Present - Danish Water Forum

Present - Danish Water Forum

Present - Danish Water Forum


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Low-cost soil- & water-conservation<br />

with many early benefits<br />

(’Climate change increases incidents of extreme rainfall’ in on-line programme, oral and poster<br />

presentation)<br />

By Torsten Mandal,<br />

agronomist, independent consultant, external PhD student.<br />

Acknowledgement:<br />

-N E Nielsen, Lab. Soil Fertility & Plant Nutrition, Inst. Agric. Sci.,Faculty Life Science, Univ.<br />

Copenhagen<br />

-D Nyamai, Kenya Forestry Research Inst.<br />

-Danida and other sponsors.<br />

Contact:<br />

TorstenMandal@gmail.com<br />

Google: “Torsten Mandal” IOP or XPS for articles<br />

A) OBJECTIVE: Briefly, more sustainable, cost-effective methods are increasingly<br />

needed for reducing sudden surface water-runoff and drought damages while improving<br />

food- and feed-security. Nitrogen-fixing multipurpose trees related to beans (legumes) are<br />

needed in large numbers; but new solutions to establishment and management problems<br />

were badly needed. Recycling of ash from kitchen-firewood to nitrogen fixing trees was<br />

one of the solutions.<br />

Global warming increased extreme rainfall events (and drought) even more than<br />

previously thought and modelled (Allan and Soden 2008, Sugiyama et al. 2010). Rapid,<br />

superficial, water-runoff leads to erosion, landslides, sedimentation, water pollution, formation<br />

of mosquito-pits, and lack of drinkable water, etc. Preventing runoff is more cost-effective,<br />

than treating damages but is often neglected by urban-based decision-makers.<br />

Sustainable adoption of soil and water conservation requires early benefits to landusers<br />

as well as low establishment and maintenance costs. The major cost for a popular<br />

method, e.g. in central Kenya, Rwanda and SW Uganda, is watered, transplanted, nitrogenfixing<br />

tree seedlings, particularly of calliandra (Calliandra calothyrsus). More reliable direct<br />

seeding methods were needed giving early benefits.<br />


FIGURE 1. Calliandra hedge direct seeded with improved methods by small scale farmer.<br />

Such tree species can protect the soil surface by providing low cover, stabilize soil<br />

aggregates and terraces, improve water infiltration, add nitrogen to fodder grass lines, and<br />

provide good firewood and dry-season feed-supplement. The direct soil conservation effects of<br />

such tree-legume hedges are important but with much variation and much room for<br />

improvement (e.g. Nkonya 2008, Young 1997). Improved low-input establishment of fodder<br />

hedges by direct seeding as suggested by Mandal and Nielsen (2004) is also needed to prevent<br />

overgrazing causing erosion and run-off (Thomsen et al. 2007).<br />

Dry periods and heat are major challenges, for both transplanted and direct seeded trees, and<br />

require enough coarse roots (>2mm) that can transport water up from deep moist soil through<br />

dry soil (e.g. pers. obs.). Effects of phosphorus (P) application on root growth needed studies,<br />

and so did wood-ash as a source of P. To prevent landslides, numerous hedges with much<br />

coarse roots and short light tops are needed. Accordingly, new options for direct field<br />

seeding of calliandra were studied to ensure a rapid, early growth in poor soils, despite<br />

unpredictable climate. So are more appropriate options for managing contour hedges for<br />

soil and water conservation compatible with producing firewood, feed and crops (Mandal<br />

and Nielsen 2002; Mandal and Nielsen 2004; Mandal (unpublished).<br />

B) METHODS: The data were obtained with calliandra from various replicated researchmanaged<br />

trials in farmers’ fields at the humid and mainly subhumid zones, having two annual<br />


ainy seasons, in Western Kenya near Maseno research centre near the equator at about 1400 m<br />

altitude. The wood ash experiment was with only 1 m distance between hedges (as used with<br />

improved fallows) and 0.1 m within row. The wood ash (1.3% phosphorus =P) was mixed<br />

well into 20 cm wide bands and 10 cm deep (normal hoeing) placed 5-15 cm below seeds.<br />

FIGURE 2.<br />

FIGURE 2. Calliandra seeds were scratched to ensure water uptake and avoiding risky<br />

hot water pre-treatments and soil enriched with kitchen wood ash and nitrogen fixing<br />

bacteria.<br />

Farmer participation and laboratory studies were also used to develop and check the solutions.<br />

Hedge-management and soil-and-water-conservation effects were mainly studied by<br />

observation studies. See Mandal and Nielsen (2002, 2004) and below for details.<br />

C) RESULTS:<br />

Low-input solutions were comparable to the best conventional solutions, and key results<br />

were at least twice as good as with no treatment control, and were statistically significantly<br />

better. Improvements included:<br />

1) After only 14 days, 87% field germination was achieved by scratching the waterproof<br />

seed-surface with a sandal against a rough concrete floor (no watering, Mandal and Nielsen<br />

2004). Without effective seed pretreatment, it took 7 weeks to get 50% germination, often too<br />

late to survive weeds, the dry season starting 4 month later, and cultivation. Soaking mature,<br />

dry, undamaged calliandra or Sesbania sesban seeds in unheated water 3 days, as recently<br />

recommended to farmers, did not induce any visible water uptake in any of 20 seeds because<br />

they were dry, mature and undamaged (unpublished), No Leucaena leucocephala seeds took up<br />

water after 35 days in unheated water (e.g. Mandal 1994).<br />


Field germination, %<br />

2) Germination of the small weed seeds during a dry spell was significantly decreased to less<br />

than the half by leaving the 5-cm soil-surface loose above the bigger calliandra seeds so water<br />

could not be sucked up to the weeds by soil (Mandal and Nielsen 2002). Most farmers were<br />

not aware of the fact that firming seed below desired seeds (or seedlings) increased tolerance to<br />

drought.<br />

3) Good root-nodulation (by transferring 10 g colonised soil, or a soil-incubated nodule m -1<br />

hedge (7 days locally and then crushed) for atmospheric nitrogen fixation when needed (Mandal<br />

and Nielsen 2004).<br />

4) Fair germination of calliandra in continuously continuous direct sun was achieved by<br />

removal of hot soil 5 to 7<br />

days after seeding from a 70<br />

ridge above germinating<br />

seeds else germination<br />

failed,<br />

60<br />

FIGURE 3:<br />

Hot sun all<br />

day<br />

50<br />

Light shade<br />

FIGURE 3.<br />

Germination during dry<br />

sunny period of<br />

Calliandra calothyrsus.<br />

40<br />

30<br />

20<br />

5) About 2 to 3.5 times<br />

higher dry matter<br />

production was obtained at<br />

13 to 30 weeks after direct<br />

10<br />

seeding (by mixing about<br />

1% kitchen wood ash well<br />

into the nitrogen- and 0<br />

phosphorus-deficient soil at<br />

Controle Removed<br />

20 cm width by 10 cm<br />

Removal of hot soil surface<br />

depth (from 5 to 15 cm<br />

below the seed to prevent<br />

scorching).<br />

Low phosphorus (=P) mobility and plant uptake are big problems for nitrogen fixing plants<br />

in tropical soils, particularly for young plants and during droughts. Moderate ash dose<br />

significantly increased P-uptake as much as economically optimal doses of P fertilizer 13<br />

weeks after direct seeding of calliandra tree-legumes on N and P deficient soil. FIGURE 4:<br />


P above ground, kg/ha<br />

1<br />

0.8<br />

Wood-ash<br />

TSP<br />

0.6<br />

0.4<br />

0.2<br />

0<br />

0 60 120 180<br />

kg phoshorus (P) / hectare<br />

FIGURE 4. Phosphorus uptake 13 weeks after seeding calliandra supplied with kitchen<br />

wood ash or triple super phosphate.<br />

Aboveground biomass was also strongly increased by moderate wood ash doses even 30<br />

weeks after direct seeding (FIGURE 5 a, below).<br />

The best dose for early root and top growth after only (13 to 25 weeks after direct seeding,<br />

150 g/m ash, 20 kg P/ha), also increased 30 weeks root growth including coarse roots in the<br />

enriched zone strongly, but not high ash doses (FIGURE 6 b). Other root-results varied much.<br />

Fresh ash is very alkaline (pH 11 to 13) and with high content of soluble salts. Deep root<br />

growth in acid subsoil can be improved by liming (e.g. with kitchen wood ash) and by better top<br />

growth.<br />

Accordingly, leaflet-pairs for the 20-dose were at least as open as for controls early in the<br />

dry season indicating good water uptake (FIGURE 6 c):<br />


Leaves+stem dry<br />

weight, kg/ha<br />

Coarse root d.w.,<br />

enriched zone, kg/ha<br />

Leaflet opening,<br />

degree<br />

10000<br />

9000<br />

8000<br />

7000<br />

6000<br />

5000<br />

4000<br />

3000<br />

2000<br />

1500<br />

a<br />

0 20 40 60 80 100 120 140 160 180<br />

b<br />

kg phosphorus (P) /hectare<br />

1300<br />

1100<br />

900<br />

700<br />

500<br />

c<br />

90<br />

wood-ash<br />

TSP<br />

80<br />

70<br />

0 60 120 180<br />

kg P / hectare<br />

FIGURE 5 a b c. Effects of wood ash or triple super phosphate.<br />

Accordingly, at the start of the dry season, 30 weeks after direct seeding (not before), rootnodulation<br />

was several times higher when 20 to 60 kg P hectare -1 was applied as wood ash<br />

rather than TSP. It also indicates good potential for nitrogen fixation and growth at dry times.<br />

More drought tolerant and nutrient demanding species can also be chosen like suitable<br />

proveniences of Leucaena trichandra or Sesbania species.<br />


Weeds, g<br />

6) Competition for water etc. with faster growing weeds is a problem with standard methods.<br />

In the mentioned ash experiment only high P-fertilizer doses to calliandra increased the critical<br />

early weed and calliandra growth much, increased shade on the hot soil surface can have<br />

contributed, FIGURE 6:<br />

45<br />

FIGURE<br />

6. Early weed<br />

growth with wood<br />

ash or rapidly<br />

soluble phosphate<br />

near hedge.<br />

40<br />

35<br />

30<br />

25<br />

wood-ash<br />

TSP<br />

In a separate<br />

experiment, early<br />

weed growth was<br />

not increased by<br />

wood-ash. In<br />

contrast, it was<br />

increased much by<br />

rapidly water<br />

soluble P-fertilizer<br />

(TSP), particularly<br />

when combined<br />

20<br />

15<br />

10<br />

5<br />

0<br />

0 20 40 60 80 100 120 140 160 180<br />

kg phoshorus (P) / hectare (ha)<br />

with N-fertilizer (Mandal and Nielsen 2002). Local cow-manure also increased weed growth<br />

much in another (unpublished). Slow weed growth reduce risk of damage to hedges by<br />

weeding by workers close to seedlings and to soil/water-conservation effects.<br />

Further, maintenance of water conservation structures was much easier under the<br />

young hedges growing well. In farmer’s fields, terrace formation was by sedimentation was<br />

impressive when cultivation was not too close, and distance between trees 10 cm rather than<br />

the usual 30 cm. Stable edges of 30 cm could be seen about five years after establishment in a<br />

field with slight slope. This confirms the need of effective direct seeding methods. Farmers’<br />

often used new hedge management methods when introduced to them.<br />

Formation of wood and seeds as well as preservation of feed, green manure and near-ground<br />

protective soil cover is a challenge when only cutting is advised. In observation studies,<br />

farmers found the following three new options we developed useful to delay cutting of stems<br />

grown in rainy seasons between crops:<br />

A) Partial breaking over a knee of 0.5 to 3 cm thick stems,<br />


B) Stripping off composite leaves with a forked branch sparring the tip, stem and the cover<br />

near the ground, and/or<br />

C) Bending and twisting stems together.<br />

FIGURE 7.<br />

FIGURE 7. Young calliandra stem stripped with forked branch.<br />


FIGURE 8.a. Lowest calliandra branch stripped with forked branch.<br />

These methods prevent much shading in cropping seasons, make protecting ground-near soilcover<br />

possible at the start of the rainy seasons, and allow time to develop wood that is more<br />

useful, seeds, dry season feed and nectar.<br />


Direct field seeding can be done on flat ridges, and short water conservation furrows can be<br />

constructed above the contour line during establishment, below them later. Soil around mature<br />

stems was tolerated, and it can increase water conservation and tolerance to fire. Weeding<br />

under hedges can be minimized if kitchen wood ash is used instead of fertilizer or manure.<br />

Finally, the only 10-cm in-line distance between shrubs possible can be used to trap litter and<br />

increase water infiltration.<br />

Direct seeded calliandra can also grow on degraded grassland, or on stony hills where it can<br />

hold back run-off water, soil, organic matter and seeds from other species so some of them grow<br />

spontaneously, e.g. Senna spectabilis providing termite resistant wood needed for crop stores<br />

improving ability to cope with unpredictable climate (FIGUR 9).<br />

FIGURE 9. Stony hill-top re-vegetated by useful direct seeded tree-legumes.<br />

D) CONCLUSIONS: Improved low-input methods can contribute to better soil and water<br />

conservation, increase wood growth, and supply soil with nitrogen-rich organic matter and<br />

provide drought tolerant feed supplement. The methods are attractive, reliable and<br />

sustainable for e.g. small-scale farmers in an unpredictable tropical climate. This can reduce<br />

many important climate-related problems (heat, drought, flooding, erosion and CO 2 -emission).<br />


E) ACKNOWLEDGEMENT: Danida for research grant, various funds for support, late<br />

Professor N E Nielsen, Faculty of Life Science, University of Copenhagen and Dr. D Nyamai<br />

(then Head of Agroforestry Division Kenya Forestry Research Inst., now at World Agroforestry<br />

Centre) for supervision. <strong>Present</strong> PhD supervisors Professor J K Schjørring and Dr. A de<br />

Neergaard. The collaboration with CARE Denmark+Rwanda, ICRAF, and Vi Agroforestry<br />

(Tanzania and Kenya as consultant), at various stages between 1990 to 2009 is also appreciated.<br />


Allan R P and Soden B J 2008: Atmospheric warming and the amplification of precipitation<br />

extremes. Science 321, 1481 – 1484.<br />

Thomsen N, Nielsen M O, Hansen J, Henriksen J, Madsen J, Jensen H A, Mandal T, 2007.<br />

Give a goat - assessment project 2007 <strong>Danish</strong> Church Aid, Copenhagen, Denmark.<br />

Mandal T 1994 Pre-treatment of hard coated seeds of leguminous shrubs. In: The 4 th<br />

International Symposium. Windbreaks and Agroforestry. July 26-30 1993,<br />

Hedeselskabet, Viborg, Denmark, pp. 233-236.<br />

Mandal T and Nielsen NE 2002: Direct seeding of multipurpose tree-legume hedges using an<br />

improved method. In: Ramalho-Filho A et al (eds) Proceedings of the Third<br />

International Conference on Land Degradation and Meeting of the IUSS<br />

Subcommission C - Soil and <strong>Water</strong> Conservation. Rio de Janeiro, September 17-21,<br />

2001. Rio de Janeiro, Embrapa Solos.<br />

Mandal T and Nielsen N E 2004 An improved low-input method for establishing calliandra<br />

hedgerows on small-scale farms in western Kenya. Agroforestry Systems 60: 227-231.<br />

Nkonya E, Gicheru P, Woelcke J, Okoba B, Kilambya D, Gachimbi L N 2008: On-Site and offsite<br />

long-term economic impacts of soil fertility management practices. The case of<br />

maize-based cropping systems in Kenya. IFPRI Discussion Paper 00778. Environment<br />

and Production Technology Division. Int. Food Policy Res. Inst.<br />

www.ifpri.org/pubs/dp/ifpridp00778.pdf.<br />

Sugiyama M Shiogama H Emori S 2010 Precipitation extreme changes exceeding moisture<br />

content increases in MIROC and IPCC climate models Proceedings of the National<br />

Academy of Science of the United States of America 107, 571-575.<br />

www.pnas.org/cgi/doi/10.1073/pnas.0903186107.<br />

Thomsen N, Nielsen M O, Hansen J, Henriksen J, Madsen J, Jensen H A, Mandal T, 2007.<br />

Give a goat - assessment project 2007 <strong>Danish</strong> Church Aid, Copenhagen, Denmark. Free<br />

PDF.<br />

Young A 1997: Agroforestry for Soil Management 2 nd ed. ICRAF and CAB Int. 320 pp.<br />


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