Explanation:

 Commercial grain farming is an extensive and mechanised form of agriculture. This is a development in the continental lands of the mid-latitudes, which were once roamed by nomadic herdsmen.
Characteristics:
(i) Specialisation in single crop:
Commercial grain farming is highly specialised and generally one single crop is grown. In most commercial grain regions that crop is wheat. Both winter wheat and spring wheat is grown in these areas.
(ii) Farms are very large:
The wheat farms in mid-latitudes are very large, ranging from 240 to 16,000 hectares. Though average size of the farm in the USA is about 400 hectares. In these areas land is cheap that makes it possible for a farmer to own very large holdings.
(iii) Highly mechanised:
The commercial grain farming is highly mechanised. Cultivation from ploughing to harvesting is often entirely mechanised. The use of tractors ploughs drills and combines harvests which reap, thresh, winnow and sack the grain all in one operation is common.
(iv) Low yield per acre but high yield per man:
In this farming wheat grown gives comparatively low yields. The average yield is seldom more than 1,700 kg per hectare, whereas under intensive cultivation the yield is more in many countries. But because of mechanisation, less labour force is required; therefore, yield per man is high.
Other features of the commercial grain farming are:
(a) Lack of irrigation
(b) Farm ownership