Summary

An economic model was developed to evaluate cost and value of manure distribution. A 2,500 head feedlot was used as a case study to calculate excretion amounts from cattle fed diets with a range of phosphorus. Diet P and subsequent costs of distributing that manure were used to analyze the corresponding costs of manure P distribution, in addition to determining the required acres needed to be in compliance with a nutrient management plan (NMP) based on use of manure P by the crops grown. The model illustrated when animals are fed diets of increasing P concentration, total distribution cost increased, ranging from $2.80 - $5.10/head finished/year, but the agronomic and market value of manure produced increased at a rate faster than the rate of increasing costs of distribution for a small feedlot.

Introduction

Implementation of P management, as required by environmental regulation, will continue to present unique challenges to beef feedlots. Recent work (2006 Nebraska Beef Cattle Report, pp 94-97) suggests the amount of P harvested in manure from beef feedlots varies with 1) level of P in the diets 2) individual pen conditions prior to and at time of manure harvesting, and 3) requirements for use of manure solids for surface maintenance prior to harvesting. These data indicated a positive correlation between P intake and P in harvested manure in beef feeding operations. In addition, previous data (2005 Nebraska Beef Cattle Report, pp51-53.) suggested P excretion is positively correlated to P intake. It is important that correct estimates of P excretion are used by producers if NMPs are based on use of manure P.

Costs of manure P transport and distribution are critical information, but information is limited. The savings from least cost rations based on a corn processing by-product may be offset by the additional cost of handling manure P. An economic model that reflects P excretion from P intake and retention for individual operations can assist in development of NMPs for feedlots. Thus, the important objective of our project was to develop an economic analysis for proper distribution of manure P relative to dietary P and agronomic use in various crop rotations.

Procedure

Software Model Development

An economic model was developed to calculate nutrient excretion amounts from cattle fed diets with a variable range of P, and analyze the corresponding costs of manure P distribution. Software development incorporated appropriate features from existing models, previously developed by researchers at University of Nebraska and University of Missouri, for calculation of nutrient excretion amounts and analysis of manure distribution cost, respectively.

Equations used in the model were based upon the revised ASAE Standard D384.2, Manure Production and Characteristics. Nutrient intake was calculated using dietary nutrient concentration of each diet fed multiplied by DMI. Cattle nutrient retention was calculated according to the retained energy and protein equations established by the National Research Council (1996) for beef cattle. Equations used for beef excretion characteristics were based upon a calculation of dietary intake minus animal retention, the approach used by the ASAE nutrient excretion standard.

Model Data Input Variables

The software is designed to have flexibility of application of input variables. Table 1 shows values assumed in the model as constants, which can be changed if desired. The model allows the user to enter farm specific information such as average starting and finishing weights, average days on feed, feedlot capacity and turns of cattle/ year; diet nutrient concentration; manure handling equipment values and capacities utilizing truck or tractor spreading equipment; fuel prices, fertilizer nutrient market values; loading time, travel speed, and spreading calibrations; various crop rotations; and, land available for distribution of manure nutrients, distance from the feeding operation, and crop removal rates of nutrients based upon crop and yield.

Case Study Feedlot Scenario

A case study was designed to help define the economic issues associated with feeding dietary P, and the costs of distributing manure on a P basis. In our case study, a theoretical 2,500 head one-time capacity feedlot, averaging 750 lb in weight and 1250 lb finish weight in 153 days, with two turns of cattle per year, was used to quantify the manure and nutrients harvested from cattle fed various combinations of diet P and CP. Multiple situational scenarios were identified for analysis of the economics of distribution of manure P harvested from cattle fed diets with a range from 0.29-0.49 % P (DM basis), illustrating a range from a corn and forage base diet, to diets with 10%, 20%, 30%, and 40% corn replacement with by-product from ethanol production. Analyses were performed increasing the diet % CP and % P concurrently as by-product % increased. In addition, scenarios were developed for 2- and 4-year application rates for P with various CP and diet P levels. All of these variables were compared for continuous corn (CC) and corn-soybean (C-SB) crop rotations to analyze the crop rotation effect.

Case Study Feedlot Scenario

Based on the average values from previous studies (2006 Nebraska Beef Cattle Report, pp. 94-97), the model calculates annual manure production, and after accounting for open lot or feedlot scraped or stockpiled storage losses, manure nutrient concentration is determined.

Crop Removal Value of Manure Nutrients

With the total N, P₂O₅, and K₂O lb/ton of manure determined, the manure application rate is calculated based upon the nutrient use of the desired crop in the specified rotation. In this study, for total N, the NH₄-N to organic N ratio was set at 0.20:0.80, and it was assumed that no NH₄-N would be available to the crop. The reasoning was the assumption, in most cases the manure would not be incorporated soon after surface application and any remaining NH₄-N would be lost. Fifty percent of the organic N is credited for crop use for continuous corn and 32% for corn-soybeans. The model has the flexibility to determine manure application rates, on either P basis or N basis, as a function of nutrient concentration of the manure and nutrient removal rates (Table 1) for the specific crop yield of the specific crop grown. No nitrogen credit was given when applied to legumes; the only N value was credited for removal by growing corn.

Spreadable Acres Needed

The spreadable acres needed to use the annual manure produced were calculated from the annual manure produced divided by the average manure application rate for the rotation crops. This information is needed in a NMP. The model did not incorporate the cost of additional land ownership, or expenses related to control of added land for manure distribution.

Average Distance to Fields

For simplicity, the assumption in this case study was that all land nearby the feeding operation was available for manure application. Thus, the average distance to fields is relatively low in the scenarios investigated. In reality, this may not be the case, but the model has the capability to adapt to individual field locations available for manure application for each individual feedlot. Likely, at most, only half the land would be available. This is easy to adjust in the model by increasing the average distance to fields variable. Doing so will increase the costs of distribution, and the results will be more conservative.

Equipment Ownership and Operating Costs

The model tracts the equipment ownership and operating costs (Table 1) relative to value of the tractor(s), or truck chassis(s), and spreader(s), years to replace, salvage value, depreciation, interest, insurance, repair, and costs of fuel and labor. In addition, equipment capacities and swath width, road travel time, field travel time, total loaded miles, and total road miles are variables which affect costs of transporting and distributing manure.

Costs of Distribution: Costs of Transporting and Spreading Manure

When the farm specific amount of manure P has been established for the individual diet P concentration used in an individual beef feedlot, and the equipment ownership and operating costs have been determined, the model is intended to be used by feedlot operators to estimate the cost of distributing the resultant manure P on land. For individual feeding operations, the costs of scraping the pens, storage, and loading the manure remain constant, regardless the P concentration in the manure. Thus, those costs were not included in this study and this model. As the manure P concentration varies, the other variables in the model are distance required to transport the manure, and the necessary spreading of the manure to be in compliance with a NMP based on use of manure P by the crops grown. In this model, cost of transport plus cost of spreading, together are defined as cost of distribution. The output is the variation in cost of distribution of manure P as a result of variation in diet P concentration. The value of the manure minus the cost of distribution equals the net manure value, as a function of diet P concentration. In addition, the cost of distribution per animal fed annually is determined.

Results

In all scenarios in this case study (Tables 2, 3, and 4), as the spreadable P manure concentration increased as a result of increased diet P concentration, the manure application rate decreased and the spreadable acres required for all crop rotations increased. Correspondingly, the total application time and average distance to the fields increased as diet P concentration increased. The downside of these factors was the resultant increase in total cost to distribute the manure. This ranged from a low cost (Table 3) of $14,000 for the four-year continuous corn scenario with 0% by-product to a high cost (Table 2) of $25,100 for the two-year corn-soybean rotation with 40% by-product in the diet. A feedlot will need to have access to increased land (up to 90%) and additional labor (increase by 45 to 65%) to meet the increased requirements for manure application to manage the additional P. On the positive side, high P diet increased the fertilizer value of manure faster than it increased the cost of distribution. In the case study scenarios in this report, the annual net market value of manure (Table 7) increased in all cases as the P concentration of the diet increased.

Tables 5, and 6 summarized the comparison of annual total fertilizer value and phosphorus value, respectively, by crop and variation in diet CP and P. There is little difference in fertilizer values when comparing 2-year to 4-year P application rates. Likewise, the cost comparison between 2-year and 4-year P application rates change a little, but not a lot, with slightly more expense in the 2-year than the 4-year. The surprise is the increase in net manure value as the diet P concentration increases.

An interesting bench mark is the cost per animal finished per year, calculated as total cost of distribution divided by total animals finished per year (Tables 2, 3, and 4). These values ranged from $2.80/head finished/year in Table 3 for continuous corn with 0.29% P and 4-year P rate, to a high value of $5.10/head finished/year in Table 2 for C-SB at 0.49% P and 2- year P basis application rate.

Another interesting perspective is to compare these scenarios on the basis of net value of manure per animal finished per year. If a true fertilizer market value is placed on the manure and the cost of distribution of the manure is evaluated, then the net manure value per head can be determined by the model. For instance, from the case study data (Tables 2, 3, and 4), this value calculated from a low of $2.60/head (Table 4) to a high of $7.70/head (Table 3) for net manure value per annually finished animal.

In conclusion, the model illustrated that when animals are fed diets of increasing P concentration, there are positive and negative aspects. On the downside, there was an increase in application time (Tables 2, 3, and 4) and required spreadable acres (Table 8) receiving the increasing P manure concentrations, due to the decreasing rates of manure application. On the upside, the agronomic and market value of manure produced increased at a rate faster than the rate of increasing costs of distribution. This has a potential positive implication to the beef cattle industry, with the 2500 capacity feedlot in this study. Further scenarios need to be investigated with different sized feedlots, and available fields for manure distribution at much greater distances from the feedlot. This model has the ability to investigate such individual feedlot situations.

In this case study, from the perspective of cost of distribution/head finished/year, lower diet P concentration is better than higher diet P values. However, due to the fertilizer value, increased diet P results in higher manure value. This higher manure value offsets the distribution cost by a range of $2.60/head to $7.70/head finished annually in the scenarios studied in this model. As higher diet P concentrations from feeding increasing amounts of by-products from ethanol production result in higher manure P concentrations, it is potentially beneficial to distribute the higher value manure in compliance with the nutrient management plan.