Ground Cover Supplement : GC Supplement - Profitable pulses and pastures
15 Break crop and pasture options A two-year break reduced weed seedbanks for consistent improvement in cereal yield. GRDC Research Code DAN00157 More information: Dr Eric Armstrong, Wagga Wagga Agricultural Institute, email@example.com FIGURE 1 Dry matter production pattern of MorganA field peas at Wagga Wagga, NSW, under good growing conditions and free of disease and weeds. Dry matter Note: The amount of dry matter produced depends on the season and typically varies between 2 to 10t/ha. Notice how vegetative DM falls towards the end of the season as plant nutrients are remobilised from vegetative parts into filling grain. Desiccate is the chemical termination of plant growth using sprays such as diquat or glyphosate. In the above graph, the red arrow points to the timing and stage of field pea growth (flat pod here) that the desiccant (chemical spray) is best applied in order to prevent any seed-set in the targeted weeds. Sowing date: 29 May Flowering: 2 Oct End flowering: 24 Oct Maturity: 25 Nov Max crop growth rate 80-100kg DM/ha/day Flat pods Desiccate resistant weeds Flowering period Grain Max DM, Max N2 fixed 29 May 23 Jun 18 Jul 12 Aug 6 Sep 1 Oct 26 Oct 20 Nov Stems, leaves etc. SOURCE: NSW DPI break crops were grown over five years at four different locations involving several Mallee soil types. The trials included Karoonda in the southern South Australian Mallee (2009 and 2010), Mildura in the northern Victorian Mallee (2011 and 2012), Chinkapook in the northern Victorian Mallee (2011 and 2012) and Hopetoun in the southern Victorian Mallee (2009, 2010 and 2011). The break crops grown at each site varied but included species of legume (vetch, field peas, lupins, volunteer pasture), brassica (canola, juncea) and grass (cereal rye, barley, oaten hay). The effects of the break crop on the levels of nutrition, diseases and weeds were measured in the trials at varying levels of intensity, depending on the key limiting factors at each site. The project found that in low- rainfall environments, the effect of breaks on subsequent wheat yields is usually more consistent across soils, seasons and break type than the yield of break crops. Combined analysis of trials hosted by BCG and MSF show that first-year effects of legumes are generally more reliable than oilseeds for improving subsequent wheat yield. Increased nitrogen supply could be measured for up to two years following the break and played a key role in break effects at Karoonda and Hopetoun where weed burden was low. However, disease breaks tended to only last for one wheat-growing season. Paddocks with a high grass-weed burden required a two-year break to reduce the weed seedbank to a level that allowed consistent improvements in cereal production. Over a three to four-year period, including legume and canola breaks in the sequence was at least as profitable as continuous wheat. The benefits of the break crop to subsequent wheat yields are critical to determining the overall value of the break. For example, some trials produced significant profit gains from two years of break crops compared to continuous wheat, while other trials had variable gross margins. So, where to from here? These results raise the question for low-rainfall-region growers: 'Can I have a break year that costs me less than what a tonne of wheat is worth?' The project lays the foundation for the evaluation of new lower-risk break options for low-rainfall environments. □ GRDC Research Codes CSA00025, BWD00012, CSP00111, DAS00119 More information: Dr Therese McBeath, CSIRO, firstname.lastname@example.org Pulse management guide When weeds are not the priority Management: natural maturation and grain harvest Goal: to maximise grain yield and profit while at the same time providing rotational benefits. Method: This is the most traditional and widespread practice for cultivating pulses in NSW and is based on well-developed agronomy and crop management strategies from sowing through to harvest. This option assumes weeds are fully managed by conventional rotation and herbicides. Management: brown manuring Goal: to maximise N2 fixation, N-benefit and to conserve soil moisture. Method: The amount of N2 fixed is linked closely to dry matter (DM) production of the legume (Figure 1), therefore 'manure' the weed-free pulse close to its maximum DM. For a typical Morgan PSE 23A (long-season) field pea crop sown at Wagga Wagga, NSW, in late May, this would mean desiccating around the end of October (Figure 1). When weeds are the priority, particularly if herbicide resistance exists Management: brown manuring Goal: total control of weeds including herbicide resistance, and to fix some N and conserve soil moisture. Method: It is imperative to desiccate the crop at or before the milky dough stage of the targeted weed. This often coincides with the flat pod stage of the pulse and inevitably falls well short of the crop's peak DM. At this stage the crop is growing at its maximum rate (about 80 to 100kg DM/ha/day), so the amount of N fixed will be proportionally reduced according to its growth stage at desiccation (Figure 1). This cost is non-negotiable and essential to ensure complete weed control. Management: crop topping/desiccation followed by grain harvest Goal: to maximise grain yield and profit while at the same time providing rotational benefits. Method: This is the 'have your cake and eat it' scenario. It is a good option for cleaning up scattered weeds and to eliminate weed seed-set in all weedy situations including herbicide resistance. It uses the conventional approach of grain harvest, plus crop-topping/desiccation at the critical growth stage of the weed. Timing is critical -- it depends on the pulse variety reaching physiological maturity at or before the time of crop-topping/desiccation. Most pulse varieties (chickpeas, lupins and kaspa field peas) are unsuitable as they are too late and lose too much grain yield. However, newer varieties of field peas are quicker-growing and better suited to crop-topping. As field peas are sown later they also extend the pre-sowing weed- control window. Suitable early-flowering and early-maturing field pea varieties currently include PBA PearlA, SW Celine and PBA OuraA.
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