With extended drought conditions gripping Texas, Oklahoma, New Mexico and parts of Kansas, cattle feeders in the region, as well as their neighbors, are in nearly worst-case conditions for dust. In fact, it would be just about impossible under current conditions for feedyard surfaces to get any drier or more dust-prone than they already are, says a report by Brent Auvermann, a biological and ag engineer; and Ken Casey, an air quality engineer with Texas AgriLife Extension in Amarillo.
Given that the region accounts for a large percentage of the fed cattle production in the U.S., that’s a problem. In a look at feedyard dust management options authored by the two experts, they say there are four main areas that have a bearing on dust emissions:
- Uncompacted manure inventory
- Empty pen management
Here are their tips on best management practices to control dust:
Uncompacted manure inventory
The number-one priority for feedyard dust control is aggressive, careful and strategic harvesting of the uncompacted manure on the pen surfaces. This material is stirred up by hoof action or re-suspended by strong winds. Recent research using a benchtop hoof-action simulator shows the dust-emission potential of a feedyard surface is roughly proportional to the depth of uncompacted manure. The rear hoof of a steer or heifer, dragging horizontally through this material, is probably responsible for most of the dust emissions that take place during the late- afternoon and early-evening hours as animal activity increases.
- Harvesting the dry, uncompacted material can be done in either occupied or empty pens using a small tractor and a box blade, or other equipment, to collect the manure; and a front-end loader to load it into a truck or trailer in the working alley. It is best if the manure is completely removed from the pen (instead of stockpiled in the pen) so animal activity doesn’t redistribute it.
- If the manure can’t be removed from the pen, for either logistical or economic reasons, it should be moistened to about 25-30% moisture and compacted in a mound at the back of the pen.
- Because prevailing winds are from the south and southwest in the Texas Panhandle, it’s advisable to begin manure-harvesting operations on the north and northeast portions of the feedyard, unless there are good reasons to do otherwise. The downwind-most pens are most likely to contribute to nuisance conditions at nearby neighbors; the further upwind you go, the more of an effect dispersion and settling will have on neighbors’ exposure to dust.
- Finished cattle near slaughter weight, where rates of gain are low, generate more manure solids/head than just about any other group of cattle in the feedyard. Focus manure-harvesting activities on pens with finished cattle, then move on to pens with young and very active cattle, which may not have had time to accumulate a deep layer of uncompacted manure.
- Set the implement’s blade depth such that it doesn’t cut very deeply into the compacted layer beneath. The main focus is the light, dry material. Avoid cutting into the mineral soil beneath the compacted manure layer.
- In pens where the uncompacted manure is deep, box blades will fill rapidly, and manure will quickly begin to spill out the front corners. Plan your box-blade path so you can empty the box blade just as it fills. Otherwise, the pen surface will look deceptively hard and smooth, but the lines of spilled manure on either side of a box-blade path may be significant; and when you’re pulling a box blade that’s already full and spilling out the side, your time, labor and diesel fuel are all being wasted.
- Concentrate manure-harvesting activities during midday (nominally 9 a.m.-3 p.m.), when the dust emitted by machinery operations will be dispersed by turbulence from direct sunshine and higher wind speeds.
- Feedyards that have the practical option of applying water to the pen surfaces are likely to find that aggressive manure harvesting will reduce the amount of water they must apply.
- Research shows a moisture content of 20% (wet basis) is a critical threshold for controlling dust, and 25% is a critical threshold for effective compaction.
- In a year like 2011, it will be nearly impossible to apply enough water to suppress dust if uncompacted manure depths average more than about 1 in. Harvest manure as aggressively and strategically as possible before relying on water for extra dust control.
- Don’t waste water on pens with more than 1 in. of dry, uncompacted manure inventory (unless you have enough water to moisten the manure all the way through). Hoof action will penetrate the wetted crust and re-expose the dry material underneath.
- Daily evaporation rates from pen surfaces are likely to exceed ¼ in. under the current weather pattern. Focus water applications where and when they will do the most good. If it’s feasible to do so, focus water applications before each of the two critical times of day for neighbors’ dust exposure: before (6:30-8:00 a.m.) and after (5:00-6:30 p.m.) the workday – with emphasis on the early-evening period.
- As with manure harvesting, prioritize on the basis of prevailing winds. If water is limited, focus water applications on the pens on the north, northeast and east sides of the feedyard, working back to the southwest as good control is achieved.
- Run sprinkler sets longer to ensure good penetration of the water. If your sprinkler system is designed to put out 1in./day, instead of putting out 1/32 in. during each of four sprinkler cycles, put out the full 1/8 in. in one cycle, or break it into two 1/16 in. cycles, prioritizing by zones. If pen surfaces get muddy, reduce the amount of water applied or break the cycle durations in half.
- If water application is by truck, avoid wasting water on the area near the feed apron. Focus water on the back two-thirds of the pens.
- If you have electric cross-fences you can use to increase the stocking density, use them. Research indicates only a modest effect on dust concentrations, but unless you’ve observed that the cattle become more active at higher stocking densities (with buller or other aggressive behaviors), it can’t hurt to let the cattle apply drinking water in a more concentrated way by reducing the pen area to which manure and urine are excreted.
Mulching the pen surface
Preliminary research indicates some reduction in dust potential from the pen surface can be attained by applying mulches such as crop residues. Understandably, in years of drought such as 2011, the availability and feasibility of mulches will be minimal. Consideration should also be given to the additional volume of biomass that will be added to the manure, which will eventually need to be collected and removed from the pen.
Mulches, especially crop residues like gin trash, hay or straw, may reduce dust potential in two ways. First, they reduce evaporation and increase moisture retention in the manure below the mulch. Second, they dissipate or cushion the animals’ hoof action, absorbing some of the mechanical energy that would otherwise lift dust particles into the air.
Unfortunately, they also increase the volume and mass of manure that must be handled, harvested, stored and land-applied. But benchtop hoof-action simulators have shown that crop-residue mulches like hay and straw can be effective at reducing dust potential when applied to a pen surface at sufficient rates. During those benchtop simulations, waste hay applications at about 7.5 lbs./head reduced dust potential by 45%, but it’s not yet known how long that effect persists.
Management of empty pens
Although most of the nuisance conditions associated with feedyard dust are associated with the evening dust peak, strong winds at any time of day – especially the hot, dry afternoon – may generate nuisance dust events via wind “scouring,” the functional equivalent of wind erosion from open fields. The mechanisms are essentially the same: above some threshold of wind speed, which will be lower for the lighter manure particles than for mineral soils, the scouring effect will increase with wind speed.
As with cropland, then, the primary management practice is to increase the effective roughness of the surface, which will reduce the wind speed at that surface. Thus, cotton farmers will plant and then terminate wheat, or deep-plow their fields, to reduce wind speeds at the soil surface and thereby reduce soil erosion.
By the same token, when present at a sufficient stocking density, cattle themselves serve as a form of surface roughness, reducing the effective wind speed at the pen surface. Reducing wind-scoured dust emissions from empty feedyard pens implies the following management practices:
- Harvest manure from pen surfaces as soon as practical after cattle are shipped, especially if the pen won’t be repopulated for some period. Without cattle in the pen, the uncompacted manure layer is more vulnerable to wind erosion without constant moisture input from urine and progressive compaction from cattle hooves.
- Prioritizing for both manure-harvesting and stocking decisions, give particular focus to empty pens that are more exposed to the wind. This includes rows on the outer edge of the feedyard, pens on ends of rows, and pens where feed alleys are parallel to prevailing winds. If feasible within the feedyard’s management strategy, it may be best to keep these pens populated in preference to pens in the center of the feedyard if the yard isn’t full.
To read the complete report, go to amarillo.tamu.edu/files/2011/01/SP417.pdf.