Summer cover crops | central and southern NSW

At the Wagga Wagga Grains Research Update, Colin McMaster shared the latest research on summer cover crops, specific to central and southern New South Wales in winter dominated rainfall areas. We looked at what are the key drivers for retaining summer fallow moisture, and it does that always lead to increases in grain yield. He started with some key advice for local growers - before you make any cover crop decisions, understand the pros and cons. So some of the benefits are you’ve got to have reduced wind erosion, you’re going to have cooler temperatures. You’re going to have a more consistent soil temperature.

00:59 - You’ve also got less herbicide applications over the summer fallow period. There’s actually going to be forage value from those grazing crops. You’re potentially going to be increasing your total carbon percentage and therefore you’re going to be improving your microbial activity as well within that. The cons of summer cover crops are you’ve got reduced mineral nitrogen availability, you’ve got reduced grain yield, you’ve got higher risk of soil water deficit in low rainfall years, so you’re increasing your risk profile. You could have patchy crop establishment and you’re also increasing potentially your disease risk for the following winter cash crop.

01:40 - Since November 2018, Colin’s managed a range of research trials at Parks and Canowindra to better understand how summer cover crops can benefit and integrate with the broader farming system. The primary aim of this particular trial is to determine what’s the net water cost to grow a cover crop. What’s the net water gain for the following winter cash crop? And then what’s going to be the impact on the following grain yield from that winter cash crop. So so that’s the primary purpose. The secondary purpose is to observe how does it fit within the farming system. So how is it going to impact nitrogen levels, total carbon levels? What’s the grazing value of those cover crops? What’s going to be the disease implications of those cover crops? So there’s a lot of other secondary questions that we’re also trying to address.

02:28 - It’s all part of a wider GRDC investment on summer cover crops in the northern region with similar trials set up across New South Wales and Queensland growing areas. As Colin explains, his central New South Wales trials have delivered some surprising insight on cover crop performance. It was quite surprising from these trial results that the soil water recharge following a cover crop was was really quite high. So if you get a really wet year or you get rainfall post cover crop termination, the recharge is going to be really quick, which is fantastic. But if you don’t get any rainfall after you terminate the cover crop, you’re obviously going to be in a soil water deficit.

03:08 - So there’s a benefit, but there’s also a risk associated with that. Even if you do get a really wet year, the soil water can catch up, but you’re going to leave a nitrogen deficit behind that’s probably going to need correcting for your following winter cash crop. So you really need to be aware of, you know, really aware of those those factors. For grain only operations, the trials highlight the risks associated with growing cover crops in a short fallow. Both of the trial sites showed that grain yield reduction was reduced by growing a cover crop.

03:41 - So really, you’re better off to try and just conserve stubble by using current techniques, retaining stubble. There’s all sorts of things disc machines, stripper front, there’s a lot of technology out there to try and retain your stubbles and control your subtle weeds are probably the best best management still. The main reason for that is you’re not having to grow any biomass that using water to grow that biomass, you’re just growing the grain. But if your goal posts is that you’ve got a bare, bare ground and you need ground cover from an erosion perspective, it makes a lot of sense. Though from a mixed farming perspective, it’s a different story as there are more options to utilise that cover crop biomass.

04:23 - So if you’ve got livestock within the system, livestock are worth a lot of money and you can convert that biomass to dollars. You just need to keep in mind that if you are going to be grazing it and trying to grow a cash crop the following season, you really need to make sure it’s a high output system. So your nutrition needs to also be well-suited to that and not have your nutrients limited. Coming to the end of his presentation, Colin offered some good cover crop advice for all growers to consider. The key thing to take out of this research is be very clear of what your goals are if you’re interested in cover cropping, there’s many pros and cons.

05:03 - Be aware of all the pros, be aware of all the cons, understand the mechanics of it so you can see whether it’s actually going to achieve your your particular goal posts. So just be aware of the risks and the rewards. Colin McMaster from the New South Wales Department of Primary Industries. And this video is one in a series of update videos recorded at the 2020 GRDC Grains Research Updates. .