Maximizing wheat yields in North Dakota in a crop rotation system
An evaluation of the effect of crop rotations on wheat yield and quality.
IPNI-1982-USA-ND2
21 Jun 2001
Justification
- North Dakota is a leading state in the production of wheat. This status has come about as the result of large acreage and improvement in management techniques. State averages, however, are somewhat lower than what the technology available to obtain maximum yields would indicate. This suggests that the combination of factors needed for maximum yields have not been correctly identified or uniformly applied. The overriding production factor in North Dakota is climate and is often given as the explanation for the wide variation and inconsistency of yields. Yet under ideal climatic conditions the anticipated maximum yields are not always achieved.
Maximum yield levels are determined by the most limiting factor. The most limiting factor in North Dakota is and will continue to be moisture. Other factors like weed control, disease and insect control, inherent soil fertility, fertilizer applications, tillage system and agronomic factors (variety selection, seeding rate and date, seed size and uniformity, and row spacing) will ultimately affect yield depending on the management level. A reduction from maximum imput in any one of these management areas could affect yield. The average wheat producer may only put his emphasis on one or two of these management factors in achieving his yield goal. The factors emphasized may or may not be limiting his yield level. However, the producer must believe each specific management factor or combination of factors will contribute significantly to yield increases before they are implemented. There is a need to identify those factor combinations that will achieve maximum yields over varied climatic, soil and crop rotation systems. Identification of the best factor combination becomes very difficult because of the large number of variables involved. An experiment that contains combinations of all management variables would be astronomical, thus the best approach is to eliminate those variables from the study that previous research have shown to limit yield and then maximize imput for these variables. Emphasis can then be place on a limited number of interrelated variables upon which additional research information is required to access their contribution to maximum yield.
By making some basic assumptions based on research work, a large number of variables can be held constant at their maximum benefit. For example, soil moisture is critical in achieving maximum yields; this, a study needs to incorporate those management practices that maximize soil water retention (snow trap) and minimize its loss (reduced tillage). Lack of weed control reduces yield because of plant competition for moisture and soil nutrients, thus maximum weed control is essential. If maximum weed control is maintained, then weed control as a variable can be eliminated from the experiment.
Agronomic characteristics like variety, seeding rate and date, seed size and row spacing have all been shown to influence wheat yields. By selecting the ideal row spacing, large viable seeds and the maximum population (based on previous research trials), these variables can be applied uniformly to the trial and thus eliminated as a significant variable assuming no interaction with other management variables. Planting date is extremely important and interacts with variety and climate. Research has shown that early plantings out perform late plantings; thus, planting time should be consistent with the earliest date that soil and climatic conditions dictate. the interaction of planting date with climate can partially be evaluated by using varieties with wide differences in maturity. Also, the question of variety interaction with other management variables still remains unresolved. Limited studies have been conducted in north Dakota with N fertilizer x variety interactions, variety trials on fallow versus recrop. All these trials were year specific or conducted at different locations or sites each year for a number of years with no measure of the previous management or fertilizer residual effects in a crop rotation system on the same site as practiced under normal farmer operations.
Plant diseases have been shown to cause significant yield losses in wheat but the incidence of disease is often related to climatic conditions and control measures (variety resistance, crop rotation or spraying of foliar fungicies) practiced. Questions still remain unanswered about the interaction of disease with current management systems, the effect of foliar fungicides on maximizing yield and the influence of chlorides on the reduction of root rot diseases when applied as potassium chloride.
Numerous fertilizer trials have been conducted on wheat in North Dakota and the N and P requirements of the crop are well established and recommendation established based on soil test levels. Potassium is usually not recommended for wheat because the soils test high and research has shown little response to application of potassium fertilizer. Recent work suggests that wheat may respond to the fertilizer even on high testing soils. Thus, potassium fertilizer needs to be considered as a variable since the question remains unresolved, especially when trying to achieve maximum yields with other management imputs at their maximum.