Sustaining productivity of a Vertosol at Warra, Queensland, with fertilisers, no-tillage or legumes. 7. Yield, nitrogen and disease-break benefits from lucerne in a two-year lucerne - wheat rotation

Abstract

Abstract. Continuous cultivation and cereal cropping of southern Queensland soils previously supporting native vegetation have resulted in reduced soil nitrogen supply, and consequently decreased cereal grain yields and low grain protein. To enhance yields and protein concentrations of wheat, management practices involving N fertiliser application, with no-tillage and stubble retention, grain legumes, and legume leys were evaluated from 1987 to 1998 on a fertility-depleted Vertosol at Warra, southern Queensland. The objective of this study was to examine the effect of lucerne in a 2-year lucerne-wheat rotation for its nitrogen and disease-break benefits to subsequent grain yield and protein content of wheat as compared with continuous wheat cropping.Dry matter production and nitrogen yields of lucerne were closely correlated with the total rainfall for October-September as well as March-September rainfall. Each 100 mm of total rainfall resulted in 0.97 t/ha of dry matter and 26 kg/ha of nitrogen yield. For the March-September rainfall, the corresponding values were 1.26 t/ha of dry matter and 36 kg/ha of nitrogen yield. The latter values were 10% lower than those produced by annual medics during a similar period. Compared with wheat-wheat cropping, significant increases in total soil nitrogen were observed only in 1990, 1992 and 1994 but increases in soil mineralisable nitrogen were observed in most years following lucerne. Similarly, pre-plant nitrate nitrogen in the soil profile following lucerne was higher by 74 kg/ha (9-167 kg N/ha) than that of wheat-wheat without N fertiliser in all years except 1996. Consequently, higher wheat grain protein (7 out of 9 seasons) and grain yield (4 out of 9 seasons) were produced compared with continuous wheat. There was significant depression in grain yield in 2 (1993 and 1995) out of 9 seasons attributed to soil moisture depletion and/or low growing season rainfall. Consequently, the overall responses in yield were lower than those of 50 kg/ha of fertiliser nitrogen applied to wheat-wheat crops, 2-year medic-wheat or chickpea-wheat rotation, although grain protein concentrations were higher following lucerne.The incidence and severity of the soilborne disease, common root rot of wheat caused by Bipolaris sorokiniana, was generally higher in lucerne-wheat than in continuous wheat with no nitrogen fertiliser applications, since its severity was significantly correlated with plant available water at sowing. No significant incidence of crown rot or root lesion nematode was observed. Thus, productivity, which was mainly due to nitrogen accretion in this experiment, can be maintained where short duration lucerne leys are grown in rotations with wheat.

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

“…Nitrogen fixed by lucerne for example appears closely associated with the total amount of dry matter produced; on average, 20-25 kg N is fixed for each tonne of legume dry matter produced (Peoples and Baldock 2001). At this site, dry matter production and N yields of lucerne were closely correlated with the total (October-September) growing season rainfall as well as March-September rainfall (Dalal et al 2004a). Each 100 mm of total growing season rainfall resulted in 0.97 t/ha of dry matter and 26 kg/ha of aboveground N. Response of lucerne to rainfall in autumn and winter (March-September) was 1.26 t/ha for dry matter and 36 kg/ha for aboveground N. These values were 10% less than that for autumn and winter-growing annual medics for the same period.…”

“…The soil is a Vertosol (Typic Chromustert) that has lost 70% of organic C (from 2.23 to 0.68%) and total N (from 0.203 to 0.06%) from the 0-0.1 m layer after 50 years Mayer 1986b, 1986c). Detailed description of the soil, and mean monthly maximum and minimum temperatures, and mean monthly rainfall, and growing season rainfall at the field site (1987-98) are described in earlier papers of this series (Dalal et al 2004a;Weston et al 2002). Briefly, the soil contains 56, 17 and 27% clay, silt and sand, respectively.…”

“…To continue to crop these lands profitably and sustainably requires N supply to be supplemented by either the application of N fertiliser (Holford and Doyle 1992;Strong et al 1996b) or inclusion of legumes in rotation with cropping (Armstrong et al 1999a(Armstrong et al , 1999bDalal et al 2004aDalal et al , 2004bHolford 1980;Holford and Crocker 1997;Holford et al 1998;Hossain et al 1996b;Littler 1984;Weston et al 2002;Whitehouse and Littler 1984).…”

“…In the cereal growing areas of northern New South Wales and southern Queensland, it has been shown that periods of legume pasture even as short as 2 years of annual medics or lucerne, significantly increases soil mineral N available for subsequent cropping as well as yields and protein concentrations of subsequent cereal grain (Dalal et al 1991(Dalal et al , 2004a(Dalal et al , 2004bHolford et al 1998;Hossain et al 1996aHossain et al , 1996bWeston et al 2002). Higher than expected pasture production with a mixture of grasses and legumes and the summer-dominant rainfall that favours grasses prompted the question as to whether mixed pastures might impart similar benefits as pure legume swards while improving the quantity or quality of forage for animals while reducing the risk of bloating.…”

Modelling of lucerne (Medicago sativa L.) for livestock production in diverse environments

“…It is commonly grazed, or cut and conserved as hay or silage. It is 60 also often integrated into crop-livestock systems as a ley phase in cropping rotations to control weeds 61 and disease (Dalal et al 2004), to augment soil nitrogen and carbon stocks (Angus and Peoples 2012), 62 and to improve soil structure (Hanley et al 1964) and water infiltration (McCallum et al 2004). Lucerne 63 is also grown in order to capitalise on summer rainfall to produce quality forage; it also alleviates 64 growth activity (the inverse of which is known as fall dormancy) from winter inactive to highly winter 70 active (Humphries et al 2004).…”