African Journals Online
Transactions of the Zimbabwe Scientific Association

Volume 72 (Supplement) 1998

Environmental Adaptation and Performance of Various Agroforestry Tree Species in Zimbabwe
BEN. H. DZOWELA

Project Leader, ICRAF-Zimbabwe Agroforestry Project, P O Box CY 594, Causeway, Harare, Zimbabwe

Abstract
The experience of the ICRAF-Agroforestry project is drawn in this paper to identify adapted agroforestry trees for Zimbabwe conditions. From the experience with trees at Domboshawa and Makoholi, certain tree species have performed well in target technologies. A wide range of Leucaena species and provenances show potential for fodder bank technologies. These can now be considered as alternative species to the psyllid-prone L. leucocephala. Other non-Leucaena species include Acacia angustissima and Calliandra calothyrsus. Emphasis is placed on targeting these agroforestry tree species for specific functions and services.

Performance of Some Multi-purpose Tree Species: the Forestry Commission Experience.
ABISAI MUSHAKA and DZIDZAI MARUZANE

Forestry Research Centre, Forestry Commission, P O Box HG 139, Highlands, Harare
e-mail: [email protected]

Abstract
Rural afforestation in Zimbabwe has been heavily reliant on the genus Eucalyptus. Limited success has been achieved with these species in semi-arid areas. To broaden the species range and provide a wider product range, the Forestry Commission of Zimbabwe has been conducting on-station screening of African and Australian acacias. Of the African acacias, Faidherbia albida and Acacia tortilis exhibited high survival rates within the first year. Of the Australian acacias, Acacia auriculiformis succumbed to termite attacks except at Chesa and Acacia holosericea and Acacia colei appeared to be less susceptible to termite attack. Eucalyptus camaldulensis, Eucalyptus leptophleba and Eucalyptus tereticornis had better survival percentages than the acacia species tested. There are some indications that some acacia species, given more testing, can be selected for afforestation purposes in areas where eucalypts have been traditionally used. In Shurugwi, an evaluation of the performance of some multipurpose tree species planted out by farmers was carried out at eight years. The mortality of the tree species on-farm was variable, ranging from 39 to 64% in 1991 and 2 to 54% in 1996. Leucaena leucocephala, A. holosericea, Melia azedarach and Senna atomaria had the greatest growth and biomass production. Farmers preferred L. leucocephala and Casuarina cunninghamiana, which was correlated to their ability to produce useful poles. It is recommended that research that develops cost-effective strategies to improve survival levels of planted trees should be supported and alternative pole producing species should be made available to small holder farmers.

Annual Legumes for Improving Soil Fertility in the Smallholder Maize-based Systems of Zimbabwe
DANISILE HIKWA¹ & STEPHEN R. WADDINGTON²

^1. Agronomy Institute, DR & SS, P O Box CY 550, Causeway, Harare.
^2. Soil Fert Net-CIMMYT, P O Box MP163, Mount Pleasant, Harare. e-mail: [email protected]

Abstract
Annual legumes are widely grown by smallholder farmers in Zimbabwe. In addition to providing food, these crops are widely recognised to help maintain soil fertility. In this review we highlight their soil fertility benefits and shortcomings and suggest areas for future work. Most of our knowledge about the soil fertility benefits from annual legumes has come from research stations where they have been demonstrated to input large amounts of N and organic matter. But we still know surprisingly little about the magnitude and dependability of those gains on smallholder farms in Zimbabwe where acidic sandy soils, rainfall extremes and pests often place severe limits on legume growth. Recent work suggests that benefits under those conditions with traditional annual legumes such as groundnuts are much smaller and take longer to achieve than on research stations. We need to screen new legumes for local adaptation to see if there are new species or accessions that do better on smallholder farms. Some green manures, especially velvet beans, have given a reasonable biomass on extremely nutrient depleted and fairly acidic soils, and have potential to help rehabilitate degraded fields when coupled with lime and P. Green manuring will be difficult for smallholders to adopt unless large benefits can be obtained quickly. More work with velvet beans is required on farms to establish the size and speed of yield gains for following maize crops. Also, more participatory work amongst farmers is needed to integrate green manures into existing farming systems. Smallholder farmers already rotate grain legumes with maize. In many cases the rotation does help maintain productivity and soil fertility although at levels much reduced from those found on station. Further long-term on-farm work with the farmers being closely involved is needed to measure benefits from the rotations, and to examine the technology and management options to help farmers grow better crops of existing and new (such as promiscuous soybeans) grain legumes both for their direct benefit as food and the subsequent benefit to succeeding cereal crops. These options would include use of fresh seed, lime and perhaps P. The intercropping of grain legumes with maize can often raise the productivity of land, except in dry areas. Although farmers are rarely going to intercrop annual legumes primarily to improve soil fertility, spin-off benefits on soil fertility may still be worthwhile and have recently been achieved on station in Zimbabwe. These have yet to be demonstrated and quantified on smallholder fields through longer-term trials. In conclusion, although benefits will often not be large, annual legumes can help to maintain soil fertility on smallholder farms in Zimbabwe. The farmers will need more help to access seed of a range of annual legumes that they can integrate into their farming system. A bigger effort by research, extension and seed houses to produce and distribute seed at prices affordable to smallholder farmers is necessary, along with more appropriate guidance on crop management.

Crop-Livestock Interactions: Considerations of Direct and Indirect Utilization of MPTS and/or Herbaceous Biomass in Soil Fertility Management
LINDELA R. NDLOVU¹

Department of Animal Science, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare e-mail: [email protected]

Abstract
In smallholder farming systems, crops and livestock complement and compete with each other in terms of natural resource use. Supply of manure to the cropping system and use of resultant crop residues are an example of this interaction. Tree forages are valuable sources of nutrients for livestock and they are also important in soil amendment. The dilemma is whether to apply the tree forages directly to the soil or to pass them through animals ( as feed) and apply the manure to the soil. Legume tree foliage tends to contain tannins that regulate nutrient release and affect distribution of nitrogen (N) in animal excreta. Most urine N is lost through volatilisation whilst N excreted in faeces could be mobilised for plant uptake. Manure has been shown to be higher in content of phosphorus (P), lignin and nitrogen and to result in faster mineralisation of N and P than leaves. However this is based on a limited number of studies and there is a need for well-designed studies that compare manure from animals fed specified tree forages of the same plants incorporated directly into the soil as part of the same experiment.

Soil Fertility Replenishment through Agroforestry Systems in Two Contrasting Agroecological Zones of Zimbabwe
PARAMU L. MAFONGOYA¹ and BEN H. DZOWELA²

¹Zambia-ICRAF Agroforestry Project, P.O. Box 510089, Chipata, Zambia
²Zimbabwe-ICRAF Agroforestry Project, P.O. Box CY 594, Causeway, Harare, Zimbabwe
e-mail: [email protected]

Abstract
The main limiting nutrient in most communal areas of Zimbabwe is nitrogen (N). There is also deterioration of soil physical properties without continual addition of organic matter to the soil. Soil fertility replenishment through agroforestry technologies such as biomass transfer and improved fallows are discussed in terms of their potential to alleviate N limitations to increase maize yield. Various management practices to enhance the nutrient use efficiency on these systems are discussed. Areas of future resources are suggested.

Potential Role of Agroforestry in Maintaining Soil Fertility on Communal Dambos of Matopo: Towards a Holistic Approach to Dambo Management.
DANIEL SITHOLE

Research Development and Consultancy Division, ENDA-Zimbabwe

1 Waterfield Road Mt. Pleasant, Harare, Zimbabwe. e-mail: [email protected]

Abstract
The paper presents some of the findings of a study on communally managed dambos of Matopo. Despite legislation curtailing their use, they are being used for grazing, and crop and vegetable production. The soils in the cultivated dambos suffer from major phosphorus and sulphur deficiencies and have low nitrogen and organic matter content. Organic fertilizers play a significant role in maintaining soil fertility on these dambos but the problems of deforestation and land shortage are adversely affecting this management strategy. Agroforestry in the cultivated areas of the dambos and over the whole catchment area is seen as a practical solution as it has multiple benefits for the communal farmers. Live fences around fields provide protection from livestock, help to stabilise the soil and aid in nutrient cycling by providing prunings as a source of organic matter. They also reduce pressure on forests by replacing their role as sources of fencing material. The potential of relay cropping with Sesbania is also explored as it has multiple benefits that include improving soil fertility, and the conservation of soil and moisture, and the supply of fuel wood.

Changing C and N Levels of Miombo Woodland Litter
FLORENCE MTAMBANENGWE

Department of Biological Sciences, University of Zimbabwe,P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe e-mail: [email protected]

Abstract
Litterfall was collected fortnightly from four-25 m² cleared miombo woodland plots for five years. The litter was fractionated and compared for quantity, monthly distribution and concentrations of total C and N. Annual litterfall, starting at the beginning of the dry season (May) to the end of the rainy season (April), ranged from 283.3 to 507.8 g m^-2 year^-1. A peak of litterfall occurred in all the five years during the May to September period. Although the proportion varied from year to year, leaflets litter were always the largest component of the annual litter fall ranging from about 34-44% of total litterfall. This represented an annual nutrient pool of between 546-1043 kg C ha^-1 and between 17-31 kg N ha^-1. Although C contents in each litter fraction did not differ significantly during the 12-month sampling period, total N concentrations differed greatly during the same periods (p < 0.05). While N concentrations showed considerable declines from July to October in most of the litter fractions, seed litter showed a significant N increase. C:N ratios were lowest in litter collected during the mid-rainy season (December to March), 22 and highest in September, 43 implying that mid-rainy season miombo litter may have the potential of releasing N to growing plants. These results show that there may be need for more detailed studies relating organic materials used in soil fertility improvements to synchronize with plant demand.

The Value of Trees in Low Input Agriculture Systems in Zimbabwe
PETROS NYATHI

Department of Research and Specialist Services, P.O. Box CY 594,Causeway, Zimbabwe e-mail: [email protected]

Abstract
The objectives of this study, done at the Makaholi Experiment Station, Zimbabwe, were to evaluate the effects of organic inputs, applied at 5t ha^-1, in various combinations with inorganic fertiliser on the growth and yield of maize over three seasons, beginning in 1990/91. The inputs included manure, leaf litter from Brachystegia spiciformis (miombo), senesced leaves of Lucaena leucocephala, and Compound D fertiliser (8N-14P-7K). Inorganic fertiliser in combination with miombo litter and/or manure gave a higher biomass and yield of maize in the third season compared to organic litter alone. A synergism seemed only to exist when inorganic fertiliser was included in the inputs. The positive response of maize to the application of litter suggests that trees contribute to crop production via the transfer of litter. The loss of soil fertility and the subsequent decline in crop yields supports these results and demonstrates the value of trees in providing nutrients to crops. Smallholder farmers in Masvingo collect woodland litter and termitaria soil in an effort to reverse the decline in the fertility of sandy soils.

Opportunities for the Introduction of Pigeon Peas into Smallholder Farming Systems in Zimbabwe
PAUL MAPFUMO¹, PARAMU MAFONGOYA² AND SHEUNESU. MPEPEREKI¹

1. Department of Soil Science & Agricultural Engineering, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe.
2. Zambia-ICRAF Project, P.O. Box 510089, Chipata, Zambia e-mail: pmapfumo @ compcentre.uz.ac.zw

Abstract
Smallholder agriculture in Zimbabwe is characterised by maize monoculture. Several other crops, especially legumes, have received little attention despite their agronomic potential and nutritional value. The pigeon pea is a well-known multipurpose crop in subsistence agriculture, yet none of its useful attributes have been exploited in Zimbabwe. In this study, the feasibility of intervening with pigeon peas in smallholder farming systems was investigated in Mukarakate area of Murehwa Communal Lands and revealed a limited use of legumes in both human nutrition and soil fertility management. The lack of a well co-ordinated agenda to promote legume production, and a poor agronomic performance by the currently grown legumes because of the low fertility and pH of the soils were identified as some of the main constraints. Limitations imposed by the biophysical and economic environments in agricultural production at local level were also identified. The potential place of pigeon peas as perceived by farmers is discussed in the context of on-going pigeon pea experiments designed to investigate the potential contribution of this crop to soil fertility.

An Assessment of Alternative Perennials for use in Agroforestry Systems of Small Holder Farmers
SAM MUCHENA

African Centre for Fertilizer Development, P O Box A469, Avondale, Harare
e-mail: [email protected]

Abstract
Current crop production systems in Zimbabwe are vulnerable, especially in drought years, as the country is now and again affected by the El Niño phenomenon. The majority of the population live in drought-stricken areas with infertile soil where poverty is a major problem. Agricultural strategies should aim to achieve the multiple goals of the farmers, which include household food security, increased cash incomes, increased crop diversity, and an improvement in soil fertility. The AFCD is making plans to collaborate with others to promote the adoption, through participatory approaches, of sustainable farming systems in the communal areas of the country. These systems emphasise the improvement of farm management skills in order to use fertilizer more efficiently, to control pests and diseases, and soil and water conservation. This paper describes the underlying principles for the development of sustainable farming systems and the ACFD's experience with agroforestry trees like castor oil, jatropha, and pigeon peas, that minimise the risk of soil degradation and provide other benefits.

The Forestry Extension Services Contribution Towards Agroforestry for Soil Fertility Improvement
JUDITH T. NYAKABAU

Forestry Extension Services, Forestry Commission, P.O. Box HG 139,Highlands, Harare

Abstract
In Zimbabwe there is a significant loss of forest cover every year because of land clearing for agriculture and human settlement. These factors will continue to threaten forests unless means of co-existence are devised. Current farming methods involve the massive mining of soil and erosion of soil nutrients. Using agroforestry to improve soil fertility is one possible remedy to this problem and this paper highlights some successes in using agroforestry. It reports on one project in Masvingo and another in Zaka where both farmers have used Leucaena to improve soil fertility and to provide fodder for animals.

Improved Fallows for Sustainable Food Security in Eastern Zambia
FREDDIE KWESIGA

Regional Coordinator, SA-AFRENA and the Zambezi Basin Agroforestry Project, International Centre for Research in Agroforestry (ICRAF), Makoka Research Station, P.O. Box 134, Zomba, Malawi¹

^1.Present address: ICRAF Regional Office, P.O. Box MP 163, Mount Pleasant, Harare, Zimbabwe e-mail: [email protected]

Abstract
In most of Southern Africa, crop yields are marginal because of the low intrinsic soil fertility, the limited use of inorganic fertilizers and the declining use of traditional fallows. To increase soil fertility and food production sustainably, soil fertility must be increased. The inclusion of agroforestry trees in agro-ecosystems is one of the ways to provide the essential organic matter and mineralisable nutrients. In Eastern Zambia ICRAF researchers and their counterparts in the national agricultural system have developed a promising agroforestry alternative to traditional fallows. It involves planting Sesbania sesban as 2 to 3 year improved tree fallows in N-depleted fields. Thereafter, the trees are clearfelled and all the twigs and leaf litter incorporated in the soil. The result is a doubling or even a quadrupling of maize yields. In addition, these planted leguminous tree increase biologically active pools of soil organic matter and the rate of release of plant-available nitrogen from soil organic matter. The results suggest that tree species differ greatly in their effects on soil organic matter pools and nitrogen availability to subsequent maize crops.

Introduction of Improved Fallows of Sesbania and Pigeon Pea under a Maize Stand
C. NYAKANDA¹, I.K. MARIGA¹, B.H. DZOWELA², H. MURWIRA³ & N. TINOFIREYI¹

^[1]Crop Science Department, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare.
² SADC-ICRAF Agroforestry Project,P.O. Box CY 594, Causeway, Harare.
³ Chemistry and Soils Research Institute, Dept of Research and Specialist Services, P.O. Box CY 550, Harare

Abstract
The productivity of soils in smallholder agriculture can be improved by the introduction of short-duration (2-5 years) improved fallows. The availability of land is a constraint, so these improved fallows should be designed so that farmers can derive other benefits over the duration of the fallow phase. The introduction of improved fallow species of Sesbania sesban, Cajanus cajan and a 50:50 mixture of the two species under a maize stand in the first year of fallow establishment had no effect on maize grain yield, neither was the growth of the tree species curtailed. The grain yields of pigeon peas grown alone or under maize were similar but the tree species affected the weight of maize stover. Establishing these tree fallows under annual crops during the first year of fallow establishment may induce farmers to use this approach since they can harvest some grain in one of the years during the fallow phase.

Nutrient Balances in Improved Fallows of Sesbania sesban in a Maize-based System in Sandy Soils of Zimbabwe
CHINANISO CHIBUDU

Farming Systems Research Unit, DR & SS, P O Box CY 550, Causeway, Harare

Abstract
A partial static nutrient balance for improved and natural fallow was constructed using data from the literature and trials conducted in the Mangwende communal area, Zimbabwe, from 1994-97. The objectives were to determine the effect of improved fallows of Sesbania sesban and natural fallows in sustaining and/or maintaining the nutrient resource and to identify improved management options for depleted lands. Net positive nutrient balances for nitrogen ranging from +36.6 to +120 kg ha^-1 year^-1 nitrogen (N) were obtained in maize following S. sesban after 1 or 2 years, in fertilised and unfertilised maize plots in the first year of cultivation. The nutrient balance of phosphorus (P) was negative in unfertilised plots following S. sesban in contrast to fertilised plots. Negative nutrient balances, ranging from –2.6 to –11.4 kg ha^-1 year^-1 for N and –0.4 to –1.6 kg ha^-1 year^-1 for P, were obtained from continuously unfertilised maize plots during the three seasons. The results suggest that nutrient depletion is taking place but the magnitude was low because of small nutrient losses due to the low yields of maize. Although there was a positive nutrient balance for N and P in a fertilised maize crop after natural fallows, the magnitude was much lower than when S. sesban was incorporated into the system for two years. The maize yield improved with S. sesban fallows resulting in a high nutrient off-take, which was offset by biological nitrogen fixation. A combination of improved fallows and inorganic fertilizers seems to be needed to maintain positive nutrient balances for N and P.