Mulching – with all sorts

Elizabeth Parker

Green Manures. In an experiment on an organic farm in the UK mulching with different green manures was compared using the yields from subsequently grown wheat crops to evaluate the effectiveness of the different green manures.

The plants used were three different leguminous green manures – Red Clover (Trifolium pratense L.), White Clover (Trifolium repens L.) and Trefoil (Medicago lupulina L.) and a non-leguminous rye-grass (Lolium spp.). All were cut at a height of 30-40 cm and left on the soil surface as a mulch. Over one year White Clover accumulated the most dry matter but Red Clover the most nitrogen (N). Both yielded more dry matter and N than the Trefoil and the Rye-grass.

The yields of the subsequently sown wheat varied. The spring sowings 6 and 18 months after green manuring yielded poorly but the winter wheat one year after green manuring yielded well when following both the Red and White Clover. Yields following the Trefoil and Rye-Grass were less good. It was concluded that overall Red Clover was the best species for use as a green manure.

Grass clippings. Experiments have been done in Sweden for 3 years on mulching cauliflowers with grass clippings. It was observed that grass mulching consistently resulted in increased yield and reduced damage by root maggots. The effects of grass mulching on root fly population was also studied for 1 year. The mulching did not reduce egg-laying but did result in increased egg-predation. The effects were most pronounced when the mulching material completely covered the ground even close to the stems of the plants.

Straw. Canadian horticulturists on Prince Edward Island have been experimenting to check that their traditional straw mulching of 4 t/ha was the optimum needed to significantly reduce cool season erosion. Mulching rates of 2, 4, 6 and 8 t/ha of straw on slopes of 5%, 7% and 9% were tried. Their results showed that sediment loss is significantly greater at 2 t/ha of straw than at 4 t/ha but that there is no advantage in sediment control above the traditional mulching rate of 4 t/ha.

Paper and paper sludge is a by-product of paper production. Experiments have been tried in the USA to determine whether raw or composted pulp and paper sludge was suitable for a soil addition or mulch for cottonwood plants. The primary sludge, by-products from bleached kraft and neutral sulfite semichemical paper was mixed with slaughterhouse paunch and 10% wood ash. Some was used raw, some composted in the field for 39 weeks. Both raw and composted sludge was applied as a mulch and incorporated into the soil. The plants were grown in a plastic house for 9 weeks before being planted out into the trial fields. After nine weeks plants grown on in fields with raw or composted sludge whether used as a mulch or incorporated in the soil improved in height by 40% and stem diameter by 20% compared with the plants in the non-mulched, non-amended control field. The optimum application rate was 135 Mg/ha.

Pine needles. During 1987-8 and 1989-90 researchers in India experimented with pine needles as a mulching material on crop yields on maize and wheat. The mulch was applied at the rate of 10 tonnes/ha just after sowing the crop. The results showed increased yields of maize (25%) and wheat ( 16%) compared with crops grown without mulching.


1. Dry matter and nitrogen accumulation by three leguminous green manure species and the yield of a following wheat crop in an organic production system
Stopes C, Millington S, Woodward L. Agriculture Ecosystems & Environment 1996 Vol S7 No 2-3, pp189-196

2. Mulching With grass clippings on cauliflower – effects on yield and brassica root flies Hellquist S, International Journal oi Pest Management 1996 Vol 14 No I pp39-46

(Reproduced with the permission of B O G Birmingham Organic Gardeners)