Economic Optimal Rate Research Articles

An economic evaluation of site-specific herbicide application

The objective of this study was to determine if site-specific application of postemergence herbicide was economically viable with current technologies. This objective was accomplished by: developing an algorithm that determined the economic optimal postemergence herbicide rate; creating models to determine the impact that postemergence herbicide rate has on yield; and determining whether site-specific application of postemergence herbicide has greater net returns than those from a uniform application of postemergence herbicide. Weed species identification and population counts were done on a regular grid in five fields across Kansas. A decision algorithm was developed to determine the economic optimal rate of postemergence herbicide for each grid cell. The site-specific herbicide rate and four standard herbicide rates [0, 0.5, 0.75, and full (1×) label rate] were applied according to a split-plot design. Weed population observations made three weeks after application showed that the site-specific treatment controlled the weeds present in the fields. Production functions developed to determine whether postemergence herbicide rate had an impact on yield showed that it had a positive, yet statistically insignificant, effect on yield. The difference in estimated net returns between applications of site-specific rate and uniform full-label rate covered all of the costs associated with site-specific application of postemergence herbicide. The margin between the estimated net returns for site-specific and uniform application of the economic optimal rate covered only a portion of the costs associated with site-specific application of postemergence herbicide.

Economic and Environmental Impacts of Long-Term Nitrogen and Phosphorus Fertilization

Nitrogen and P fertilizers are needed for optimum production and economic returns from irrigated continuous corn (Zea mays L.) However, excessive application of N must be avoided to minimize adverse environmental impacts. The objectives of this study were to determine: (i) the economic optimum rate of N for irrigated continuous corn, (ii) how sensitive optimal N rates were to corn and N prices as well as yield potential, and (iii) the relationship of optimal N rate to profile nitrate-N accumulation. Yield data from a long-term study were used to estimate quadratic production functions, with and without P, for corn yield as a function of N rate. Six rates of N (0, 40,80,120,160, and 200 lb/acre) and two rates of P2O5 (0 and 40 lb/acre) were applied annually from 1961 to 1991 on a Ulysses silt loam (fine silty, mixed, mesic, Aridic Haplustoll) near Tribune, KS. Without fertilizer P, soil P levels declined to deficient levels of about 7 ppm Bray 1-P. The economic optimal N rate, with P, was 159 lb/acre. Phosphorus fertilization increased the economic optimal N rate by about 15 lb/acre, while increasing maximum yields by almost 60 bu/acre, increasing maximum net revenue more than $130/acre, and decreasing minimum cost of production by $0.56/bu. The economic optimal N rate was similar for low-, medium-, and high-yielding years and application of insurance N reduced profitability. The economic optimal N rate was relatively insensitive to changing N and corn prices. Profile nitrate-N content was relatively low and essentially the same when N was applied with P at the economic optimal N rate or less. This indicates that applying N to maximize profit does not cause nitrate accumulation or leaching concerns. However, accumulation and movement of nitrate below the crop root zone increased when N was applied in excess of the economic optimal rate or without adequate P fertilizer. Research Question Efficient use of fertilizer N is important for maximizing profit and minimizing environmental risk from fertilizer derived nitrate-N. Although many soil, crop, and environment factors influence the quantity of soil profile nitrate-N that could be transported below the root zone, accurately estimating fertilizer N requirements is the most important factor. The objectives of the study were to evaluate the relationship between economic optimum N rate and residual fertilizer N accumulation in the soil profile and to determine the sensitivity of optimal N rate to changing N and corn prices as well as yield potential. Literature Summary In the Great Plains, N recommendation models generally are based on yield goal and preplant nitrate-N content in the soil profile. When yield goals are overestimated or profile nitrate-N is underestimated, the. predicted N rate is greater than that required for optimum grain yield, which reduces economic returns and can dramatically increase residual fertilizer N in the soil profile. Several studies have reported minimal carryover of residual fertilizer N when the application rate was nearly equivalent to the requirement for optimal yield. Study Description Nitrogen and P fertilizers were applied annually from 1961 to 1991 to irrigated continuous corn in western Kansas. Six rates of N fertilizer (0, 40, 80, 120,160, and 200 lb/acre) and two rates of P2O5 (0 and 40 lb/acre) were arranged in a randomized complete block design with five replications. Grain yield response to N and P was measured each year, and soil profile nitrate-N content (0 to 10 ft depth) was determined after harvest in 1990. A quadratic production function was estimated to describe grain yield response to applied N and P and to determine N rates at which yields and net returns were maximized and production costs per bushel were minimized. Applied Questions What is the economic optimum N rate for irrigated continuous corn in the central High Plains? In this long-term study, the economic optimum N rate was 159 lb/acre. Although fertilizer P increased net revenue by $130/acre, it had little effect on optimal N rate. Does the economic optimum N rate vary from year to year because of differences in yield potential? No, the economic optimal N rate was essentially the same for low-, medium-, and high-yielding years. Does the economic optimal N rate vary as fertilizer N and corn prices change? No, the economic optimal N rate was relatively insensitive to changing fertilizer N and corn prices. Does N fertilization at the most profitable rate cause nitrate-N accumulation and potential leaching problems? No. After 30 yr of N application with P, nitrate-N levels were very low when N was applied at the economic optimal rate with P (Fig. 1). Figure 1Open in figure viewerPowerPoint Relationship of economic optimal N rate to profile (10 ft) nitrate-N content after 30 yr of N fertilization with P. Vertical line indicates economic optimal N rate.

Phosphorus Application Constraints Limit Profitability of Sweet Corn and Lettuce Production

The economics of producing sweet corn (Zea mays L.) and head lettuce (Lactuca sativa L.) on Florida Histosols were analyzed with and without P application constraints based upon quadratic response functions derived from two experiments with each crop. At the lower end of the historical price range, production of both crops is unprofitable, especially when P is constrained. At higher prices, net returns for sweet corn under P constraints are relatively small compared with the capital invested; net returns are higher for lettuce. However, an analysis of historical monthly prices showed that those high prices rarely occur. Values for the marginal contribution of the last unit of P show that constraints greatly limit net returns. Many sweet corn and head lettuce producers may be forced out of business if P fertilization rates are arbitrarily lowered below the economic optimal rate.

Economic evaluation of replacement rates in dairy herds II. Selection of cows during the first lactation

The economic optimal rate of culling for milk production during the first lactation was studied with an extended version of a model presented by Renkema and Stelwagen (1979). Four culling policies were compared. The usual moderate culling procedure was the most profitable, the policy with no culling for milk yield being a close second. Heavy culling policies did not appear to be attractive. For a situation without genetic progress in milk production, production levels were calculated, below which, cows in first lactation with average performance in other traits should be removed from the herd. For this purpose future milk yields were estimated. These were based upon the actual milk yield of the cow, and included the probability of disposal due to ill-health at different ages, as well as correlations between partial and total milk yield of first lactation and correlations between milk yield in the completed first lactation and successive lactations. The results showed that the strongest selection should be made 2 or 3 months after calving. At that time cows producing less than about 88% of the herd level at the same age can be culled. At the end of the lactation this so-called critical milk yield decreased to about 86%. The results implied that about 20% of cows in first lactation could be culled for production. Seasonal effects may influence the critical milk yield considerably. The article was restricted to short-term aspects and did not consider any effects of the culling policy on the genetic capacity of future generations of cows. Additional calculations showed that the rate of genetic progress in a herd is affected very little by the intensity of culling for milk production