-corn rotations were established in 1994 and will be maintained throughout the trial's duration. Hence, two main plots will be maintained each year for both rotations. By having both phases represented each year, wheat grain yield and quality data will be generated annually by each rotation. These data can then be compared with that produced by the wheat-wheat rotation each year the experiment is conducted.

Main plots were 1680 square feet. There were five main plots per replicate (two each for both wheat-black fallow and wheat-corn rotations and one for the wheat-wheat rotation). There were four replicates. Subplot dimensions were 6 by 28 ft.

Variables measured on each plot included: plant height, grain yield, 100 kernel weight, grain volume weight, and grain protein content.

The data were analyzed using a computer-driven statistical program.

RESULTS

Objective 1

Seeding wheat at 500,000 PLS per acre resulted in a lower grain yield than seeding wheat at either 1,000,000 or 1,500,000 PLS per acre in each year across the three tillage systems. Seeding wheat at 1,500,000 PLS per acre produced more grain with heavier test weight than seeding wheat at 1,000,000 PLS per acre in 1995, but not in 1996.

Grain yield did not vary across the three tillage systems in either 1995 or 1996. The hard spring wheat cultivars varied for each factor considered in both years, except for the number of tillers formed at the six-leaf stage in 1996. A cultivar (C) by tillage system (TS) interaction generally did not occur for any factor considered.

A C by seeding rate (SR) interaction occurred for grain yield in both years the experiment was conducted. A C by SR interaction also existed for returns ($/acre) in each of the two years. A C by SR by TS interaction generally did not exist for any factor in both years in which the experiment was conducted.

Objective 2

Applications of mancozeb failed to reduce leaf spotting in two of the three years in this trial when leaf spotting was determined. Similarly, tillage environment failed to affect grain yield in most years. Application of N fertilizer increased grain yield in 1994 and 1995, but not in 1993 or 1996. Nitrogen fertilizer did not affect leaf spotting in the years when fertilizer was applied and leaf spotting was determined.

Suppression of leaf spotting from applications of N fertilizer on hard red spring wheat was not demonstrated in this experiment.

Objective 3

Grain yield has not varied whether wheat follows corn, fallow, or wheat in 1994, 1995, or 1996. However, a wheat cultivar (C) by cropping sequence (CS) interaction existed in both 1994 and 1996 for grain yield and returns. Returns were higher when the semidwarf cultivars were grown following corn than when the conventional-height cultivars were sown following corn in 1994. In this same year, returns were higher when the conventional-height cultivars were sown after fallow than when the semidwarf cultivars were planted. Comparable returns were generated by both cultivar groups in a wheat-wheat system.

Returns were higher when the semidwarf cultivars were seeded after fallow than when conventional-height cultivars were seeded after fallow in 1996. Returns were similar among both cultivar groups when seeded after corn or wheat in 1996.

LITERATURE CITED

Ali, M.B., and R.G. Johnson. 1981. Economics of summerfallow - wheat systems in North Dakota. North Dak. Agric. Exp. Stat. Bul. 511.

Beard, L.W., and W.G. Hamlin. 1996. North Dakota agricultural statistics. Bull. No. 65. North Dak. State Univ. Agric. Expt. Stat. and U.S. Dept. Agric. Ag. Stat. Fed. Bldg., Fargo, ND.

Black, A.L., and J.F. Power. 1965. Effect of chemical and mechanical fallow methods on moisture storage, wheat yields, and soil erodibility. Soil Sci. Soc. Amer. Proc. 29:465-468.

Ciha, A.J. 1982. Yield and yield components of four spring wheat cultivars grown under three tillage systems. Agron. J. 74:314-320.

Halvorson, A.D., and A.L. Black. 1974. Saline-seep development in dryland soils of northeastern Montana. J. Soil Water Cons. 29:77-81.

Huber, D.M., T.S. Lee, M.A. Ross, and T.S. Abney. 1987. Amelioration of tan spot-infected wheat with nitrogen. Plant Dis. 71:49-50.

Smika, D.E. 1970. Summer fallow for dryland wheat in the semiarid Great Plains. Agron. J. 62:15-17.

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