Sorghum and Sudangrass: Drought-Tolerant Forage Crops for Cattle Farms
Corn is the ideal silage crop when conditions allow it. But corn is also thirsty, temperature-sensitive, and expensive to establish. In the hot, water-limited conditions that occur across Uzbekistan's southern provinces — and during dry years everywhere — corn yields can drop sharply or fail outright. Sorghum and sudangrass fill this gap. They produce substantial biomass under conditions that would leave a corn field stunted, and their role as "insurance crops" in a well-planned forage program deserves serious consideration by every cattle farmer in the region.
Understanding the Sorghum Family
Sorghum (Sorghum bicolor) has been cultivated for thousands of years in arid and semi-arid regions. For cattle feeding, the relevant types are:
Forage/sweet sorghum — grown primarily for green mass or silage. The tall, cane-like stems accumulate sugars (especially sweet sorghum types) and yield large volumes of fermentable biomass.
Grain sorghum — shorter, grown for the seed. The grain can substitute for corn or barley as a concentrate feed, though with some differences in rumen handling.
Sudangrass (Sorghum sudanense) — a finer-stemmed, multi-tillering species closely related to sorghum. Grows quickly, regrows well after cutting, and suits green-chop or multi-cut silage systems.
Sorghum-sudangrass hybrids (forage sorghum × sudangrass) — combine high biomass from sorghum with the regrowth ability of sudangrass. BMR (brown midrib) versions of these hybrids have lower lignin, significantly improving digestibility.
Source: University of Nebraska-Lincoln, Sorghum Production Guide, 2023
How Sorghum Compares to Corn Silage
| Parameter | Corn Silage | Sorghum Silage |
|---|---|---|
| Water requirement (mm/season) | 500–700 | 350–450 |
| Heat tolerance | Moderate | High |
| NEL — Net Energy for Lactation | High | Moderate |
| Starch content (DM basis) | 30–35% | 10–15% |
| NDF (fiber content) | 40–50% | 50–60% |
| Crude protein (DM basis) | 7–9% | 7–12% |
| Green mass yield (t/ha) | 40–60 | 35–55 |
| Drought tolerance | Low | High |
The main trade-off is clear: sorghum silage delivers less starch (therefore less energy) than corn silage, but it delivers this at substantially lower water cost. For farms with constrained irrigation, this is not a compromise — it is the only viable option in many years.
Source: Texas A&M AgriLife Extension, Sorghum vs. Corn Silage, 2023
Why Sorghum Matters for Uzbekistan Farmers
Southern provinces (Surkhandarya, Kashkadarya) regularly experience summer temperatures and water availability conditions that push corn to its physiological limits. In these areas, sorghum is not a fallback — it should be a planned component of the forage rotation.
Double-cropping opportunities. After corn silage is harvested in August, sorghum or sudangrass can be planted immediately into the vacated field. A late-summer sorghum crop harvested in October extends the forage season without requiring a separate field block. This is one of sorghum's most practical advantages in Uzbekistan's long growing season.
Water-use efficiency. Sorghum produces roughly 30–40% more dry matter per millimeter of irrigation water than corn. For farms paying for water by volume, this efficiency advantage has direct economic value.
Agronomic Management
Planting Date
Sorghum and sudangrass are warm-season crops with a minimum germination temperature of 15–18°C. Planting into cold soil leads to poor emergence and weak establishment.
- Primary planting: Mid-May in most of Uzbekistan (once soil warms consistently)
- Double-crop/second planting: Late July to early August, immediately after corn silage harvest
Seeding Rates
| Crop Type | Seeding Rate | Row Spacing |
|---|---|---|
| Forage/sweet sorghum (silage) | 15–20 kg/ha | 45–50 cm rows |
| Sudangrass (green chop or multi-cut silage) | 25–35 kg/ha | Broadcast or 30 cm rows |
| Sorghum-sudangrass hybrid | 10–15 kg/ha | 45–50 cm rows |
Fertilization
| Nutrient | Rate |
|---|---|
| Nitrogen (N) | 100–150 kg/ha |
| Phosphorus (P₂O₅) | 60–80 kg/ha |
| Potassium (K₂O) | 50–60 kg/ha |
Nitrogen is especially important for biomass yield. Apply 40–50% at planting and the remainder as a side-dress when the crop is 40–60 cm tall.
Harvest Timing
Sorghum Silage
Harvest when plants reach 1.5–2.0 m in height and flowering begins. At this stage, whole-plant moisture is approximately 65–70% — similar to optimal corn silage harvest moisture. The fermenting mass packs adequately and produces stable silage within 3–4 weeks.
If harvested too late (plant moisture below 60%), packing becomes difficult, air pockets form, and aerobic spoilage risk increases. If harvested too early (above 75% moisture), fermentation produces excess effluent and dry matter losses increase.
Sudangrass (Multi-Cut System)
Cut the first time when the crop is 80–100 cm tall. Allow regrowth and cut again at 80–100 cm. This multi-cut system yields 3–4 harvests per season and consistently high-quality material.
Prussic Acid (Dhurrin): A Critical Safety Issue
All sorghum family plants contain dhurrin, a cyanogenic glycoside that releases hydrogen cyanide (prussic acid / HCN) when plant cells are disrupted. In most circumstances this is not a problem with properly managed sorghum feeding. However, specific conditions dramatically increase prussic acid concentration:
- Young plants below 60 cm: Immature sorghum has the highest dhurrin concentration. Never graze or feed green-chopped sorghum that has not reached 60 cm height.
- Following frost: A freezing event ruptures cell walls throughout the plant, releasing dhurrin rapidly. After any frost, wait 4–5 days before cutting and allow the material to dry or wilt before feeding. Wilting reduces prussic acid by 50–75%.
- Drought stress: Water-stressed sorghum accumulates more dhurrin than well-watered plants.
- Regrowth after cutting: New regrowth has elevated dhurrin for the first 7–10 days.
Signs of prussic acid poisoning: Rapid breathing, bright pink mucous membranes, muscle tremors, sudden collapse. Death can occur within minutes of severe exposure. Treatment (sodium thiosulfate + sodium nitrite IV) must be administered immediately by a veterinarian.
BMR hybrids have significantly lower lignin but do NOT necessarily have lower dhurrin than standard varieties — do not assume a BMR hybrid is safe to feed at early growth stages.
Source: University of Wisconsin Extension, Prussic Acid Poisoning, 2022
Silage eliminates most prussic acid risk — the ensiling process allows dhurrin to volatilize over the fermentation period. Sorghum silage properly made and well-fermented is safe to feed to cattle without prussic acid concern.
Nutritional Value of Sorghum Silage
At milk-dough/dough stage harvest (DM basis):
| Parameter | Value |
|---|---|
| Dry matter | 28–35% |
| Crude protein | 7–10% |
| NEL (net energy for lactation) | 1.40–1.55 Mcal/kg |
| NDF | 50–58% |
| Starch | 10–18% |
| pH (post-fermentation) | 3.9–4.3 |
Compared to quality corn silage (NEL ~1.65–1.75 Mcal/kg), sorghum silage is 10–15% lower in energy. This gap is largely closed in BMR hybrids, which can approach corn silage in digestibility due to their reduced lignin content. When ration balancing with sorghum silage as the primary forage, compensate for the lower energy density with additional concentrate or by including alfalfa hay.
BMR Varieties: Closing the Quality Gap
Brown midrib (BMR) sorghum-sudangrass hybrids carry a genetic mutation that reduces lignin in the cell wall by 40–50% compared to conventional varieties. Lower lignin means:
- Higher NDF digestibility (dNDF)
- Better voluntary intake
- More net energy extracted per kilogram of silage
Studies comparing BMR sorghum silage to conventional sorghum silage consistently show improvements of 10–15% in milk production when BMR replaces conventional. In water-limited settings, BMR sorghum-sudangrass can realistically substitute for a significant portion of the corn silage fraction in a dairy ration.
FAQ
1. Can sorghum silage fully replace corn silage in a dairy ration?
In part, yes — particularly for mid-production cows and growing heifers. High-production cows (over 30 liters/day) will need energy supplementation if sorghum silage replaces a large fraction of corn silage. BMR sorghum silage handles this substitution better than conventional sorghum.
2. Is sorghum silage safe for all livestock?
Yes, when properly harvested and fermented. The main concern — prussic acid — is effectively eliminated during the ensiling process. Fresh-cut sorghum at early growth stages should not be fed directly to cattle without proper management (height above 60 cm, wilting after frost).
3. What is the yield difference between sorghum and corn silage per hectare?
Under water-limited conditions where corn struggles, sorghum often out-yields corn significantly. Under optimal conditions with adequate irrigation, corn typically produces 20–30% more dry matter per hectare. The comparison depends heavily on the specific season and water availability.
4. Can I graze sorghum or sudangrass?
Yes, but with strict height management. Never allow cattle to graze sorghum or sudangrass below 60 cm height. Rotational grazing with large paddocks works better than set-stocking. Do not allow access to frosted plants for at least 4–5 days. Sudangrass hybrids and BMR types are safer for grazing than straight sorghum.
5. How do I decide between growing corn or sorghum for silage in a given year?
The decision should be driven by your water allocation for the season. If you have full irrigation capacity, corn delivers higher energy per hectare and the choice is straightforward. If water is limited to 400–500 mm equivalent or less, sorghum will out-yield stressed corn and produce a more consistent result.
6. Can sorghum be grown as a second crop after corn silage?
Yes — this is one of sorghum's most practical applications. After corn silage harvest in late July or early August, sorghum or sudangrass can be planted immediately. With 60–70 days of growth before first frost, a second cut of 15–25 tonnes fresh mass per hectare is achievable in most Uzbekistan provinces.
7. Does FarmOps track which forage lots came from sorghum versus corn?
Yes. FarmOps allows farmers to log forage inventory by source crop and quality test results. When multiple silage types are in use, this tracking is essential for accurate ration formulation and feed cost calculations.
Sources and References
- University of Nebraska-Lincoln. Sorghum Production Guide. 2023. extension.unl.edu
- Texas A&M AgriLife Extension. Sorghum vs. Corn Silage Comparison. 2023. agrilifeextension.tamu.edu
- University of Wisconsin Extension. Prussic Acid Poisoning. 2022. extension.wisc.edu
- FAO. Sorghum and Millets in Human and Animal Nutrition. 2022. fao.org