Ground Cover Supplement : GC Supplement - Tactical cereal agronomy
18 Frost Grazing and stubble under frost research spotlight Stubble and grazing systems are being investigated for their capacity to lower frost risk in cropping systems By Dr Ben Biddulph and Sarah Jackson MODIFIED FARMING SYSTEMS are being examined as one part of a multidisciplinary approach to frost mitigation by an Australia-wide team of researchers in the GRDC's National Frost Initiative (NFI). The research is seeking to understand how crop canopies and management practices can be manipulated to change the dynamics of the soil heat bank -- the process by which the soil stores heat during the day and releases it overnight. Farming practices that maximise soil heat storage include soil amelioration methods such as clay spreading or delving, along with rolling, partial removal of stubble load and crop canopy manipulation. Release of heat overnight into a crop canopy reduces the severity and duration of frost. Research to date has shown that frost damage in cereal crops is a function of frost severity (the minimum temperature experienced), frost duration (typically measured as hours below 0°C) and frost timing in relation to crop developmental stage. In wheat, temperatures below 2°C can cause cold-induced sterility, which is not readily visible without dissection, while temperatures below 0°C can lead to head frost and temperatures below --2°C can lead to head and stem frost with clearly visible signs of freezing damage on whole heads and stems. The NFI has evaluated the capacity of four management practices to manipulate the soil heat bank: stubble management, crop grazing, canopy management and soil amelioration. Trials have been carried out in medium and low-rainfall environments in the western, southern and northern GRDC regions to determine the effects of these practices on the severity and duration of frosts. An enduring achievement of the project has been the development of standard frost measurement techniques and protocols for use in large, precision-agriculture-scale trials. STUBBLE The stubble management trials have determined the effect of stubble load and architecture (standing or horizontal) on frost severity and duration. Results from the first year of trials indicate that higher stubble loads, either standing or horizontal, can increase the severity and duration of frost events. Stubble loads above 1.5 tonnes per hectare in low-production environments (2 to 3t/ha grain yield) and 3t/ha in high- production environments (3 to 5t/ha) generally increased the severity and duration of frost events and had a detrimental effect on yield under frost. Stubble is a very effective insulator, stopping heat from penetrating the soil during the day and from re-radiating into the canopy overnight (Figure 1). As a result, canopy temperatures with stubble are often 0.5°C colder and also colder for longer (one to two hours per night below 0°C) than those without stubble, making the crop more at risk of freezing and frost damage (Figures 2a and 2b). GRAZING Grazing trials at Kellerberrin and Newdegate, Western Australia, showed that two weeks of moderate and heavy grazing will delay the flowering time of wheat and barley by up to a week, potentially reducing the risk of the cropping program. Canopy temperatures above stubble are often 0.5°C colder and also colder for longer (one to two hours per night below 0°C) than those without stubble. FAST FACTS SOURCE: JENKINSON AND BIDDULPH, 2014 Stubble loads at seeding: (3.5t/ha; blue, 2.5t/ha; red and 0.5t/ha; green). Bars followed by a different letter are significantly different. FIGURE 1 Temperature dynamics in a crop canopy during frost events adapted from Rebbeck & Knell (2007). FIGURES 2a and 2b Frost severity and duration during spring at Nyabing in 2013 in relation to stubble loads at seeding. Minimum canopy air temperature (ºC) a a a a a aa a a a a a a a a a a a a a a a aa a a b b b b b b b b b bb bb bb b b b b bb bb b c c c c c c c 0 --1 --2 --3 --4 --5 --6 5/9 6/9 9/9 27/9 1/10 10/10 12/10 13/10 14/10 15/10 17/10 18/10 21/10 22/10 AVG DAYTIME NIGHT-TIME Outgoing radiation Outgoing radiation MAXIMISE STORAGE OF HEAT Soil Soil surface Allow heat to be released from soil at night and reach crop heads Maximise interception of incoming radiation Hours below temperature threshold Minimum canopy air temperature threshold (ºC) Date 70 60 50 40 30 20 100 --4 --3 --2 --1 0 SOURCE: REBBECK AND KNELL, 2007 Stubble reduces the storage of heat in the soil during the day and reduces the loss of heat from the soil at night.
GC Supplement - Grain storage 2015
GC Supplement - Spray application 2016