GCTV17: Legume Nodulation - Scoring Samples
Maarten Ryder: University of Adelaide Now we've got three piles of plants on the
back of the ute, one from each of the buckets and what we're going to do now is sort each
pile into plants that are adequately nodulated and those that are not adequately nodulated.
Now for peas on a heavier soil we're looking for 50 to 100 nodules per plant on a lighter
soil we might be happy with 20 per plant.
You can do this with the plant I the palm of your hand, can spread out the roots a little
bit and start counting and it is probably important when you first do this to have a
go at counting nodules you'll pretty soon find out what 10 nodules looks like and you'll
be able to count in groups of 10 and its actually even easier if you've got a white tray of
any kind with a bit of water in it you can put the plant in there and just remove any
remaining soil and you can easily see the nodules you may even see the pinkness of the
nodules, pink nodules are what we want to see because they're actively fixing nitrogen.
What we don't want to see is white or green nodules, which are inactive.
On this root system they mostly look pink which is what we're looking for however I
think there's probably only about 30 nodules so I don't think that's adequate I'll put
that over on the left here and I'll grab another plant.
One of the other advantages of sampling plants in your paddocks and having a look at the
root systems is that you can check the health of those root systems as well.
You can see if there is some herbicide damage or some root disease going on.
This plant has got about 50 nodules on it so we'll consider it adequately nodulated.
Now on this plant we can see the nodules are distributed all over the root system, this
is because this crop was not inoculated and if we were dealing with an inoculated crop,
a seed inoculated crop particularly we would expect a lot of nodules around the crown,
where the seed was here, we'd expect a lot of nodules here and on the early roots where
we have early nitrogen fixation gives the plant a good start.
Where the nodules are further away we're getting later nitrogen fixation, which is also important.
Well I've got the numbers now and we'll look at what they mean.
From the first pile the first sampling site we got 90% adequate, for the second we got
55, for the third we got 60, for an overall average of 70.
I might add across the field we always get variation so its good to do it at three separate
spots but what I could tell the grower here is that the nodulation is adequate, there's
no need to change anything in his system.
So what happens if the nodulation is poor?
If you inoculated and you're not seeing enough nodules you should make sure you're using
the right inoculant group and that it's been and used correctly but you can also run into
trouble with root disease or herbicide damage reducing the root system itself and therefore
also reducing the nodulation.
Overall going from the paddock, taking the samples and bringing them back, washing them
and having a look at the roots I think it should take roughly an hour for that whole
process for a paddock to assess how successful nodulation has been.
What we're really looking for is farmers to monitor what's going on with their crops,
their legume crops and inoculation and nodulation because really we want to optimize or maximise
the nitrogen fixation which gives benefit to this crop as well as to following crops.
If you are not sure about what you're seeing when you go out and do this kind of work pleas
go online to the University of Adelaide website or GRDC website or you can contact the researchers.
ends