How to Increase Oat Grain Size and Weight

Oat grain size is determined by the plants genetics i.e. variety, and the length of the grain filling period.

As soon as pollination has occurred the embryo and endosperm begin to develop with the plant redirecting photosynthates and also previously stored starch and protein (in leaves and stems) to these developing grains. The longer this period of grain fill is, the larger oat grain size is likely to be. Besides nutrient management, the grain size can be influenced by water management (irrigation to avoid drought stress), as well as disease management – use fungicides and nutrients to maintain green leaf area and reduce disease incidence improving plant health.

Crop Nutrition and Oat Grain Size and Weight in Oats


Effect of nitrogen timing on grain weight in spring oats

Nitrogen management will have the most impact on final oat grain size and weight. Applications made early will ensure a canopy that is large, containing high levels of stem carbohydrate that is translocated to the developing grain during maturation. This is particularly important in drought areas where 60% of the grain yield could come from this store. It is important to monitor plant nitrogen levels ensuring the canopy does not senesce early and curtail the grain filling period. Later nitrogen applications increase the grain weight.


Phosphate has a major role in the supply of energy for plant processes. Redistribution of stored carbohydrate requires energy making phosphate nutrition important in achieving good oat grain size. Both solid fertilizer phosphate and foliar phosphate can be used to improve final grain size.


Potassium aids movement of nutrients around the plant as it regulates the transpiration flows as the oat plant redistributes minerals to the ear potassium levels need to be maintained. Potassium will also help avoid early senescence often brought on by drought during grain fill. Potassium deficient plants are poor at regulating transpiration through the leaf leading to heat stress and wilting. Adequate potassium supplies will extend the grain filling period leading to improvements in oat grain weight.

Manganese and Zinc 

Both manganese and zinc with their roles in nitrogen metabolism by the plant, will improve oat grain weight.

Other Crop Management Practices Increasing Grain Size and Weight in Oats

  • Plant protection 
  • Weeds control 
  • Pest management, especially aphids. 
  • Disease management especially the rusts and Fusarium.

Harvesting, drying and storing 

Full ripening is especially important for hulled oat. To maintain crop quality the grain or the husk must not be damaged during threshing. Oats must be free of weeds and other foreign particles and substances. Drying should be started as soon as possible after threshing. Excessive heat should be avoided in drying hulled oat as it may damage the core of the grain. Oat is dried to less than 14% moisture content.

Soil and pH management 

The soil quality requirements for oats are less demanding than those of wheat and barley. Only rye is less demanding than oats. Most reasonably fertile and dry soils suit oats if the temperature and moisture conditions are favourable. 

The soil nutrient requirements (N, P, K) of oats are slightly less demanding than those of wheat, barley and corn. Oats are considerably more susceptible to salt concentration than barley and slightly more susceptible than wheat and rye.

Oat varieties tolerate the acidity of the soil better than other cereals. Oats have been found to tolerate even 4.5 pH, but to reach maximum yields, the field needs to be limed to a pH level of 5.3-5.7.

Later nitrogen applications increase the grain weight.