Crop species, such as maize, soyabeans, wheat and sorghum, are quite far advanced in terms of domestication. Part of the domestication process is that the crop is selected and bred to emerge all at once. In a mono-cropping situation this has some distinct advantages. Early emerging plants don't have to compete with late comers for sunlight, water and nutrition. They also mature uniformly, enabling easy harvesting. You must appreciate that it has taken thousands of years to get those species to this point.

Conversely, pasture species, and especially tropical grasses are still very primitive and often genetically variable. The main issue is DORMANCY, which is actually quite advantageous in a pasture situation. Moisture is often unreliable and dormancy allows for retention of a portion of the seed until more favourable conditions arise. In some species and places this can be years apart.

The other problem is that there is often a much lower viability in grasses than crops. This is because there is a wide spread of flowering and it is simply impossible to harvest all seed at the optimal time. Some will be very mature to the point of shattering while others will have only just pollinated. There is no easy way around that. Grass seed is also much more difficult to grade than crop seed, which is more dense and of course larger.

Legume seeds can present a different problem - hard seed. This is a form of dormancy that is overcome over time or may be overcome through scarification or sometimes by soil conditions.

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