ILEIA Newsletter Vol. 11 No. 3 p. 16

Green manures, a new chance for small farmers

Valdemar Hercilio de Freitas

After severe soil degradation and increase in fertiliser prices, small farmers in Santa Catarina, South Brasil, supported by EPAGRI (Empresa de Pesquisa Agropecuária e Extensâo Rural) and other research and extension agencies, succeeded to develop and propagate green manure/cover crop technology on a large scale. Results are impressive: higher yields, weed control, lower labour need and a halt to soil erosion.

The farming conditions of Santa Catarina state, combined with the predominance of soils highly susceptible to erosion and with intensive soil movement through ploughing and harrowing, have led to a high degree of degradation of natural resources. The development of the so-called "commercial input" has worsened this critical situation.

It was only after the oil crisis, the increase of fertiliser prices and supression of government intervention, that Santa Catarina farmers, together with Agricultural Research and Extension, began to search for new alternatives of adequate soil use that could minimize the dependence on external factors and aggregate the use of local resources. This in turn would affect production costs, increase yields and reduce risks of environmental degradation.

Green manures widely accepted

Together with the State Agricultural Research and Extension Services, Cooperatives, and Private Organisations associated with tobacco production, EPAGRI propagated the reuse of green manure/cover crop technology among all state regions. Farmers’ experimentation with several green manure species was widely stimulated.

Thus, green manure/cover crops began to be used and adapted to the different production systems existing on farms. A recent survey carried out by EPAGRI shows that, at present, more than 300,000 ha are cultivated with some kind of green manure crop, involving more than 100,000 farmers. At present the following summer green manure crops are being preferred by farmers.

Summer green manure crops

• White mucuna Stizolobium niveum

• Black mucuna Stizolobium atterrimum

• Stained and Dwarf Mucuna Stizolobium deeringianum

• Crotalarias: Crotalaria mucronata, Crotalaria spectabilis, Crotalria juncea, Crotalaria retusa, Crotalaria grantiana

• Jack bean Canavalia ensiformis

• Pigeon pea and dwarf pigeon pea Cajanus cajan

The summer crop leguminous species, primarily Mucunas and Crotalarias, are generally planted inbetween rows of corn and tobacco. After harvesting the main crops, the green manure crops quickly develop, protecting the soil against rain and solar radiation. In the winter and in areas affected by frost, these species dry out naturally and the respective residues (straw) protect soil until the summer commercial crops are planted.

Where green manure plants do not collapse and dry out because of cold weather, they are cut and used as mulch, through the use of cultivators, harrows, disk-rollers, or even cut manually. Planting of summer crops is either done through incorporating the dry mass produced or through adopting a soil conservation approach including either minimum tillage or no-tillage. Beside summer green manures also winter green manures are being used.

Winter green manure crops

Grass plants:

• Black Oat Avena stringosa

• Italian ryegrass Lolium multiflorum

• Rye Cecale cereale

Legume plants:

• Common vetch Vicia spp.

• Hairy vetch Vicia vilosa

• Chicaro or xinxo Lathyrus sativus

• Fodder pea Pisum sativum, var. arvernse

Cariofilacea:

• Gorga or spergula Spergula arvensis

Cruciferae:

• Fodder turnip Raphanus sativus, var. oleiferus

These green manure/cover crops are used at a season (winter) in which most of the small farmers have no choice of using the soil for commercial crops, except for wheat. Most of the farmers incorporated the green manure or the crop residues (straw) into the soil through animal or mechanically driven ploughs. At present, there are more than 120,000 ha cultivated with minimum- and no-tillage systems.

Minimum-tillage

Minimum-tillage is the most popular system among small farms that use animal power (basically oxen), and among farmers that plant corn and tobacco. In this system, furrows are opened in the layer of green manure plants in the final stage of their cycle (spergula, vicia), in the layer of straw produced after lodging, or in the layer of crop residues (wheat). The furrows are made at specific intervals according to the desired spacing, and to the use of equipment already existing on the farm.

In the case of onion, the most common system is minimum-tillage using adapted tractors. The rotary hoes are replaced for a kit developed by local farmers, which is at present available on the market. Although many herbicides are still used in this system, the last 4-5 year experience demonstrates that herbicide use can be significantly reduced.

The minimum-tillage system allows for effective erosion control, a continous supply of fresh organic matter on the soil, and it is time and labour saving, mainly at the planting season. Weed control, if necessary, is performed in planting furrows, using animal driven equipment. The increased soil fertility is reflected in fertiliser saving, mainly on nitrogen fertilisers.

No-tillage

No-tillage started to be adopted by small farmers, usually in maize cultivation, as soon as machines and equipment were adapted to this system. There was intensive participation of farmers in experimenting and adapting these machines, thus characterising a concrete example of "Participatory Technology Development". Where mechanical traction (tractors) predominates, the use of herbicides has increased, mainly because the areas are extremely infested by weeds, due to consecutive years of plowing and harrowing.

Nevertheless, small farmers have been adopting no-tillage for many years now, showing that it is perfectly well possible to use no-tillage with no or limited use of herbicides. These farmers work on heavily sloping lands with extremely simple equipment. They do not depend on mineral fertilisers in specific crops, having low costs and excellent yields.

The farm of Mr. Ristow

The farm of Mr. Roland Ristow provides a good example. The farm of this 66 year old small farmer in the municipality of Ibirama measures 20 ha. Only 5.1 ha are devoted to annual crops (maize, tobacco). The remaining land is dedicated to native woods reforestation and pastures. In parts of the area used for annual crops the slope varies between 20%-45%.

Mr. Ristow has used mucuna Stizolobium niveum and S. aterrimum in natural combination with papua grass Brachiaria plantaginea for 35 years, although he has only practised no-tillage since 1980. In order to arrive at an ideal system he had to develop a special machine to lodge mucuna and brachiaria biomass. This consisted of an adapted microtractor combined to a 4-disk roller mounted forwards.

Whenever heavy frosts occur, the use of this equipment is not necessary, because lodging and drying is performed naturally. Tobacco planting is carried out manually and maize is planted by a handheld machine called saraqua. Mucuna is sown all year round, the seeds are produced on the farm. He uses corn seed variety "EPAGRI 351-Conda", because with this there is no need to renew the seed every year.

Results obtained are outstanding

• Without using any mineral fertiliser Mr. Ristow obtains 5100 kg of maize per ha, compared to 2800 kg on average in the region;

• Labour used in no-tillage is only 1/3 of that used in conventional systems;

• No-tillage permits a total control of "competing plants". When brachiaria develops in excess, it requires some weeding. But when pests and diseases occur they hardly ever produce economical harms;

• Under the slopy and no-tillage conditions there is no evidence of erosion on the fields. This can be easily observed if we walk along the paths in the middle of the farm.

Mr. Roland Ristow thinks that "both large and small farmers that do not conserve the soil will disappear within 20 years time. Only those who use organic fertilisation and who have some ecological and environmental awareness will remain!"

Valdemar Hercilio de Freitas, EPAGRI, CP 502, Itacorubi, Florianópolis, Santa Catarina, Brazil.

This article is a translation of: O uso e manejo de adubos verdes no estado de Santa Catarina – Regiâo Sul do Brasil. In: Revista Pecuária Catarinense Vol. 8 No.2 (Junho 1995).

References
– Calegari A. et al. 1993. Adubacâo verde no Sul do Brasil. 2da Edicâo. Rio de Janeiro, AS-PTA.
– Monegat C. 1991. Plantas de cobertura do sols: caracteristicas e manejo em pequenas propriedadas. Chapecó, Santa Catarina, 337 pp.

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