Sustaining productivity of a Vertosol at Warra, Queensland, with fertilisers, no-tillage or legumes. 9. Production and nitrogen benefits from mixed grass and legume pastures in rotation with wheat

Abstract

Abstract. Reduced supplies of nitrogen (N) in many soils of southern Queensland that were cropped exhaustively with cereals over many decades have been the focus of much research to avoid declines in profitability and sustainability of farming systems. A 45-month period of mixed grass (purple pigeon grass, Setaria incrassata Stapf; Rhodes grass, Chloris gayana Kunth.) and legume (lucerne, Medicago sativa L.; annual medics, M. scutellata L. Mill. and M. truncatula Gaertn.) pasture was one of several options that were compared at a fertility-depleted Vertosol at Warra, southern Queensland, to improve grain yields or increase grain protein concentration of subsequent wheat crops. Objectives of the study were to measure the productivity of a mixed grass and legume pasture grown over 45 months (cut and removed over 36 months) and its effects on yield and protein concentrations of the following wheat crops.Pasture production (DM t/ha) and aboveground plant N yield (kg/ha) for grass, legume (including a small amount of weeds) and total components of pasture responded linearly to total rainfall over the duration of each of 3 pastures sown in 1986, 1987 and 1988. Averaged over the 3 pastures, each 100 mm of rainfall resulted in 0.52 t/ha of grass, 0.44 t/ha of legume and 0.97 t/ha of total pasture DM, there being little variation between the 3 pastures. Aboveground plant N yield of the 3 pastures ranged from 17.2 to 20.5 kg/ha per 100 mm rainfall. Aboveground legume N in response to total rainfall was similar (10.6-13.2 kg/ha.100 mm rainfall) across the 3 pastures in spite of very different populations of legumes and grasses at establishment. Aboveground grass N yield was 5.2-7.0 kg/ha per 100 mm rainfall.In most wheat crops following pasture, wheat yields were similar to that of unfertilised wheat except in 1990 and 1994, when grain yields were significantly higher but similar to that for continuous wheat fertilised with 75 kg N/ha. In contrast, grain protein concentrations of most wheat crops following pasture responded positively, being substantially higher than unfertilised wheat but similar to that of wheat fertilised with 75 kg N/ha. Grain protein averaged over all years of assay was increased by 25-40% compared with that of unfertilised wheat.Stored water supplies after pasture were <134 mm (<55% of plant available water capacity); for most assay crops water storages were 67-110 mm, an equivalent wet soil depth of only 0.3-0.45 m. Thus, the crop assays of pasture benefits were limited by low water supply to wheat crops. Moreover, the severity of common root rot in wheat crop was not reduced by pasture-wheat rotation.

Action learning in partnership with Landcare and catchment management groups to support increased pasture sowings in southern inland Queensland

“…This increase in pasture area will increase the groundcover and natural resource outcomes sought by QMDC in the region, while enhancing soil nitrogen and carbon levels and crop production (e.g. Dalal et al 2004aDalal et al , 2004bStrong et al 2006).…”

Poor adoption of ley-pastures in south-west Queensland: biophysical, economic and social constraints

“…Dalal et al (1998) also reported that this ley-pasture was an effective way to increase soil organic matter, producing an extra 80 kg N/ha per year, boosting subsequent wheat yields and protein to prime hard, and was found to be a more profitable system than continuous wheat cropping without fertiliser N. From the same study, it was also noted that grass production for grazed pastures was nearly twice that of a pasture that was cut and removed (Strong et al 2006). This indicated an additional advantage of grazing; namely, nutrient recycling from dung and urine in grazed pasture, promoting increased growth, particularly of N-starved grasses (Strong et al 2006). However, the limitations of grass + legume system included an unreliable pasture establishment, requiring adequate stored water before sowing, and a greater depletion of soil water, which can reduce the yield of the subsequent cereal crop if water deficit is not replenished through practising a long fallow of at least 14-18 months (Dalal et al 1998).…”

“…The mix of grass + legume pastures can provide continuity of quality feed throughout the year for at least 4 years (Dalal et al 1998). Dalal et al (1998) also reported that this ley-pasture was an effective way to increase soil organic matter, producing an extra 80 kg N/ha per year, boosting subsequent wheat yields and protein to prime hard, and was found to be a more profitable system than continuous wheat cropping without fertiliser N. From the same study, it was also noted that grass production for grazed pastures was nearly twice that of a pasture that was cut and removed (Strong et al 2006). This indicated an additional advantage of grazing; namely, nutrient recycling from dung and urine in grazed pasture, promoting increased growth, particularly of N-starved grasses (Strong et al 2006).…”

“…Lucerne. This is the most common legume on cropping soils and widely used in southern Queensland and northern New South Wales although it fails to persist in sufficient plant densities for more than 2 years in Queensland (Pengelly and Conway 2000;Strong et al 2006). Lucerne as a ley-pasture generally provides high-quality forage for grazing for 1-3 years.…”

“…The limitations of this system include greater depletion of soil water, reducing the wheat yield until water deficit is replenished. Lucerne forage can also cause bloating in cattle, and sowing of lucerne under wheat, a common practice for lucerne establishment, can be unreliable in dry seasons (Holford and Doyle 1978;Dalal et al 1991;Angus et al 1996;Holford and Crocker 1997;Weston et al 1997;Strong et al 2006).…”