My Choice of Straw for Composting of Button Mushroom

The composting for the substrate production for the button mushroom involves selective breakdown of straw. In north India there is a choice among paddy straw, wheat straw, sugar cane bagasse and mustard straw.Each kind of material has its advantages as well as disadvantages.Each material is being discussed for its physical attributes, chemical composition and financial aspects.

Wheat Straw 

This is the most widely used material, the first choice of composting crew,but it is the most expensive too.The crop of wheat is harvested in the month of April and May.A big part of straw is also collected,chopped as fine material and stored.Then it is sold throughout the year as fodder for the cattle,mostly to the dairies as a popular cattle feed.The price is Rs2.50 to 3 per kg.after transport and unloading at the farm in Punjab, during harvest time, but keeps on increasing ,up to Rs 4 to 5 by September,and 6.50 to 7 by January. The moisture content during harvest time is 4% .During storage as the shining wax layer wane away, moisture can go up to 14%The straw is available in a blade size of 2 inches, and less,in length and mostly vertically splitted, as longer than this may hurt the palate of cattle.A large chunk of straw is burned by farmers who are too busy in harvesting and selling of grain.This is resulting in massive air pollution and loss of fertility of land.If the ban ordered by pollution boards is implemented, the straw collection would increase and prices may come down.

The bales of wheat straw with tubular structure, 12 inches long used in Europe,Australia and America are not available and no body makes bales with full length straw here.Therefore a moisture content of 75% at Fill Phase 2 may not be possible and 70 %to 72 % is fine.

Paddy Straw

The crop of paddy is harvested in the month of October and the paddy straw is available in plenty during October and November.The price is Rs 1.50 to Rs 2.50 per kg after chopping.The chopping can be done to any size.The moisture content is 10% to 15%.

Factors in Composting

Prewet As paddy straw do not posses a distinct wax coating like wheat straw,it absorb water as soon as it comes in contact with water.therefore the period of prewet is calculated by number of hours rather than number of days..The shining bright surface of fresh wheat straw is due to the wax layer, which makes the wheat plant disease resistant and help it to prevent excess loss of water. As soon as water comes in contact and stay, the bacteria come in action and dissolve it.

Level of fermentation Since the leaf to stem ratio is high in paddy straw, leafy material ferment faster than stem.This overfermented material makes the compost soggy and soft.This makes water management in the compost difficult.The formation of soft and buttery texture,if overfermented, is scary as such batches are not going to give optimum production.And how do we survive, if one has to pay the bank installment also, and average yield is less than 20%!

Structure of straw The outer layer is made of cellulose and hemicellulose, main source of Carbon. as the straw grow and turn from green to pale brown colour.This process can be compared to the building of a wall,where cellulose is the brick, hemicellulose is the cement sand mixture and lignin is reinforcement bar, making the straw hard.Leaves being soft have less of lignin.During the prewet and Phase 1,cellulose is decomposed and act as sponge and retain the water.Lignin is not touched and remain as such and is an excellent food for mushroom mycelium.

Chemical Composition of various kinds of Straw

From this chart,it is clear that lignin content is highest in the wheat straw. Lignin is responsible for maintaining its open texture during composting,so that air is easily passed through the heap of compost! Cellulose and hemicellulose wise, wheat straw score high.High silica in paddy straw only adds to high ash content which is of no use to mycelium.

Paddy straw is being used extensively and successfully where wheat straw is not available.The problem with paddy straw is its leafy soft material.Ideal condition would be to remove leafy material while chopping using a fan.Certain varieties of paddy are having less of leafy material and should be considered..Composting is shorter in duration.Water management should be tight which means that water should be increased gradually.It is easy to add water to a thirsty compost but not possible to extract excess of water out of it.Green straw should be avoided.Excess of goody water may not be used as it make the compost heavy! Adding Inorganic nitrogen like urea should be minimized as it would make the end products softer. It needs some experience as making paddy straw compost is relatively difficult compared to wheat straw compost. It may be filled in beds loose and is more suited to bed growing than bag growing.

Some farmers make compost by mixing wheat straw and paddy straw.Since the level of fermentation is different for the two materials, creating a uniform compost may not be possible.By the time wheat straw have softened enough, the paddy straw is over fermented making it sticky and soggy. Adding 10% of lengthy straw to short structure straw is a different game as we add it to give volume to the compost for better aeration, and not for the nutrition. 

Sugar cane bagasse

The bagasse available at most of the sugar mills is extremely  fine and is of no use.However bagasse from units making jaggery have a good texture.Raw bagasse cannot be used and must be cured till the sweat aroma is gone which may take over a month.Bagasse, being a tough material, composting period is relatively long.

Mustard straw

This is being used and again require a longer composting period.There is a lot of soil mixed in the material and interfere in composting.When straw is collected, the whole plant is uprooted from ground,and is collected by loader and soil with straw is inevitable.In the season it is available for Rs 2 per Kg at farm.For many years I did not try it thinking that unlike wheat, paddy, sugarcane and barley all belonging to grass family,mustard belong to legume family.But while working with this relatively tough material in a few commercial batches,I found it is promising.As the straw will be available in April next year,I hope to take few more batches to fine tune the procedure and compare the productivity..

Oat straw is too soft and corn stalks too hard!The straw of cotton and pulses is available in plenty and need exploration as ingredient of compost formulation.Can the yield match with wheat straw compost?Can it be cost effective ?Everybody should be questioning.

Conclusion

Wheat straw remains my favorite straw despite the high price.It is not so sensitive to water and to the number of days incomposting. By nature, it is more resilient and therefore easy to handle .After all, the profits in mushroom farming comes from the higher yield and not by cost cutting by compromising on the quality of raw materials. However a good composting person would understand the nature, age and quality of straw made available, adapt the water management,time duration of prewet and Phase 1, level of fermentation and formulations to make a productive compost.

Emerging First Flush of button mushroom