Biosystems & Agricultural Engineering

2022 Grain Updates

UK Calculator for Stored Grain Capacity, Bin Sub-floor Volume and Wall Area

by Dr. Sam McNeill, Extension Agricultural Engineer

As corn and soybean harvest approach, stored grain managers on farms, elevators, and warehouses are preparing different types of structures for service. This may include applying approved insecticides or grain protectants to guard against damage caused by insects during storage. The recommended rate for most stored product protectants is based on either the volume of grain (bushels) or void space (cubic feet), or surface area of the grain or structure (square feet) to be treated. The UK storage volume calculator has always included tables that show the capacity (in bushels) of conventional round bins, horizontal storage structures (such as machinery sheds and warehouses), large round piles/rings, grain bags and corn cribs. It now includes a new worksheet to calculate the surface area of bin walls and grain piles, as well as the volume of the space below perforated floors and air space above the grain surface. A few examples are shown in the tables below for illustration and more combinations are available at https://www.uky.edu/bae/grain-and-energy-calculators.

Table 1. Storage capacity (bushels) of round grain bins.

Table 2. Wall area (ft²) of round grain bins.

Table 3. Volume (ft³) of the space below perforated floors in round grain bins.

Grain Storage Capacity of Structures+surface area +sub-floor volume v2.xlsx

Corn Harvest Losses vs Drying Costs_2022.xlsx

2022 Decision Tool Updates for Grains

Equilibrium Moisture Content for Grains¹

Moisture exchange between grain and the surrounding air is driven by differences in vapor pressure. An equilibrium state is reached when there is no net exchange of water vapor between the grain and air. This has important implications in grain drying and storage systems. As air is warmed, the relative humidity is reduced along with grain moisture (drying process). When dry grain is placed in storage and cooled, grain moisture remains constant and the relative humidity of the air surrounding it is lower.

Equilibrium moisture properties have been determined for different grains and are reported as a Standard by the American Society of Agricultural and Biological Engineers. In general, mold growth is suppressed during storage when the environment is maintained at a relative humidity level of 65% or lower, and insects are suppressed at temperatures below 60 F.

Implications for drying – Grain will reach the moisture levels shown in the tables when exposed to the corresponding temperature and humidity levels for a sufficient period of time, which depends primarily on temperature and airflow. This can occur in the field or a bin. In a bin, drying time will depend on the airflow rate through grain, which in turn depends on the depth of grain. The minimum drying rate for natural air drying is 1 cfm/bu, but this can take up to a month to dry the top layer depending on the grain and air conditions--during which time spoilage can occur.

Implications for storage – The stagnant air space between grain kernels in a bin or bag will have the humidity indicated at the corresponding moisture and temperature. For example, 15% corn at 60 degrees will generate a relative humidity in the air space between kernels of 70%, but when cooled to 45 degrees will have a relative humidity of 65% (Table 1). Similar data for soybean, soft red winter wheat and grain sorghum (milo) are shown in Tables 2-4, respectively. Additionally, a new calculator is available for twelve other grains and oilseeds that are grown in Kentucky, as shown in Table 5.

Table 1. Equilibrium moisture content of yellow corn (%wb) at different temperature and relative humidity levels.

Source: ASAE Data D245.4 / Average of two prediction equations.

¹Prepared by: Sam McNeill, PhD, PE, Extension Agricultural Engineer, UK Research and Education Center, Princeton, KY. 42445-0469,Ph: 859-562-1326,Email: sam.mcneill@uky.edu,
Web: www.uky.edu/bae/ext/grain-and-energy-calculators

Table 2. Equilibrium moisture content of soybeans (%wb) at different temperature and relative humidity levels.

Table 3. Equilibrium moisture content of soft red winter wheat (%wb) at different temperature and relative humidity levels.

Table 3. Equilibrium moisture content of grain sorghum (%wb) at different temperature and relative humidity levels.

Similar tables for barley, canola, chickpea, ear corn, millet, oats, peanuts, popcorn, rough rice, rye, and hard red winter wheat and white corn are available at: www.uky.edu/bae/ext/grain-and-energy-calculators

Table 5. Equilibrium moisture content (EMC) of various grains and oilseeds grown in Kentucky for average ambient conditions in September.

EMC for 16 KY crops_Aug 2022_SM protected_F.xlsx

Consider Drying the Remaining Corn Crop with Heated Air

Sam McNeill, Extension Agricultural Engineer

October 7, 2021

Accompanying Decision Tool for Corn Drying

Pre-harvest estimates pegged this year’s corn crop as the largest on record (~268 million bushels) but the harvest got off to a slow start. One reason was because warm temperatures in early September favored field drying, but another was due to high LP gas prices. However, since then energy prices have increased, and sporadic rains have delayed harvest, which will likely increase harvest losses. The combination certainly has the potential to squeeze profits, especially if weather further delays progress and harvest losses climb above the average of 5%.

As of this writing (Oct. 4), corn harvest has progressed to 50% complete statewide, which is well behind this time last year and the 5-year average (~65%). On a positive note, field drying should have good potential across most of the state for the next week (Figure 1), so many farmers will likely ramp up harvest and benefit from lower drying costs.

Figure 1. Equilibrium moisture trend for corn in Mayfield (solid line), Madisonville (dotted line) and Elizabethtown/Lexington (dashed line) from Oct. 4 to 11 based on predicted ambient conditions. Source: Clemson EMC Calculator

CONSIDER THE AVERAGES: This year’s anticipated statewide yield for Kentucky (186 bu/ac), current price ($5.00/bushel), and corn harvest losses (5%) amounts to $47 per acre. Harvest losses can be held to 2% by attentive combine operators, few or no weeds and down stalks in the field, and good weather conditions, so the cost of leaving some of the crop in the field can be reduced to $19 per acre if other average conditions hold. On the flip side, excessive wind and/or rain plus weak/down stalks can increase harvest losses to 8%, or $74 per acre.

CONSIDER HEATED AIR DRYING WHERE POSSIBLE: Compare these costs to heated air drying, which depends on fuel cost (LP or natural gas), harvest moisture, and the energy efficiency of the dryer. An average drying efficiency for many new dryers is between 1500 and 2000 Btu/lb of water, so again I’ll use an average (1750 Btu/lb) in the examples shown in Table 1. If LP costs $1.90 per gallon, the cost to dry corn to 15 per cent moisture from harvest levels of 25 and 20 percent for the drying energy alone would be $54, and $32 per acre, respectively. Another $7 per acre can be added to include labor, extra hauling and depreciation on the dryer. This range of values is anticipated this season, but producers can use their own values to quickly estimate a meaningful comparison for their operation. The table below illustrates the costs per acre for a typical range of yields and anticipated harvest losses for the corn and fuel prices shown. Returns to drying are calculated for the energy costs alone (assuming the dryer has been paid for) and for ownership costs (which includes drying energy, repairs, labor, and hauling costs).

BOTTOM LINE: Most operations have average harvest losses. This comparison favors drying 5 points of drying at all yield levels even with this season’s high energy prices. The value and satisfaction of knowing the crop is safely out of the field depends on individual operations and should be added to the costs shown in Table 1. 

Table 1. Corn drying costs ($/ac) for three yield levels for 5 and 10 points of moisture removal. A drying efficiency of 1750 Btus per pound of water is assumed along with an LP gas price of $1.90 per gallon to calculate energy costs alone (assumes the dryer is paid for) and total cost (includes energy, labor, depreciation and hauling).

Table 2. Return costs to heated air drying ($/ac) for different yield and harvest loss levels with $5 corn and two drying levels (5 and 10 points). Numbers shown in parentheses represent negative values.

Timely Soybean Planting is Pivotal to Profits

Sam McNeill, Extension Agricultural Engineer

sam.mcneill@uky.edu

Soybean Harvest Drying and Storage - Fall 2017 (PDF)

Mild weather and concern for delayed planting of double crop soybeans provides motivation to consider harvesting wheat a bit earlier this spring and drying the crop when possible. Harvest moisture is dictated by the available drying system, with 15%, 17% and 20% or higher suggested for bins without heat, bins with heat, and high temperature dryers, respectively, A recent survey of cash prices for wheat and soybeans showed current levels near $5 and $9 per bushel, respectively. Current energy prices are similar to last fall, with LP gas around $1.40 per gallon. 

A spreadsheet was developed to help producers weigh the costs of wheat drying with the probable loss in soybean yields due to delayed planting. It considers grain and energy prices along with a few other related factors that are then used to calculate gross profits from the soybean crop and net returns to the wheat enterprise after subtracting drying and handling costs. Potential yield losses per day are considered also for both crops. For wheat, a field drying rate is assumed to calculate the drying cost as harvest progresses. Of course, towards the end of harvest, wheat will usually be dry enough to store or market directly from the field but may result in over-drying which is an additional cost. By that time potential soybean yields will have fallen off dramatically.

To look at an example, consider the ‘pivotal’ harvest date where potential soybean yields reach a break point. This varies from year to year depending on available heat units or degree days for crop development. You would want to start harvest several days earlier to avoid working much beyond that date and allow for harvest capacity and a few delays due to weather and/or mechanical problems. With current grain prices, a soybean yield of 45 bushels per acre, and daily yield loss of 2.3% (1 bushel per acre per day), the costs of delayed planting can be calculated. For wheat, an average yield of 85 bushels per acre with a 0.5% loss per day for delayed harvest can be assumed. Drying costs will vary between systems, but with current energy prices and an initial moisture level of 26%, the drying and handling cost would be about 26 cents per bushel (or $22 per acre). The gross return for soybeans and net return for wheat after paying for drying and handling (D & H) would be $405 and $403, respectively (Table 1) when high temperature drying is available to allow harvest to begin one week before the ‘pivot’ harvest date (week -1).

Table 1.  Changes in soybean and wheat yields, wheat drying costs, and returns to the double crop enterprise during a 3-week harvest period with no extreme weather losses.

* Returns assuming a double crop production cost of $600/ac.

To be profitable, this total must cover production costs for double crop enterprises, which vary widely but were estimated to be $600 per acre this year by UK’s Agricultural Economics Department (https://anr.ca.uky.edu/content/decision-aids-budgets-calculators). This value includes machinery costs but not land rent, but this can easily be added for individual operations. Table 1 shows that a profit of $208/ac could be expected when harvesting wheat a week before the ‘pivot’ date. Each row in the table shows how these costs and returns change through a 3-week harvest period. Note that if harvest is delayed two weeks beyond the ideal period, returns to the operation can fall sharply due primarily to lower potential soybean yields and over-drying cost if wheat dries in the field below the market moisture level (usually 13.5%).
Data in the table are shown in more detail in Figure 1, where daily changes in soybean and wheat yield losses, wheat drying and handling, and the total of these costs are illustrated. Corresponding net returns for the double crop enterprise (last column in Table 1) show an average about $2.4 per acre-day before the ‘pivot’ harvest date (due to wheat drying) and increase to about $11 per acre for each day that soybean planting is delayed afterward (due to lower yields)! For these reasons, farmers who have dryers will be interested in harvesting wheat early this spring to boost soybean yields and net profits. 
More information on wheat drying is provided in Chapter 10 of UK’s Wheat Management Guide (http://ww2.ca.uky.edu/agcomm/pubs/id/id125/10.pdf) and at UK Cooperative Extension Service offices, The spreadsheet is available on the Biosystems and Agricultural Engineering website (www.uky.edu/bae) or by contacting the author.
Fig. 1. Daily operating costs for drying wheat and planting soybeans early compared with field drying and delayed planting using current prices ($9.00 for beans, $5.00 for wheat and $1.40 for LP gas).