The use of mixed systems for agricultural and forestry production is by no means new. In pure agricultural systems the sowing of mixed annual crops has been a common farmer response to risk from climatic uncertainties to the need for diversity of food crops and to pragmatic observations of beneficial interactions between species. In the humid tropics, whether highland or lowland, sophisticated tree-crop mixtures have been developed over centuries using many species and where a wide variety of benefits are obtained. In the drier parts of Africa trees have formed important components of grazing systems, or have been left deliberately for their benefits in cultivated land. A simpler system, the use of agriculture crops for assisting in the establishment of forest plantations (taungya) is widespread, and in Africa as elsewhere shifting agriculture provided, in the past, a sustainable land-use system which is only now breaking down under the pressure of increasing populations.
Tag: mixed farming
A static model of nutrient flow on mixed farms in the highlands of western Kenya to explore the possible impact of improved management
Currently there is much interest in the potential role of agroforestry in the mitigation of nutrientdepletion in sub-Saharan Africa. Using data from farm surveys and trials static models of nutrient flowfor existing farm systems and improved agroforestry systems were constructed. These included boundary plantings of trees, hedgerow intercropping for green manure or fodder, and a well-managed zero-grazing system with moderate fertiliser inputs. The objective was to explore the possible impacton nutrient budgets of improved management options. Major nitrogen (N) losses (70% of total farmloss) occurred in the field and hedgerow compartments, principally through leaching and denitrification, which exceeded 60 kg N/ha per annum in all systems. However, there was uncertainty in predicted net mineralisation and the potential amounts of soil-N losses, and the study indicatedsubstantial potential for N mineralisation in deep subsoils. In contrast, phosphorus (P) was efficiently conserved in the farm system, and moderate additions of inorganic P fertilisers could maintain soil-P stocks. Net soil nutrient balances ranged from –39 to –118 kg N/ha per annum and from –7 to +31 kgP/ha per annum in the different simulated systems. N inputs through biological N fixation and deep N capture were significant in agroforestry systems (up to 122 kg N/ha per annum), but when trees were used for production purposes these additional inputs were offset by increases in consumable N harvested (grain, wood and milk) which ranged from 35 to 195 kg N/ha. Improved manure management reduced soil-N deficits by 70 kg N/ha per annum in a zero-grazing system with a highmanure flux. Research priorities for the humid highland farming systems include the quantification and dynamic modelling of (1) N mineralisation and N dynamics throughout soil profiles, (2) spatial and temporal patterns of N uptake by trees in agroforestry systems, and (3) nutrient budgets inlong-term systems trials
Soil fertility management in semi arid areas of east and southern Africa
The Arid and Semiarid areas in Sub-Saharan Africa occur mainly around the latitude 10 -15 N IN west Africa and roughly 10 -30S in Southern Africa.In addition there is also a large arid and semi-arid region in The Horn of Africa and East Africa.Another largo dry region exist in South-Western and South-Estern Africa, consisting of semi-arid strip that runs roughly North and South inland in Namib Desert, eastwards in a broad belt through Botswana, and then south through the center of South Africa.Smaller semi-arid areas are also found in Zimbabwe,Mozambique and Madagascar.
Agroforestry is a form sustainable forest management: lessons from Southeast Asia
Agroforestry as land use based on planted trees, provides productive and protective(biological diversity, healthy ecosystems, protection of soil and water resources,terrestrial carbon storage) forest functions that societies care about in the debate onsustainable forest management. Yet, the trees planted in agroforestry systems areexcluded in formal definitions and statistics of ‘forestry plantations’ and overlooked inthe legal and institutional framework for sustainable forest management. A paradigmshift is needed in the forestry sector and public debate to redress this oversight. Weexamine five issues that hinder a regreening revolution based on farmer tree planting tocontribute to sustainable forest management. First, issues of terminology for forests,plantations and reforestation are linked to land tenure and land use restrictions. Second,access to high quality planting material of proven suitability remains a challenge,especially at the start of a farmer-tree-planting phase of a landscape. Third,management skill and information often constrain production for high market values.Fourth, overregulation often restricts access to markets for farmer grown timber andtree products, partly due to rules intended to curb illegal logging from natural forests orgovernment plantations. Fifth, there is a lack of reward mechanisms for environmentalservices provided by agroforestry. Current relationships between agroforestry andplantation forestry are perceived to be complementary, neutral or competitive,depending on the ability of (inter)national policy frameworks to provide a level playingfield for the provision to society at large of productive and protective forest functions.In conditions where large-scale plantations operate with substantial governmentsubsidies (direct or indirect, partly justified by environmental service functions), incontrast to non-existent or minimal subsidies for agroforestry, the potential to producewood and simultaneously provide for many forest benefits and ecological services withagroforestry is placed at a disadvantage, to the detriment of society at large