Dorothea McKeller, wrote “I love a sunburnt country, a land of sweeping plains, of ragged mountain ranges, of droughts, and flooding rains.”
As many farmers know, we are at the mercy of Australia’s ever changing sometimes brutal weather conditions that make up our climate. Many years of drought, fire and flooding rains have battered our pastoral areas that are dominated by C4 tropical grasses. Buffel, Rhodes Grass, Panic, Setaria, and Bluegrasses are all C4 plants. This term refers to the pathway the plant uses to capture carbon dioxide during photosynthesis. The C4 pathway evolved in species in the wet and dry tropics.
C4 plants evolved in and are adapted to warm or hot seasonal conditions, under moist or dry environments. C4 grasses tend to be less frost tolerant compared with C3 species, and they generate more bulk which leads to more feed through the growing season.
Features of C4 Grasses compared to C3 Grasses| C3 carbon pathway | Requirements | C4 carbon pathway |
|---|
| Cool season or year long | Growth period | Warms Season |
| Lower | Light requirement | Higher |
| Lower | Temperature requirement | Higher |
| Higher | Moisture requirement | Lower |
| Higher | Frost tolerant | Lower |
| Higher | Feed Quality | Lower |
| Lower | Production | Higher |
With the climate anomalies being experienced by farmers in tropical regions, there have been some seed production issues. Seed viability has been lower than usual. This has been caused by cooler than normal temperatures affecting where the plant places its energy. Tropical grasses will put a lot of energy into plant growth leading to very bulky plants which is great for feed production but in turn less energy is placed into the production of seed for the next generation.
Wet conditions during flowering, especially for grasses is detrimental. Tropical grasses are often self-pollinating, and pollen is extremely light, so can be easily dislodged from the floret during periods of rain, leading to a higher proportion of un-pollinated seed.
Tropical grasses require a significant amount of light for both development of foliage and seed. Insufficient sunlight caused by a greater frequency of cloudy days during growth and development, forces the plant to place most of its energy into keeping the vegetative parts of the plant, and therefore less energy into seed production. The inflorescence may then produce numerous seeds but with differing rates of maturity.
All these factors will be seen during the testing of seeds in the laboratory. Farmers and seed companies will likely see reduced germination rates and viability (Tetrazolium test) on their seed analysis certificates.
The AgEtal Team
