How to check for nodulation and the Nodulation Chart

Floyd Sullivan, Business Development Manager, ALOSCA Technologies Pty Ltd

Now is the time for digging up your crop/pasture legumes to check the nodulation.

Use this nodule rating system. This is the system used by the Centre for Rhizobium Studies (CRS) at Murdoch University www.crs.murdoch.edu.au to assess their field samples. The chart was supplied courtesy of the CRS.

Nodule scoring system.

Remember when sampling

1. Timing, don’t expect to see many nodules before 6 weeks post germination. Also be wary of later season nodulation assessment as nodules will senesce as soils seasonally dry out in spring.

2. Take a representative sample, much like you would for soil sampling. You will need a minimum of 20 plants, the more the better.

3. Dig plants up don’t pull them out. Even in light textured soils nodules will pull away from the roots if pulled from the ground. Dig down most of a spade blade depth if possible (250mm).

4. Wash the soil from the roots. This is particularly important with heavier textured clay and loam soils. With light textured soils the bulk of the dug soil will fall away and a light rinse will reveal the nodules. Heavy textured soils can be a little problematic when washing and may require soaking in a bucket of water for a while to disperse the soil before you can assess the nodule colonies.

5. When assessing the root nodules there are 2 main attributes you should be assessing to give you an idea of how efficient your legume-Rhizobium nitrogen capture is or is progressing if it is an early assessment.

6. Firstly nodule number, use the nodule rating system to rank your sampled plants on the 0-10 scale by grouping the plants into piles. Tally the plants in each segregation. The tally totals can be used to calculate percentages and/or a whole of sample average. Secondly assess nodule colour, you will need a sharp blade to cut nodules open and check they are pink inside. If the nodules are green or brown or white then they will in all likelihood be ineffective nodule colonies not optimally fixing nitrogen. There can be effective and ineffective nodules on the one plant.