Nitrogen, phosphorus, and potassium fertility requirements for optimizing protein levels in malting barley
For optimum economic returns, fertilizer applications should be managed to apply sufficient N to attain the highest possible yield, without increasing protein content beyond the acceptable levels. For optimum profitability, a fertilizer management system must consider the balance among the major nutrients rather than simply N and moisture in isolation.
IPNI-1990-CAN-MB4
24 May 2001
Justification
- Among the major factors cited for rejection of producer malting barley samples is excess protein. The average percentage protein of the Canadian barley crop varies from year to year as the environmental factors vary, but generally falls in the range of 12.0 to 12.7%. However, the protein content preferred by the malting and brewing industries is between 10.5 and 12.5%. Excess protein leads to costly production problems for both the maltsters and brewers.
The protein content of barley is determined by both genetic and environmental factors. The major environmental factors influencing the expression of the genetic potential protein content of the specific variety are moisture and soil fertility. There tends to be an inverse relationship between yield and protein content, at a given level of N fertility. As yield increases, protein content decreases, if N is kept constant. This is due to the dilution effect. Increasing yield tends to increase the volume of material through which the protein must be distributed. Therefore, when moisture levels are high and the yield potential is high, protein tends to be low. Additions of fertilizer N tend to increase protein content of barley. However, the initial increments of N applied to a crop will generally be used to increase yield until the yield potential is constrained by some other factor, generally moisture or another nutrient. After that, protein content will begin to increase significantly.
For optimum economic returns, fertilizer applications should be managed to apply sufficient N to attain the highest possible yield, without increasing protein content beyond the acceptable levels. Current recommendations for major crops in Manitoba are based on the long term average moisture levels, from arid to irrigated, for the specific area where the crop is to be grown. In malting barley, effects of moisture and the availability of other nutrients can have a major impact on the potential yield of the crop and on the amount of N required to attain the optimal yield/protein balance.
Although N and moisture levels are the factors which generally have the greatest impact on grain protein level, availability of P, K and S also influence both grain yield and protein. Sever deficiency of P, K or S can interfere with protein synthesis. Less severe deficiencies may inhibit yield to a greater extent than protein production and lead to increased percentage protein, although total protein production per hectare is reduced. Potassium may also have important effects on translocation of nitrogen within the plant, which will influence both yield and protein level. In addition, KCl fertilizer has been shown to influence disease incidence, which impacts on total yield and grain quality. Therefore, for optimum profitability, a fertilizer management system must consider the balance among the major nutrients rather than simply N and moisture in isolation.