Primary symptoms

Optimum density varies with variety and growing conditions, but you do want from 170-220 plants per sq m established.

Summary

Numbers of plants in a crop depends on seed rate, seed viability, percentage seedling emergence and plant survival. However, plant numbers can often vary widely without appreciably affecting yield in irrigated crops. This is because wheat plants produce tillers, which themselves can produce leaves, spikes and grain. So seed rate is commonly less critical to final yield than many of the other factors dealt with in this section.

For example, in a study from Sudan, yields did not change much over a 15-fold range of seed rate, because at low seed rates each plant produced more tillers and spikes. But note that final yields were also not very high.

Recommendations for seed rates are usually between 100-150 kg/ha, which is higher than necessary but allows for losses due to poor preparation of seed beds, poor seed, and poor distribution of seed as occurs with hand broadcasting. Very high plant populations can encourage disease (Du Daiwen 1994) but do reduce the effects of weeds by competing better, a more important consideration in some areas. Some consider that very high seed rates lead to a higher chance of lodging.