How do you grow enough of your own mulch in order to establish thousands of newly planted trees and shrubs? That's one of the design goals we're attempting to meet for a 5 ha forest farm currently under development at Balkan Ecology Project in Bulgaria.
The farm is essentially an agroforestry system comprised of mixed species fruit trees, soft fruits and nitrogen fixing shrubs planted in 'rows', under-storied with support plants, herbs and perennial vegetables. Between the rows are the 'alleys'. The alleys have potential to be used for growing hay, cereals, vegetables or rearing pasture raised poultry such as chickens or turkeys.
The alley cropping site design
What the mulch is for?
There will be 2,553 trees and shrubs planted across the site. The mulch will be needed for the first five years while the plants establish, and will conserve water, prevent weed competition and improve soil quality as the mulch slowly decomposes over the seasons. For the first five years the alley space will be dedicated to growing this mulch. After the fifth year when the trees and shrubs no longer require mulch the plan is to use the alleys for pasturing poultry.
The farm development has already begun and this year the soil improving cover crops were sown across the site to prepare the soil for planting. The trees are scheduled to be planted in the autumn and spring.
Normally for bulk mulch one would use straw, wood chips or compost (in a cool climate). For the first year we will be using straw, but I'm very interested in finding an on site solution for mulch production, and believe we should be able to supply the bulk of the mulch needed by cultivating grasses in the alleys.
What plants are best suited for mulch production?
Below are the plants subsequently selected for sowing in the alleys.
When and How to Harvest the Mulch
At this location June is the wettest month of the year, with July and August being the driest. Therefore I am planning for a mulch application every June following a heavy rain so that the ground is well soaked and the mulch can conserve the soil water and prohibit weed growth from competing with crops during the dry summer months. The mulch from the initial autumn planting should still be in place, although by June some plants will be making their way through the mulch. These plants will be pulled and applied to the surface along with the new mulch.
The mulch will be cut using a sickle bar tractor implement of 2.3m width that can be attached to a compact utility tractor such as a John Deere 3250. Two passes with the sickle bar will leave a strip uncut that is left to provide extra habitat for beneficial invertebrates such as spiders and ground beetles. The strip can be cut every two years on alternate sides of the alley.
Grasses running into rows
Seed dispersal from second cuts
It is unclear to me how fast the plants will flower following the first cut. It could be that with water stress kicking in during the summer the regrowth will bolt to seed. Close observation is required here and the second cut may have to be used for hay or hot compost to prevent seed dispersal.
Calculating how much mulch you need and how much mulch you can produce
Based on average data from local sources I have estimated that an average of 0.60kg per m2 (dried weight) can be harvested in a year. This includes two cuts being made per year.
The weight of a standard square bale = 19kg (based on an average dried weight of a bale) so it takes and area of 31.6m2 to grow enough vegetation to make 1 bale.
The area we have on the site for mulch growing is as follows:
Alleys = 16112m2 = 510 bales
Meadow = 1846m2 = 55 bales
Total bale production = 565
Using a third of a bale for each plant will cover 1,695 plants which leaves us 858 plants still needing mulch. Mowings from the Inter Alleys (see diagram below) may also be used and we'll be experimenting with a 600m2 patch of Robinia psuedoacacia runners that will be mowed twice a year, when the growth is still soft and herbaceous, and see what biomass we receive from this.
We'll make up any shortfalls from spoiled straw and municipality green waste.