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3.2.3 Laboratory soil analyses Soil samples were analysed at the IRAD soil laboratory in Nkolbisson for routine analyses: - pH water and KCl (1:2.5 ratio); - organic Carbon (Walker and Black method); - total Nitrogen (Kjeldahl digestion); - available Phosphorus (Bray II method); - exchangeable bases (extraction with 1M ammonium acetate solution); - Cation Exchange Capacity (extraction with 1M ammonium acetate solution at pH7); - Exchangeable acidity (leaching with 1M KCl and titration by 1M NaOH); - particle size distribution (Robinson pipette method); and - bulk density (oven dry at 105ºC). - Aggregate stability was determined at Tropenbos laboratory in Kribi by Water-Drop Impact method (Imeson and Vis, 1984). Soil samples for microbial biomass carbon were analysed at the microbiology laboratory of Yaoundé I university. Microbial biomass carbon was measured by fumigation-incubation method (Jenkinson, 1976; Anderson and Ingram, 1993). 3.3 RESULTS AND DISCUSSION Soils surveys have shown that soils of the TCP research area can be grouped into two main soil types. The two soil types are “Ebimimbang soils” and “Nyangong/Ebom soils”, which fall respectively into Ultisols and Oxisols Orders of the USDA soil taxonomy system (Soil Survey Staff, 1992). The two soil types are distinguished by many soil properties. However, clay content, pH and organic matter appear to be most important properties controlling their differences. This in fact, may be a normal consequence of the difference in geology, elevation, physiography and microclimate as described in Sections 1.3.1 and 2.2.1. The following results are presented for rates and trends of land use effects in each soil type. No general comparison was made for the two soil types, since they showed no differences in trend analyses. The only one land use system that receives sometimes organic fertilisation or amendments from farmer’s kitchen (see Section 2.3.3) was not taken in consideration in this study (i.e. home gardens). 3.3.1 Food crop fields and soil property changes The analysis of soil behaviour in traditional food crop field takes into account two phases. The first phase concerns clearing and burning of the vegetation, which causes sudden changes in the soil. The second phase deals with the slower changes in soil physical, chemical and biological properties during cropping and fallow. Clearing and burning Burning is an essential element of the farming system. It is the only way the farmers can properly clear the ground of the large mass of slashed undergrowth and felled trees, and make it accessible for tillage or for planting of food crops. Other beneficial effects of the burning as reported in the literature are killing of weed seeds in the topsoil and of stump sprouts which would shade out crop species, and partial sterilisation of the soil (Nye and Greenland, 1960; Sanchez, 1976). In addition, this practice has remarkable positive as well as negative effects on soil surface properties. Table 3.1 presents results of soil property changes from fallow to food crop fields. Soils were sampled at planting. Soil chemical property changes. Ashes from burned vegetation at the beginning of the cropping period act as liming materials and significantly (P
Table 3.1. Soil property changes from fallow to food crop field after burning. 0-10 cm slice on sandy topsoil (Ebim) 0-10 cm slice on clayey topsoil (Nyan) Crop field types Crop field types CF BF FF CF BF FF fa fcf fa fcf fa fcf fa fcf fa fcf fa fcf pH 6.9 7.2 5.4 6.8 5.7 6.8 4.5 4.9 3.9 4.6 3.6 4.3 OC (%) * 2.6 1.8 2.3 2.5 2.1 2.1 3.1 2.6 3.3 2.9 3.6 3.3 C/N ratio 8.8 12.5 9.9 13.0 12.1 12.6 10 14 10.5 13.5 13.7 12 P av. (ppm) 14 33 4 23 6 17 8 17 7 15 7 20 Ca (cmol / kg) 9.3 12.6 4.6 11,3 5.8 6.5 2.3 3.4 1.0 3.1 0.5 2.7 Σbases (cmol / kg) 11.8 14.4 6.6 13.7 7.9 9.3 3.9 5.2 2.0 4.8 1.6 4.6 Al 3+ (cmol / kg) 0.0 0.0 0.0 0.0 0.0 0.0 1.3 0.5 2.4 1.0 3.5 2.5 CEC (cmol / kg)* 6.7 6.8 4.5 9.6 9.6 8.9 9.9 9.3 9.1 11.9 14.8 15.8 BS (%)* 99 99 97 98 82 96 54 81 28 72 16 52 B.d. (g / cm 3 ) 1.21 1.35 1.16 1.23 1.03 1.17 1.11 1.10 0.99 1.05 0.89 0.96 SS (water-drops) 68 13 78 51 136 35 144 133 182 166 142 165 Clay (%) * 13 15 17 17 15 10 33 28 33 31 39 37 MB (µC / g soil) - - - - - - 976 901 1263 755 1023 529 Keys: Ebim = Ebimimbang soils; Nyan = Nyangong/Ebom soils CF = Chromolaena Fallow OC = Organic Carbon Σbases = sum of bases BF = Bush Fallow P av. = available phosphorous Ca = Calcium FF = Forest Fallow BS = Base Saturation Percentage B.d. = Bulk density fa = fallow soil MB = Microbial biomass SS = Structural Stability fcf = food crop field CEC = Cation Exchange Capacity * Effect of burning not significant at p
Page 2 and 3: Farming systems in the evergreen fo
Page 4 and 5: ABSTRACT Nounamo, L. and Yemefack,
Page 6 and 7: 4.3.4 Relationship between commerci
Page 8 and 9: 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 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 60 and 61: Greenland, 1960; Sanchez, 1976; Vol
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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