Natural (Bio)fertilisers & Living Mulches: The Edible Legumes

I have been running several posts on using plants as biofertilisers, living mulch and even chicken feed. This post is a follow up on the living mulches that I have been experimenting with. Several plants (which include many legumes) that can be used as green manures and green chicken forage.

Previously, I have used Penny Royal to keep weeds at bay in The Weed Zones that border the vegetable plots – but I wanted a living mulch to plant inside the vegetable plots as well. Preferably a legume to fix nitrogen and release the nutrients once it dies off (legumes do not share their nitrogen when alive!). It must, however, still be a ground cover so that it doesn’t out compete the vegetables for light… hence after some research and looking at what is available in the nurseries – I had two choices: Red clover or White clover.

The other idea I had was, once I had big patches of clover (and if I needed to uproot some to plant new veggies) I could move the extra plants to the alfalfa patch – this allows more green forage for the chickens in winter. I also hoped to find both species so that I can have more diversity in the garden, but unfornutately the nurseries only stocked white clover.

The white clover (Trifolium repens) I acquired is a black cultivar sold under “Black Shamrock”. It did a little poorly when I just transplanted it (winter last year) – it was a bit sickly, had chocolate spot fungal problems (a common infection for legumes so watch for signs on peas & beans!). It had a tough time during summer as well (very hot last season) – but it established and grew like a beast this last winter. The penny royal had died off in some areas during the last winter, which the white clover has encroached on – doesn’t bother me either way… Here it is with it adorable white flower heads!

Clover and alfalfa flowers Trifolium reprens dubium Meticago sativa seeds lucerne comparison difference — Similar flowering structures of legumes in the vegetable garden.

A ‘wild’ clover had made its way into my vegetable garden during the same time I transplanted the others. I noticed the subtle similarities in flower and leaf structure between the two. I took to some digging around the Internet dungeons to find that it was, Trifolium dubium (lesser hop trefoil or tick trefoil!). It has a less compact growth and its low branches spread outwards from a single plant. It carries a small cluster of yellow flowers and self seeds remarkably easily. The yellow clover has an additional bonus – it is more drought and heat tolerant than the white clover. By some selective weeding between the sour sobs (Oxalis sp.), which look very similar especially as seedlings, I managed to get a good patch going. The seeds of the lesser hop trefoil (lets call it yellow clover for simplicity) is ripe when they turn completely black – you pick them off an sow somewhere else (likely only germinate in warm weather) or leave to self seed.

Clover Sour sob Kidney weed Trifolium Oxalis Dichondra leaf leaves comparison difference — Similar looking weeds that grow naturally in the vegetable garden and how to distinguish from clover species

Whilst I was reading up on literature for my research project, I glanced over some articles pertaining to nitrogen fixation in alfalfa and clover. Legumes associate with certain bacteria in the soil, which infiltrate the roots and form nodules – this is where nitrogen is created and accessed by the plant. It is only during the death of these nodules that the nitrogen is released (along with the bacteria) into the soil. Interestingly I read that the bacterium associated with Soybeans is not native to South African soils and needs to be added to the soil by farmers through special liquid fertilisers! Here is a list of legumes I grow and their associated bacteria:

Legume	Species bacteria (bv. = biovar)
Pea	Rhizobium leguminosarum bv. viciae
Bean	Rhizobium leguminosarum bv. phaseoli
Alfalfa	Sinorhizobium meliloti
Clover	Rhizobium leguminosarum bv trifolii

All these above-mentioned legumes are not native to South Africa, but in some areas due to their widespread cultivation; natural and on-going population have become established in the soil. Also if you are fortunate enough to get seed inoculated with the bacteria there is a good chance for the plant to establish its own nodulating population. So this lead to some digging into whether or not my legumes would develop any nodules in order to fix nitrogen. Hence, some investigation! I promptly gathered up my camera and some digging tools and set out to the veg garden. I dug up each plant and recorded the nodule formation.

Lesser hop trefoil Trifolium dubium nodule — Yellow Clover nodules, be careful to uproot as nodules break off easily!

Legume root nodules pea soybean bean alfalfa clover comparison difference sizes — Images of legume roots and their nodule formation. Longest nodules are indicated by the orange circles.

As you will notice the Peas and Beans have minuscule to no nodules, meaning that my soil lacks Rhizobium leguminosarum bv. viciae and Rhizobium leguminosarum bv. phaseoli. Therefore organic fertilisers are required to supply the Peas and Beans with enough nitrogen for healthy growth. The alfalfa and clover however are a different story – just look at the lovely nodules! Therefore both the clover and the alfalfa are generating nitrogen. Thus, during the death of the plants nitrogen is released back into the soil. The alfalfa plants are a permanent stand and would likely not release any nitrogen into the soil (they have many other soil building properties however), but the clover dies and resprouts the whole time. Therefore, each generation of clover helps build up the soil nitrogen! How cool is that?!

Since the establishment of my weed barriers and biofertilising crops for about three years now; the garden is (almost) weed free and with the help of the clovers my vegetable garden’s soil should drastically improve over each successive clover crop. Therefore, legumes are an essential tool for organic gardeners by taking advantage of it being a living mulch, biofertiliser and chicken forage crop!

Now then – here is a sneak peak to my on-going experiment – Peanuts! Just look at them nodules (Bradyrhizobium yuaminhense & B. elkanii, about 22 Bradyrihzobium spp. that associated with peanuts are native to South African soils)!!! I added a picture of Soybean nodules (from Bradyrhizobium japonica inoculated soils and not from my garden) – forgot about measuring, but if I recall correctly they were anything from 1 cm to 3 cm. This is what healthy pea and bean nodules should look like too!