Justin Waggoner, Ph.D., Beef Systems Specialist, Garden City
Cattle producers often utilize crop residues such as wheat straw to sustain cows during drought conditions. However, the use of these forages is often limited by their low nutrient content and digestibility. The feeding value (crude protein, and dry matter digestibility) of straw may be enhanced by treating straw with anhydrous ammonia. Traditionally, a 3% application of anhydrous ammonia (dry weight) has been recommended (60 lbs anhydrous ammonia/dry ton hay). However, research conducted a K-State demonstrated that lower application rates (1.5% dry weight or 30lbs anhydrous ammonia/dry ton hay) produced proportionally greater improvements in both crude protein and in-vitro dry matter digestibility. The results of this study are summarized in the table below and the full report may be accessed online in the 2014 K-State Cattleman’s Day report http://hdl.handle.net/2097/17779.
Nutrient composition and estimated cost/value of wheat straw prior to (PRE) and following application of 1.5% or 3.0% anhydrous ammonia on a dry basis.
| Ammonia Rate1 | |||||||
| Item | PRE | 1.5% | 3.0% | SEM | P -value | ||
| Dry Matter, % | 92.1 | 91.0 | 91.1 | 1.01 | 0.68 | ||
| Crude Protein, %* | 3.3a | 8.6b | 10.8c | 0.50 | < 0.01 | ||
| Acid Detergent Fiber, % | 51.0 | 51.9 | 52.1 | 1.34 | 0.84 | ||
| TDN, % | 33.2 | 32.5 | 32.3 | 1.90 | 0.93 | ||
| IVDMD, %† | 31.0a | 42.0b | 46.2c | 1.60 | < 0.01 | ||
| Cost/value, $/ton | 70.00 | 107.00 | 128.00 | ||||
1Treatment with 1.5% (HALF) or 3.0% (FULL) dry weight basis of anhydrous ammonia.
*Linear P < 0.01, Quadratic P = 0.02
a,b,c, Within a row, means without a common superscript differ (P ≤ 0.10)
† Linear P < 0.01, Quadratic P = 0.10
The 1.5% application of anhydrous ammonia yielded a 35% improvement in digestibility (IVDMD) whereas the 3.0% application resulted in a 49% improvement. Although the 3.0% application rate did yield a greater improvement in digestibility it only improved IVDMD% by 4.0 units.
Additionally, producers should also be advised that the costs associated with ammoniating wheat straw have increased. A 40 x 100-foot roll of 6 mil black plastic will cost approximately $325 and anhydrous ammonia is currently $1400/ton in some locations. At these prices the cost/value of wheat straw treated with the 1.5% and 3.0% application rates is $107 to $128/ton respectively. At these values producers should evaluate what other forage options are available before making the decision to ammoniate wheat straw as other comparable, cost-effective forage options, such as grass hay, may be available.
