1 Some people working in the field (such as Stocking (1985)) have stated that the only long term solution to soil erosion is vegetative protection & fertility.

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Some people working in the field (such as Stocking (1985)) have stated that the only long term solution to soil erosion is vegetative protection & fertility enhancing farming systems rather than mechanised methods.

- debatable for drought prone areas - water conservation extremely important - usually requires some structures.

best approach = holistic one which combines various methods.

AGRONOMIC AND VEGETATIVE ASPECTS

Introduction

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Reinforcement of soilIn addition to protecting the soil from raindrop impact, plant roots also help to anchor the soil in place.

Roots & rhizomes have a relatively high tensile strength and adhesion (soil to roots) and when these are embedded in a soil matrix having low tensile strength soil, the shear strength of soil is enhanced (cf. reinforced concrete).

Fine roots most effective :-• grasses down to 1.5 m, • trees down to 3 m.

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Organic matter

increases infiltration

rates debris slows overland

flow

increases water

holding capacity

debristraps silt

recycles nutrients

mulchfrom

residues

Effects of organic matter from plants

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Soil preparation aspects

Ploughing

• aim for large clods to maximise roughness, as this improves porosity & infiltration and temporary surface storage

• deep ploughing often inadvisable as subsoil may be unstable or infertile - best not to bring subsoil to surface so usually adopt 15 cm maximum depth for mouldboard ploughs - can be deeper for disk ploughs which do not invert the soil

• pans can develop if soil is ploughed with heavy equipment when wet

- may decrease infiltration and increase runoff as well as causing waterlogging - in mechanised conditions, ripping may be necessaary

/possible

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7• early ploughing may cause oxidation of organic matter if soil inverted

• best time to plough is at end of harvest when there is still some soil moisture but often this is time for celebrations and there is "no time" for ploughing;

• if post-harvest ploughing can be carried out, moisture can build up from occasional showers in dry season and at start of rainy season

• many soils become very hard in dry season

• otherwise may have to wait until after rains - especially if hand cultivation- wastes time

• if ploughed before the rain, oxen or tractors usually necessary but even these may not have enough draught power

• increased risks of soil erosion after harvest ploughing especially on steep land

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• tractor ploughing on contour limited to 17% for 2WD vehicles, 25% for 4WD.

Contour ploughing

• for permeable soils, plough along "exact" contour;

• for very impermeable soils, plough at angle to contour with slope of 0.25 to 0.5 to encourage drainage

• permanently mark contour or plough direction by planting trees

• can be mechanised, semi-mechanised or hand cultivation;

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• when it rains, harrowed soil may experience reduction in infiltration rate caused by crusting

Harrowing

• best timing is just before planting to avoid erosion caused by effect of rain on very loose soil

• size of tilth is important; ideal is to achieve same average aggregate size as seed size

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• Compaction is usually deleterious but may have beneficial effects on some loose textured soils. AWC and engineering properties may be increased – e.g. forested road embankments – balance needed

Compaction

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• some (maize?) varieties can be planted up to 15 cm deep - seeds wait for rain to percolate down, by which time, there is more confidence that rains have started.

Depth of planting

• plant too shallow and seed dries out - too deep and seedling cannot emerge; 25 to 50 mm typical – maize up to 100 mm if dry soil – deeper in light soils than heavier soils

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• Also helps to maintain porosity and infiltration rate increases brought about by ploughing.

Time of planting

General principles

• Early establishment of crop canopy will help to absorb raindrop energy early in season and so reduce splash erosion and surface sealing.

• Early establishment makes best use of available rain.

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• increased weed problem (as crop & weeds germinate at the same time)

Dry planting

• makes optimum use of early rain• spreads work load

• agroclimatic analysis to determine best (called "trigger") dates very important

Risks and problems:• large variation in start date for rain from year to year

• if rain late, seed can be lost and so replanting will be required (but will seed be available?)

• animals (e.g. ground squirrels) may eat dry seed so guards may be necessary• delay in replanting waiting for rain to "re-start" may lower eventual yield

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• Usually wastes rain & time (i.e. reduces possible growing period (often correlated with yield) )

Plant after start of rain

• May be essential on hard soils especially cultivation is done with digging stick or hand hoe

• Avoids weed problem of above , weeds germinate first then hoed

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• leads to increased risk of pest damage (pests that only feed on the crop at certain stages can proceed to the next "phase" as it becomes ready to eat)

Phased planting

• Plant part of field/farm then later on (after a week?) plant next part

• leads to lack of uniformity

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• Symbiosis: second crop may fix nitrogen that can be used by first crop, first crop provides shade to second crop, first crop may provide physical support - not the same as parasitism which implies feeding or using moisture, each may help prevent spread of pests to the other)

Relay or sequence planting

• Plant second crop underneath first crop before first is harvested so that it gets off to a good start

• Grows up through first crop

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Other factors affecting time of planting

• Birds / pests may arrive at certain time & may be best to avoid having grain ready at that time even if late planting means yield is less than ideal (with no pests or under experimental conditions)

• Air temperatures affect soil temperatures and these affect mineralisation of N - avoid high temperatures at times when crop susceptible to nitrogen supply

• Radiation varies throughout year according to angle of sun. This has direct affect on potential for photosynthesis

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• Fungus similarly (e.g. millet more susceptible to "smut" if it flowers in heavy rain)

• Weed growth may be at a maximum at a certain time of year - avoid maximum weed growth when crop most susceptible to (e.g.) moisture supply if possible.

• Crop physiology may require avoidance of rain or drought at certain stages of growth

• Viruses may only attack under certain climatic conditions (e.g. groundnuts will suffer from mosaic virus if planted late)

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Response farming

Experiments have been conducted in semi-arid East Africa(e.g. Stewart & Faught, 1984) to find best management regime for very variable rainfall conditions by estimating total rainfall on the performance “so far”.

Experiments were aimed at being able to provide low risk guidelines using radio/extension workers to pass information on to farmers, based on the accumulated climatic conditions since the crops were planted.

This approach is called response farming

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(iii) at 75 days - can predict harvest - alert govt. etc. re. famine if necessary

Example for maize:

(i) Early start to rain was correlated with higher seasonal expectation of rain. So if early start to rain advise farmers to:· use high seed rates & fertilisers· plant higher proportion of drought susceptible (usually more valuable) crops

Use opposite strategy if rains start late.

(ii) After 40 to 50 days, advice on thinning schedule is again based on climate so far; may need to decide on whether or not to plant catch crops such as cowpeas

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Optimists - aim at high production and are prepared to thin or remove alternate rows if season has low rainfall

Pessimists - aim low, but add nitrogen, relay sow, plant short season -inter-crop or catch crop if rainfall is better than feared

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This measure is also used for different cultivation systems such as shifting cultivation. NB if 1 yr in 5, R = 20%; 5 yrs in 25 = 20% also, but production and erosion may be different

Fallowing and rotations

Theory is that nutrients, organic matter and water build up during year or season, then these are released and become available for following years crop.Break in disease or insect pest cycles.

100x(%)R fallow +n cultivatiounder Yearsncultivatiounder Years

Return period R is defined as:

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Types

Shifting cultivationR factor < 0.3 (R < 30%)

Jhum cultivation system in MEGHALAYA India

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• plough field then leave for a year without planting• weed during year to reduce evaporation• yields in experimental conditions have been up to 4 times• without fallow• unpopular with farmers; difficult to convince them to weed • unplanted fields!• technique also advocated for nematode control

Weed free fallow

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1st season fallow

leave field unplanted in first season, plant in second when moisture has built up

in experiments, yields have been double (second season crops)

depends on having suitable (bimodal) rainfall distribution

a variation of this is to leave land fallow in hot, rainy season so that moisture can be built up for dry, cold season crop as is done on vertisols in N. Nigeria (see earlier note)

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Partial fallow

in first season, plant with crop having low water use requirement, e.g. E. teff, proso millet

technique may not be effective in cracking soils with high available water capacities in surface horizon as subsoil may remain dry, then in second season, what little moisture there is in sub-soil evaporates directly to atmosphere

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Effect of soil fertility and rainfall on return period R% for maintenance of nutrient levels adapted from Table 12 in Agrofor for SC

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more fertile soils can be cultivated for a larger percentage of the time

with high inputs, land can be cultivated for a larger percentage of the time (though not 100%)

heavier rainfall areas leach nutrients more quickly so have to be rested more frequently or have more inputs

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Minimum (conservation) tillage

Spectrum of meanings from:

machines to plant through stubble then use herbicides to kill weeds –GM soya (for example) to resist herbicide

TO

burn weeds then dig holes and hand plant

rainfall is low so weed growth in dry season is small

soil may become very hard so runoff may be high – system could be improved by in situ water harvesting

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Need to note the following points:

• Soils with low flora & fauna activity such as in dry areas may be unstable and have poor structure. Such soils probably benefit from tillage for improvement of infiltration & root penetration

• Herbicides are too expensive for lower income countries

• Results have been disappointing, e.g. in N. Ghana, it was found that minimum tillage was not as effective as ridging, mulching, or even traditional mixed cropping. More research required.

• Analyse each situation independently

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Intercropping & mixed cropping

Difference between intercropping and mixed cropping

Advantages

Depresses weed growth

Increased return / unit area (but probably not if stressed due to water shortage)

Reduced lodging

Reduced soil erosion because of better ground cover

Legume intercrop increases soil fertility (N producing bacteria) and improves neighbouring crop

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More efficient use of available water (e.g. Ikeorgu, 1987)

Insurance (pests, diseases & drought may affect one crop but not the other)

Shading effect often beneficial (e.g. coffee shaded by bananas)

More difficult for disease to spread especially in case of intercropping

Sometimes an ad hoc mixed cropping system is adopted in which farmers fill in gaps in crops planted earlier which have failed to establish well

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Disadvantages

System is difficult to manage, i.e. to decide on relative mix and spacing

There may be negative (i.e. competition) as well as positive interactions. The situation is complex.

There is some doubt about the benefits of its adoption in lower rainfall semi-arid areas

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Examples of complex intercropping practices in eastern Gujarat, India

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Growing crops in dry season on residual moisture

It is sometimes possible to plant a crop at the end of the rainy season that is capable of growing on residual moisture possibly combined with light rain in a second (usually shorter) rainy season [if there is a bimodal distribution]

Examples from India are shown in the diagram.

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Mulching

Stubble mulch

needs a lot, e.g. 10 tons/acre is typical; 5 t/ha for straw/crop residue mulches is a common recommendation

termites may eat it but if that encourages termite activity in soil also they will benefit the soil by inducing increased infiltration

stubble absorbs water rather than allowing it to infiltrate; later evaporates directly

may increase disease risk, there is a need for frequent inspection

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crop residue is often needed for feeding to animals especially if used for ploughing

incorporation of residue may depress N at critical time

sometimes removed weeds are used; left on surface between crop rows

can reduce weed growth by preventing sunlight reaching surface

greatly reduces runoff so mulch is good for soil conservation

can reduce splash erosion e.g. Sesbania sesban prunings used @ 5t/ha combined with 50 kg P/ha 1 to 4 weeks before planting, or after planting (but not at planting)

for e.g. from IITA, see following table

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Grass mulch

1 to 4 t/ha a typical recommendation

may be difficult for farmers to obtain - conflict with fodder requirements

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Dust mulch

works on basis that unsaturated hydraulic conductivity of course pores is lower than that of finer pores

dust produced by tillage

increases erosion risk

there is some evidence of negative effects on water availability & reduction of evaporation

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Gravel mulch

very expensive, only used in horticulture

occasionally, there are naturally occurring gravely soils which local farmers recognise as reducing soil evaporation.

Surface stones are a problem for cultivation, but there may be advantages too. Possibly use large stones only for stone bunds and leave smaller stones on surface but many workers recommend that stone bunds should have a grade of sizes from large to small to improve filtering capacity

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Others

e.g. Vermiculite, ash, sand, sawdust, bark

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Soil nutrition

Erosion has a great effect on soil nutrition - and vice versa. Hudson said that a bag of fertiliser may control erosion better than a physical structure

The concentration of nutrients in eroded soil is usually higher than the soil from which it was eroded.

The ratio is known as the “Enrichment factor” which is of course a misnomer, “impoverishment factor” may be better. For Kenyan soils, the ratios are in the following ranges:

1.1 to 2.1 for P

1.1 to 2.8 for Ca

1.1 to 3.0 for Mg

1 to 2.3 for K

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10 t/ha/yr of eroded soil

may be equivalent to

40 kg N/ha/yr (2 bags).

In Zimbabwe, 30 t/ha/yr of eroded soil = 50 kg N/ha/yr plus 5 kg P2O5

[with a replacement cost of $20 to $50]

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Effect of soil erosion is hidden in many temperate region countries. Option of soil mining, with massive replacement of nutrients may not be open to many farmers in LDCs.

Rapid early growth and good cover is desirable for Soil Conservation, so irrespective of yield, adding fertiliser may be beneficial

Drought will usually suppress benefits of application of N (e.g. Chinene & Pauwelyn, 1987)…..

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Am

ount of N

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May also reduce yields (because of effect of increased vegetative growth)

Many farmers only apply fertiliser if there has been a significant amount of rain in order to ensure that an adequate cost/benefit ratio is obtained.

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Typical annual losses of soil, rainfall, and nutrients from farmlands (Zimbabwe)

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Biofertilisers

blue-green algae/Azolla spp.

grow from “seed”; water and add fertiliser

adds OM and N to soil

cheap but some labour requirements (claimed to be small).

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EPIC

Erosion Productivity Impact Calculator is a sophisticated erosion model which takes account of the “enrichment factor”

Some conclusions reached using EPIC in Kenya were:

crop losses in tropical soils are 2 to 3 times higher than in temperate soils for same amount of soil loss

yield loss greater for first 10 - 20 cm of soil, possibly as much as 75%

yield decline, in absolute terms, greatest for erosion on highly weathered "old" soils with high OM

yield decline in % terms > for soils with initially low fertility

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Green manuring

increases O.M.

increases infiltration and so brings about an increase in soil moisture

also increases soil N if legumes are planted

e.g. Crotalaria in Tanzania: C. ochroleuca @ seeding rate of 10kg/ac; cut when 30 cm high to allow regrowth Used as fodder. C. juncea is also used.

some query about economics in semi-arid areas

increasing problem with land availability

preseason crops for rice in India

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Crop spacing

To improve production, spacing inversely proportional to aridity.

But may be better to accept lower yields and higher densities for Soil Conservation.

Farmers may over-plant to allow for losses from drought or pests.

In India, purposely over-planted to obtain thinnings to feed to cattle

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Crop management

e.g., poor pruning of tea leads to poor cover, which in turn causes increased erosion

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More on trees and hedges

Hedges, shelter belts, agroforestry systems (e.g. alley cropping), fruit trees, MPTS, (may!) all help – system approach not trees alone

Shelter belts will be discussed in more detail later in context of wind erosion

Traditional cut thorn hedges should be discouraged. They do not reduce erosion significantly. Broken branches should be used for firewood, not hedges. Grow hedges instead.

Small field sizes preferable where soil erosion is a problem – hedges – but potential social problems

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Benefits of hedges directly affecting SWC:

reduce saltation processes better than trees.

also reduce runoff because of litter

hedges are almost indestructible yet permeable, but very little hard data on contribution to soil conservation

can be used to help control cattle grazing and damaging structures

hedges made of brushwood, palm fronds sometimes used to reduce evaporation &/or wind erosion as well as marking property

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Trees in general may

help anchor soil in place if used as part of a systems approach

help to reduce wind erosion if part of properly designed shelterbelt

may reduce crop evaporation by providing shade and reducing wind velocity

mulching effect of litter - protection against soil erosion; increased infiltration rates

provide nitrogen in leaf fall which may become available for crops

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Other benefits:

May provide fodder, fuel, fruit,

May fix N

fruit or nut trees may justify cost of water harvesting

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Disadvantages:

tree canopy does not necessarily reduce erosion; may increase it on degraded land; ambivalent effects esp. in semi-arid areas. Erosion is often seen under trees (e.g. animals like shade so preferentially grazed, also leaf drainage;

low bushes more effective than high canopies unless a multi-story forest or tree-bush-crop system is being established

under adverse climate, slope, soil conditions, agroforestry may not have a significant impact

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Management:

need for protection

surface cover of > 60% by herbaceous plants, litter, prunings or mulch should be objective

can be used to establish terraces, use terrace spacing formulae in the absence of other research [W = 100/S [W (m); S in degrees]]; decrease spacing between rows with slope

alley cropping

?? goats eat trees because man has degraded the environment and other livestock have a problem surviving; goats do not cause deserts, people do

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read handout on contribution of deforestation

to runoff and erosion

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Weeds

Competition from weeds means best use of available water is not being made

Worst for young crops (competition for water & nutrients)

Weeding often done by hand, usually by women & children

labour is a major bottleneck for most subsistence farming. May use 40% to 60% of total labour on weeding

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sometimes it is recommended to let weeds grow after 1st rains, then plough & plant - over 80% reduction in labour may result using this technique

or - commence 4 to 6 weeks after planting & follow-up @ flowering / reproductive stage of weeds

Post - harvest tillage kills weeds & as well as helping to builds up store of moisture

main point is that timing of weeding is critical

use of oxen helps to reduce effort of weeding

line planting makes weeding easier

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many ox-drawn or manual implements exist which would lighten the work load if they were accessible (often would require rural credit and better advertising/extension from research stations) - often not enough profit in simple farm implements

Note : -

some "weeds" are an important emergency food supply – they are left on purpose not because the farmers are ignorant – other weeds may have a cash value

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Weeds may have soil conservation benefits, even on low slopes

clean weeding can increase soil erosion on slopes over 2%

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Choice of crop & variety

Need well adapted varieties.

Various strategies are adopted to make best use of moisture, e.g.:

short duration,

drought resistance,

lower Leaf Area Index (so lower evaporation demand),

higher Leaf Area Index (so lower splash erosion),

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rapid growth rate (establish protective ground cover quickly),

smaller leaves better (drips smaller and breaks up rain more effectively),

short crops better than taller crops because of more dispersed stem flow.

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Indian Cultivar Database

participatory varietal development

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Search for types which are morphologically and physiologically adapted to the conditions

Mesophytes

moist conditions required

Xerophytes

withstand high soil water potentials by: large root system waxy or very small leaves other physiological modifications

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Pseudo-xerophytes

avoid drought (opportunistic) germinate after rain very short growing season complete cycle before stress experienced

Halophytes

salt resistant

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Phreatophytes

water-loving plants

water from WT may occur even in arid regions - or water-logging during rainy season

Lomas

water from fog or mist (e.g. Namibia, Peru, Chile, Mexico)

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Contour strip cropping

Sedimentation by vegetated strips

Critical factors are density, shape, resilience of grass.

Friction of vegetation causes water to slow down - depth increases.

Detachment decreases because of increase in water depth

Sediment transport capacity decreases because of roughness.

Foreslope becomes steeper than ground slope.

Potential increase in velocity tends to be offset by roughness of grass stems.

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When fore-slope coincides with edge of barrier, velocity increases due to decrease in roughness,

water is sediment free so may have considerable erosion potential

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Crop 1

Crop 2

Crop 1

Crop 2

etc.

Slope

Design of strip cropping systems

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Strips should be of equal width

May be good interim measure if farmer has no time for more permanent measures or is doubtful about their efficacy

Temporary grass + small grain strips reduced erosion by half at one site in E. Africa

Another possibility is to have alternate crops e.g. legume / grain, instead of crop and grass

Crop 1 is sometimes bare soil (see water harvesting section)

There are logistical problems with mechanisation & grazing. Difficult to negotiate.

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Contour strip-cropping designs for five-year crop rotation

Row crop 1Row crop 2Row crop 3Small grainHay

Waterway to drain surplus flow

strips followcontours only approx

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buffer stripsof grass

include rocky areas in buffer strip

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840.01

0.1

1

0 0.5 1 1.5 2 2.5

Strip width (m)

Ra

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of

ou

tflo

w t

o i

nfl

ow

ing

se

dim

en

t o

r ru

no

ff

Soil loss

Runoff

Relationship of grass strip width to ratio of outflowing and inflowing sediment or runoff

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Contour hedgerows – form of strip cropping

Function & benefits litter / roots / undergrowth - slow down water (so

reduces erosion), & encourages deposition leaf manure or cuttings for mulching wind break (but contours may not be at right angles

to wind) cash income - timber / fodder fodder can be N fixing (though benefits generally

disappointing) increase of infiltration / reduced runoff due to better

soil structure may reduce erosion by factor of 10 depending on

spacing, location

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Why contours? danger of low spots concentrating ponded water NOTE - problem of steep forward slopes

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Negative indications

• hedgerow - crop competition for water & nutrients - crop yield reductions commonly observed

• cost of establishment & maintenance• space occupied if land shortage• rapid loss due to leaching of nutrients / bases gained• farmer reluctance especially small farmers• grazing by cattle• psillid attacks of Leucaena spp. increasing problem

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Where they may be considered

• steep land (up to 20% ?)

• high erosion rates

• high human population

• land productivity poor to moderate & declining but not suitable for infertile soils

• maize dominated systems (or upland rice?)

• bimodal rainfall (> 1000 mm pa)

• not suitable for areas prone to severe drought during growing season

• pH > 5.5

• scarcity of trees

• secure land tenure

• widespread ownership but confinement of livestock

• primary dependence on agriculture

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Handout - table of species used and some observations in literature

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Urban waste as soil conditioner

Urban waste if properly separated and treated can be added to soil to improve chemical and physical properties.

Sewage and “night soil” - treated or untreated - is used for irrigation in many countries - Ghana experience

Need more research on how to (minimally) treat and manage waste for agricultural production - especially sewage

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Possible competing uses

Household waste

• recycling of solid waste

• fuel - after drying and compaction;

• decomposed waste for mushroom, yeast, algae growing;Food waste

• animal feed - only if discarded food is collected (especially in urban environments);

Night soil and sewage

• aquaculture (faeces encourages growth of algae, rotifers, crustaceans)

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Factors affecting the use of waste in agriculture:

• type of agriculture (farming system, rural livelihoods, crops, livestock);

• economics:• markets (for farm produce and for waste);• alternative uses may be more profitable• affordability;• transport costs;• separation and collection costs;• labour availability and costs;• availability and cost of alternative soil

ameliorants;

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knowledge, perceptions, preferences, social and cultural factors, aesthetics, odour;

land tenure (farmers reluctant to invest in insecure holdings) and land availability;

geography - distances involved; economics nitrogen immobilisation due to high C:N ratios; variable quality (spatially and temporally); phyto-toxicity (ammonia "burning", salt, phenolics,

low molecular weight organic acids); health safety, environmental perceptions of risk; institutional support or lack of it

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Socio-economic and institutional factors - Hubli/Dharwad

• farmers quite experienced in using composts including MSW;

• farmers prefer organic fertilisers to inorganic sources of nutrients;

• wealthy farmers have been the main purchasers of compost;

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• farmers constraints include:• transport - especially resource-poor farmers do

not have access to compost, mainly because of the large transport costs;

• increasing labour shortages / costs (due to competition) at dump sites (to dig pits) and for farmers (to sort the waste and empty pits);

• declining quality (especially increasing amounts of plastic (farmers without tractors are increasingly reluctant to hire then for low quality material).

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• composts are in increasingly short supply some farmers now till the soil earlier to adapt to changes in availability of composts;

• the proposed vermi-composting of MSW by commercial sector (in Hubli-Dhawad) will be even less accessible to resource-poor and marginal farmers;

• use of animal manure for composting is becoming more problematic since:• there is continuing competition for its use as a

fuel as well as compost component;• there is a declining availability of animal

manure as a result of mechanisation;• there is proposed legislation that would evict

cattle from cities of over 500,000 inhabitants.

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source separation is an important bottleneck but it is difficult to achieve significant committment to source separation to make an impact (as many people believe that waste management is the role of the municipal authorities);

there is a range of different sources and used of waste but there is a need to be better understand the interactions between these;

the municipality has an inadequate waste collection system;

the dump sites are not managed / sited in an environmentally sensitive way;

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subsidies are suggested to reduce the cost of processed waste;

farmers should be allowed access to MSW tips in addition to the private sector;

the private sector and NGOs should be persuaded to become involved in the separation, processing and distribution of waste products and that there is a range of products sold at different prices;

different methods of composting need to be explored (turning composts in pits is difficult);

the health and management aspects of incorporation of night soil needs further exploration

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Gender issues women were increasingly entering paid

employment including farm labour; source separation within households and waste

picking generally is done by women (and children);

changes in the market for waste will affect women's livelihoods.

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ProcessingComposting MSW:• increases soil porosity and this infiltration;• increases enzyme activity;• increases yield (maize cited);• decreases leaching of nitrogen;• can be improved by adding rock phosphate, urea,

or inoculating with Azobacter chroococcum or Aspergillus awamori;

• sanitises waste (kills off almost all pathogens if the temperatures of the compost is high enough or the waste is stored for periods of about a year ) [in the Hubli-Dhawad trials, 90 days seemed to be a sufficient length of time for the composting to take place but there is a need to determine the optimum time and conditions (from composting and health viewpoints);

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• reduces waste volume;• reduces phytotoxic properties (e.g. high C:N ratio).• possible combinations:

• sawdust + nightsoil;• MSW + nightsoil;• sawdust + poultry manure

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MSW in Hubli-Dhawad consisted of: 35% compostable waste; 35 to 40% of plastics, glass,

rubber; 15 to 20% of building debris; 5% of metal; 5 to 10% of woody biomass.

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Soil fertility value of waste: primary nutrients (quote MSW from India as

0.5% N, 0.3% P, 0.3% K); changes in physical properties of soil due to

organic matter which : increases rainfall infiltration (and so

decreases runoff and erosion); increases water holding capacity and

aeration, improves structure (and so decreases

susceptibility to soil crusting); use as surface mulch to depress weed growth

and conserve soil moisture; can act as delivery agent for microbial control of

pests (e.g. - citrus in California);

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inhibiting effect on soil borne plant pathogens;

suppression of nematode populations; wood ash can be used for Ca deficiency

(groundnuts at flowering cited) or K deficiency (tomatoes at flowering cited);

rice husks used for silicon deficiency. modalities for use, rates, combinations are

under-researched.

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Trials to investigate potential use of waste as a soil conditioner around Hubli-Dhawad

The trialsThe trial were conducted on 10 farmers fields in 2 villages. (The farmers selected do not appear to have been particularly poor)

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The treatments used for the trials were: sorted MSW; sorted MSW + 25% Distillers Sludge (DS); sorted MSW + 50% DS; sorted MSW + 75% DS; sorted MSW + vermicomposting (V); sorted MSW + vermicomposting (V) + 50% DS; sorted MSW + Azospirillium bacteria + rock

phosphate; sorted MSW + 5% cattle manure; sorted MSW + 25% DS + 5% FYM; sorted MSW + 25% night soil (NS).

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In the trials with distillers sludge and night soil, 1 kg / ton of each of the following bacteria were added :

Bacillus polymyxa (phosphorous solubilising); Azospirillum spp. (nitrogen fixing).

A summary of the chemical analyses of the various treatments compared to pit compost (FYM) is given in following table

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Summary

• No treatment stands out in terms of nutrient levels and their performance from a nutrient point of view would depend on the soil and crop.

• Generally, the additions of night soil or brewers sludge improved the MSW as did vermicomposting.

• Nitrogen and Potassium were both lower for all the treatments than for FYM and only MSW + V and MSW + NS had slightly higher P values.

• EC indicates that all the treatments are marginally saline. There may be some potential for salt build up, especially in the black soils which have impeded drainage.

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• Levels of Mg, Cu and Mn are all much higher in the treatments than the levels in FYM but are not thought to be a problem. These may be beneficial though we know little about the existing micro-nutrient status of the soils or the uptake by the crops.

• More research on heavy metal aspects of MSW based products is required. In particular metals such as mercury, lead, cadmium and chromium need to be assessed.

• Dioxin levels also need to be determined. • The constitution varies by season.

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Comparison of treatmentsOverall performance of the different treatments on four different crops in 10 villages (UWB-60, p. 35) were (in order of performance) :

sorted MSW + night soil; sorted MSW + vermicomposting; farmers practice; sorted MSW alone; sorted MSW + distillers sludge.

The trial only ran for one season and it was suspected that benefits were not necessarily obvious in the first season. Longer term trials would be needed to address this question.

Night soil or vermi-composting seem to be the most advantageous treatments and this was supported by analyses of nutrient uptake by crops.

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Use of sewage around Hubli-Dhawad no treatment of sewage around Hubli-Dhawad, even

though it is estimated that 60,000,000 litres of sewage per day are produced

some liquid presumably drains to the water table, but much of the solid and liquid sewage finds its way into the surrounding water courses.

sewage contaminated stream water (around Hubli-Dhawad) does not suffer from heavy metal contamination due to the absence of heavy industry in the area

total suspended solids (110 mg l-1) and dissolved solids (780 mg l-1) were both high - latter could affect salt sensitive crops

nitrogen concentration was around 12 ppm which partly explains why the yields of stream irrigated crops are (anecdotally) 25 to 30% higher than those irrigated from boreholes.

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Major drawbacks of the use of sewage contaminated water seems to be:

increased levels of weeds and insect pests on crops (which, because of the high value of the crop, encourages farmers to use organo-phosphates, often with no protective clothing);

incidence of conjunctivitis and dermatological conditions among farmers.

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Advantages: producing vegetables for sale during the dry

season means that farmers can sell for 3 to 5 times the kharif season prices

pumping from a water course is cheaper than from a borehole, it is more accessible to farmers with fewer financial resources.

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Research needsThis topic needs further research, especially:

quality and quantity of sewage contaminated water available;

groundwater monitoring for contamination (wells and boreholes);

soil nutrition and toxicity aspects; IPM methods for managing the relatively high

levels of pests; to clarify the human health hazards.