Effect of an acidifying nitrogen fertiliser and lime on soil pH and wheat yields. 2. Plant response

This paper reports the effects of an acidifying fertiliser on wheat yields and mineral composition in the first 10 years of trials at Merredin, Wongan Hills, and Newdegate, described in the previous paper. There were grain yield increases from application (kg/ha.year) of 17.5 N + 7.6 P and 35 N + 15.2 P in all years except 1980 (Wongan Hills and Newdegate) and 1989 (Merredin). At Merredin, 3 t/ha of limestone increased grain yields in all years except 1982 and 1983. At Wongan Hills, limestone increased yields in the continuous cropping system, in the presence of high N + P, during 1986 and 1989. At Newdegate, grain yield responses to lime were recorded in 1980, 1981, 1982, 1986, 1988, and 1989; limestone resulted in decreased wheat yields in 1984 because of an increase in the severity of the root disease take-all (caused by Gaeumannomyces graminis var. tritici), and decreased lupin yields in 1987 because of manganese deficiency. There were a few responses at Merredin and Newdegate to low rates of limestone with each N + P application. Application of the magnesium (Mg) + potassium (K) + molybdenum (Mo) in addition to limestone gave isolated responses at all sites. Concentrations of calcium (Ca), Mg, and K at the 1989 plant sampling were highest at Wongan Hills and lowest at Merredin. Calcium concentrations were higher at Merredin and Newdegate following N + P application, but lower at Wongan Hills. Application of N + P reduced the concentration of Mg at Merredin and Wongan Hills, but increased Mg at Newdegate. The concentration of K was decreased at all sites by N + P. Limestone had no consistent effect on Ca concentrations but increased the concentrations of Mg and K at Merredin and K at Newdegate. Where Mg + K + Mo had been applied in 1980, concentrations of Ca decreased and K increased, while there was no consistent effect on Mg concentration. The Mo concentration in plant shoots was reduced at all sites by increasing rate of N + P and increased by application of lime and Mo in 1980. Grain Mo concentrations were very low at Merredin and Wongan Hills, even in the absence of N + P. Concentrations at Newdegate were reduced by increasing N + P rate. Application of limestone increased grain Mo concentrations at all sites, but these were still lowered by N + P application. Concentrations were also increased by the application of Mo in 1980, but fell with time, particularly with application of N + P.