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Greenland, 1960; Sanchez, 1976; Volkoff et al., 1989; Gerold, 1995). In the study area, the topsoil structure and porosity changes may be the most important soil degradation characteristics and the main cause of field plot abandonment and shift. Results show that presently, the shifting characteristic of the cropping system is defined in two directions: - The first direction is that of moving within natural fallow plots of different ages. This constitutes a rotational system, which is common practice nowadays. It concerns mainly food crop fields. 76% of the food crop fields in the area rely on this rotational system. - The second direction is that of agricultural fields expanding into undisturbed forestlands. This is the traditional pure expansive system, which constitutes more threat to forest conservation and sustainable management system than the rotational system. This system which concerns 24% of the food crop fields is practised mainly for cucumber (Cucumeropsis mannii) production and for the establishment of semi-industrial farms by the elite. For this system, an average of 2200 m² of new forest land is opened per household per year in the TCP area. This average corresponds to about 300 m² per inhabitant. The Ebimimbang plains and Mvié uplands have the highest rate of forest encroachment per year and per household with values of 2450 m² and 2650 m² respectively. The higher rates in these two units are probably because the land is better accessible for agriculture, leading to an increase in population, and because the areas have been commercially logged several times (Table 4.2). Table 4.2. Population variation with landform units in the TCP area Plains and Uplands of Ebimimbang and Mvié Hills and Mountains of Ebom and Nyangong Population 1593 992 Household 178 137 4.3.2 Relationship between soil degradation and crop yield Because of the absence of any significant difference between 0-10 cm and 10-20 cm slices, results of these analyses are presented for the top 0-20 cm soil layer. The analysis took into account the two main soil types of the study area. Multiple linear regression coefficients from these analyses are shown in Table 4.3. Table 4.3. Multiple linear regression equations of various crop yields as functions of physico-chemical soil properties in 0-20 cm soil slice (at p
These results show that in the area, the biomass yield of maize and groundnut is controlled by chemical soil properties; while grain yield is controlled mainly by physical soil properties. Cocoyam yield correlates positively with soil CEC and the level of the organic matter, but negatively with the ash effect measured by the soil calcium content (Table 4.3). These results are of utmost importance in making decision regarding the type of fertiliser or amendment to be used when agricultural intensification is to be considered with fertilisation inputs. 4.3.3 Soil degradation and agricultural field expansion In shifting cultivation system, because of yield decline during the cropping period, fields are abandoned and new fields are cleared in a developed fallow or in an undisturbed forest. Soil degradation and weed infestation are reported to be the main reason for yield decline (Nye and Greenland, 1960; Sanchez, 1976; Volkoff et al., 1989; Gerold, 1995). In the study area the topsoil structure and porosity changes seem to be the most important causes of field plot abandonment. 4.3.4 Relationship between commercial logging and shifting cultivation activities Shifting cultivation and commercial logging are the two main human activities of the study area, which contribute to deforestation and represent threats to forest conservation. Although logging is mainly an industrial and temporary activity of logging companies, it has a strong influence on the shifting cultivation of rural population in the area. The relationship between the two activities is highlighted in the following aspects: - Farmers use roads and logging tracks to gain access to new fields for shifting cultivation in the virgin forest. This is confirmed by the pattern of agricultural land distribution along the road sides. - The presence of logging companies means that the logging personnel will buy food crops in the villages. This obliges farmers to increase their production by increasing the area under cultivation. - Logging and farming activities are both contributing to degradation of lands. Bulk density and aggregate stability of the top A-horizon of Oxisols were significantly higher (p 180 b (n = 12) N.B. a and b are significantly different at p
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Farming systems in the evergreen fo
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ABSTRACT Nounamo, L. and Yemefack,
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4.3.4 Relationship between commerci
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PREFACE This report presents the fi
Page 10 and 11: stability and structure, and the de
Page 12 and 13: (calcium), le pourcentage de satura
Page 14 and 15: Figure 1.1. Location map of the TCP
Page 16 and 17: 600 28 500 27 Rainfall (mm) 400 300
Page 18 and 19: low pH (3.8 to 5) and a high clay c
Page 20 and 21: Characteristics of the four sub-sit
Page 22 and 23: 2.2.7 Household labour study The st
Page 24 and 25: Roads may temporarily be closed, du
Page 26 and 27: swamps and valley bottoms are also
Page 28 and 29: Table 2.6. cont’d Species Ewondo
Page 30 and 31: dispose of land near the village, o
Page 32 and 33: The heat may, however, reduce the g
Page 34 and 35: is an activity practised by nearly
Page 36 and 37: The crop production activity takes
Page 38 and 39: Table 2.17. Priority socio-economic
Page 40 and 41: 3 ASPECTS OF SOIL DEGRADATION UNDER
Page 42 and 43: 3.2.3 Laboratory soil analyses Soil
Page 44 and 45: The magnitudes of changes are inver
Page 46 and 47: as it is practised in shifting cult
Page 48 and 49: 15 years. The vegetation evolves th
Page 50 and 51: Organic matter. Organic carbon incr
Page 52 and 53: Microbial Biomass Carbon C (ugC/g s
Page 54 and 55: processes on soil chemical properti
Page 56 and 57: soil, result in loss of soil aggreg
Page 58 and 59: 4 TRENDS IN FIELD EXPANSION AND SOI
Page 62 and 63: 5 SOLUTIONS TO FARMERS’ PROBLEMS
Page 64 and 65: Integrated Nutrient Management meth
Page 66 and 67: REFERENCES Almy, S.W., Besong, M.T.
Page 68 and 69: Prat, C. (1990). Relation entre ér
Page 70 and 71: ANNEX 2: CHECKLIST FOR THE EXPLORAT
Page 72 and 73: ANNEX 4: AGRICULTURAL LAND EXPANSIO
Page 74: ANNEX 6: AGRICULTURAL LAND EXPANSIO
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