23 July 2024. Paul McIntosh, Pulse Australia and WeedSmart
The above photo shows a well-developed chickpea root system with the old seed body still coated in blue Thiram fungicide in a fairly good soil type on the Darling Downs.
The question we should all ask is where are all the root nodules containing the Rhizobia bacteria? Root nodules are irregular pea shaped creamy lumps on the root system of many legume plants like Chickpeas.
Inside these nodules are billions of microscopic rhizobia bacteria, very genetically diverse with nearly 100 named species already and more new ones each year. These sensitive little guys need carbon and other macro and micronutrients, water at a suitable pH of 6.0 to 7.5, oxygen to breathe and preferably temperatures from 15 to 30 degrees C (above 35 degrees is deadly) to exist and procreate. Include in the dangerous and deadly list to these highly beneficial microbes, is many of the toxic chemicals we use, including the heavy metals in Fertilizers. By the way, the bacteria are not coated with 50 + sunscreen, so shade is important as well as the cool atmosphere. So, why are they important to our legume plants?
The simplistic explanation is that active root nodules full of these microbes, develop a symbiotic association with the roots of the legume plant for their carbohydrate needs and as a side event fix nitrogen from the atmosphere for the legume plants benefit.
Now surprise, our legume plants do require nitrogen to grow and produce, so let us examine our humble chickpea plant’s needs.
We have a large commercial crop of Desi chickpeas this winter in Queensland and Northern NSW, yet many are unaware of how much nitrogen it takes to produce a modest yield of let’s say...around 2.0 tonne per hectare. The requirements are approximately 160 kgs of Nitrogen per hectare available to the chickpea root system.
For a 3.0 tonne per ha yield of chickpeas, it is around 240 kgs per hectare of plant available Nitrogen required. Fortunately, the end point farm gate price is very healthy this season as these nitrogen requirement numbers originally flabbergasted me.
No one really wants to pay for that amount of inorganic nitrogen in Urea or Anhydrous Ammonia needed to grow a legume crop, however our friendly little rhizobia bacteria can supply this basic building block of plant life, if we treat them right. Plus, the plants, much rather the rhizobia created nitrogen and perform or yield much better than the other inorganic nitrogen.
For our chickpea crop, its high protein seeds developed in our chickpea pods are what needs lots of nitrogen.
So, the hard slog of inoculating your chickpea planting seed is very worthwhile. Correct, many farmers have developed their own water injection process installed on the planter box or the olde backbreaking effort of mixing the inoculant on the bare seed in some mixer or conveyor belt. Water injection is infallible and prior to this point of time is a good goal to achieve.
I have been very keen on a new process where we are applying the correct Rhizobia strain of bacteria to the Mort and Co processed compost pellets and dropping a measured amount of these treated pellets into the seed trench.
Now, early trial days certainly suggest this much easier inoculation process is a good way forward, as my long-held belief is that we have many of our legume grain crops are growing short of nitrogen. If you look at those big numbers of required Nitrogen above, this critical soil nutrient must come from somewhere and if not in your soil profile and your inoculation procedure is poor, then where is the plant going to source it?
Believe it or not inorganic sources of N like Urea are not that legume plant friendly compared to properly active root nodules of live Rhizobia.
Live and active bacteria inside these healthy creamy white nodule lumps on the root system, are coloured reddish to pink internally. Other internal nodule colours like white or green are not active nodules and are not going to supply any plant available nitrogen.
So, there you have it. Nothing like another challenge in agriculture, however technology and our own creative ideas serve us well and easier and effective inoculation of our legume crops is one of them.
That’s all folks.