Productivity and rotational benefits of grass, medic pastures and faba beans in a rainfall limited environment

This study was undertaken to ascertain whether pulses, instead of pasture legumes, were more beneficial to grain yields by the following cereals in ley rotation systems. We evaluated growth processes for pastures or pulses and growth and yields for the following sequential crops of wheat and barley in a 3-crop rotation. The pasture or pulse phase that formed the main treatments consisted of grass pastures (Grass), medics (Medic) or faba beans that was either green manured (Faba-gm) or harvested for grain (Faba-gr). The rotations were initiated in two phases with Phase 1 starting in 1994 and Phase 2 in 1995, and each phase ran over 2 rotation cycles lasting 6 years. Despite differences in dry matter (DM) produced in the shoots and roots by the pastures and faba beans in the first years, they had similar seasonal evapotranspiration (ET) so water stored in the 100 cm profile of the soil was always similar when wheat was planted. By contrast, inorganic N in soil at wheat planting was always higher in legume rotations than in Grass and these differences persisted to the barley crop. Cereals in rotations with faba beans (Faba-gr and Faba-gm) produced more DM and grains than in Grass. In only 2 out of 8 croppings of cereals did wheat or barley in Medic out-yield those in Grass. These yield differences were not associated with uptake of soil N or use of soil-water by the cereals, but possibly due to lower levels of Pratylenchus neglectus in the soil under rotations with faba beans compared with pasture. Increased N supply after legumes or from fertilizer, however, increased grain protein in the cereals. This study showed that rotations with faba beans produced higher yields for the following cereals than with grassy or legume pastures, also green manuring of faba beans produced no advantage in yield for the cereals.