Soil factors influencing growth and yield of narrow-leafed lupin and field pea in Western Australia

Abstract

Crop growth and grain yield of narrow-leafed lupin and field pea were compared in 40 field trials in the Western Australian wheatbelt in 1988, 1989, and 1990. Trials were arranged in clusters of 2 or 3 in close proximity, but on contrasting soil types. This enabled seasonal effects on growth and yield to be separated from soil type effects. Soil pH ranged from 4.1 to 5.8 at the surface and from 3.7 to 8.4 at 50 cm, A-horizon depth from 9 cm to >70 cm, and clay content at 50 cm from 0 to 54%. Other soil properties also varied across wide ranges. Some soil properties were closely correlated with one another; pH, electrical conductivity (EC), gravimetric water content (θ_g) at field capacity and at wilting point, and depth of the A-horizon were all correlated.

Narrow-leafed lupin grain yield was 2.6 times as variable between trials within locations as field pea yield, which, on average, was 32% greater than narrow-leafed lupin yield. The pH, EC, θ_g) at field capacity, and θ_g) at wilting point each explained a large proportion of lupin yield variability on their own, but because they were closely correlated with one another, it was not possible to determine which had the primary effect on grain yield. I believe, on the basis of other work, that pH is an important factor in its own right. A-horizon depth explained 9% of the lupin trial variance but this was largely due to its correlation with pH and other related soil properties. When the effects of these were removed, depth still reduced the between-trial variance within locations but did not affect species differentially. Bulk density also reduced between-trial variance within locations without affecting species differentially. Altogether soil properties explained 42% of the lupin site variance but none of the pea site variance.

The pH and correlated soil properties also explained much of the species site variance in dry matter production at maturity, but not in harvest index. Bulk density and A-horizon depth had small, but significant, effects on harvest index. Therefore, soil type affects grain yield in these species largely through its effect on dry matter production.

I conclude that field pea is equally well adapted to the full range of soils in this study. Narrow-leafed lupin does not yield as well on soils with subsoil pH greater than 6.5 as on more acid soils. The depth of the A-horizon is only useful as a criterion for judging the suitability of a soil for growing narrow-leafed lupin insofar as it is correlated with pH.