Very Low Fertility

Low grain yield and low grain protein indicate very low fertility levels. This is confirmed if the test weight of the grain is acceptable (≥ 60 lbs/bushel).This situation normally occurs when the crop is seriously under-fertilized for nitrogen and sulfur, or these nutrients were lost by leaching, denitrification or volatilization. Reevaluate your fertility program in the future and pay attention to soil nutrient levels and fertilizer rates when developing a fertility program.
Washington State University