Green Manure/Field Beans - Update

 In a previous post, I reported on the use of field beans as a green manure.

Photo 1: Podded Field Beans

We have now gathered in the crop, eaten some and blanched/frozen the rest. I will be growing beetroot, parsnip and turnip in their place.

Green manures serve a number of purposes including retaining and adding nutrients, minimising soil erosion, increasing organic carbon content and weed suppression. Field beans achieved all these objectives and, in addition, provided an edible crop. They also kept the plot free of cat muck which is definitely a plus!

I planted the beans approximately 10 cm apart in rows 10 cm apart in a plot measuring approximately 1.6 metres by 2.2 metres. For an outlay of about £2.50 (500g field beans from SowSeeds cost £5.55 and I used about half of them). I did not irrigate or fertilize the crop. This small plot of 3.5 m² yielded 4.8 kg of podded beans.

Frozen broad beans are currently on sale at £2.60/kg, so the nominal value of my crop is £12.50; an investment return of 500% over six months ((I've ignored my labour costs but then I've also ignored the other benefits such as soil improvement, reduced weeding time and less cat muck to dispose of).

Since my 3.5 m² plot equates to 0.00035 hectares or 0.00086 acres, I can reformulate my crop yields as either 13.7 tonnes/hectare or 5.5 tonnes/acre (note: 1 tonne = 1000 kg).

Field beans grown commercially have yields of 2 - 4 tonnes per hectare, with autumn-sown beans at the lower end and spring-sown beans at the upper end. Field bean yields are double those of broad beans. The Bean Yield Challenge is aiming to produce yields of 10 tonne/hectare or more - the current record is 8.32 tonne/hectare.

Not wanting to brag but my 13.7 tonne/hectare is presumably a world record and I claim my prize! OK, maybe there is a minimum field size and I do not qualify. However, it does demonstrate the yield advantage that small market gardens have over large-scale commercial farms.