Legume residue management in sugarcane

Legume residue management in sugarcane


I’m Derek Sparkes, I work for the Department
of Agriculture Fisheries and Forestry in Queensland and I’m going to talk about Legume Residue
Management today. There are a number of different legumes grown as break crops in the sugarcane
industry. There’s lablab, cowpeas and, more recently, soybeans, they’re grown for the
summer period and then the cane is planted in the following winter. It’s very important that we manage these legume
residues correctly because they can contain up to 200 or 300 kilograms of nitrogen per
hectare and we want to ensure that that nitrogen becomes available to the cane and not lost
to the environment. We have two main strategies to try to avoid
losing nitrogen to the waterways, one of those is to keep the legume residue, regardless
of what type of legume it is, keep the residue away from the soil. As long as it is above
the ground and in the air it will not break down and mineralise to nitrogen as quickly
as it would do being incorporated into the soil. So spraying out the residue or spraying
out the crop is a good thing, keeps it above the ground but also kills out any other weeds
and things that you don’t want seeding in the legume crop. So that’s one strategy we use. Mulching is
another one and mulching is not a bad idea, it breaks up the material but it still leaves
it lying on the surface of the ground so it’s less effective than spraying out but it still
does not get incorporated into the soil so the bacteria in the soil can’t really get
stuck into it. To try and match the requirement of the crop
with the availability of the nitrate a zero-till method is preferable but trials have been
done and it is very difficult to get zero-till to work with cane because a lot of cane billets
have to go down a very small gap and it is difficult to get contact with the billets
and it’s difficult to get depth of planting so there are quite a few issues with that
but in a perfect world, in relation to nitrogen management, zero-tilling into standing legume
stubble would be perfect. That’s not always the case and so we have to do tillage and
we try and do it as close as we can to planting. So in conclusion, you need to delay the breakdown
of the legume to nitrate and the way to do that is to keep it out of the soil and delay
the incorporation until the very last minute and by doing that you will get your best bang
for your buck.

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