Effect of successive cropping with nitrogenous fertilizers on wheat yields

Abstract

Wheat was grown for twelve successive years at three sites with five rates of nitrogen either as calcium ammonium nitrate, ammonium sulphate or urea applied each year to the same plots. There was a long term yield decline, with and without nitrogen, on the site at Wongan Hills, but not at Merredin or Beverley. At each of the three sites there was no indication of a need for higher rates of nitrogen fertilizers with time to maintain yields. At Wongan Hills and Merredin, yields were depressed in most years when the highest rate of ammonium sulphate was used each year. Grain protein contents were low and did not decrease with time.