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Contents........................................ ............. .... i A cknow ledgem ents ........................................................................................... A cro nym s............................................................................................................. Chemical compounds........................................................................................... Executive summary ............................. .............................................................. vii 1 Introduction ............... .............................................................1. 1.0 Sustaining agricultural production................................................................................................... 1 1.1 Land degradation .................................................. . ..................................................... .......... 1 1.2 Soil fertility............................................ . ......................................... ............... 2 1.3 The need for soil surveys.................. ................................................................................ 2 1.4 Need for soil fertility assessment................................................................................................ ... 3 1.5 Soil fertility problems in the Lake Victoria basin .................................................................... 3 1.6 Addressing the Kusa community action plans.......................:.................................................3 2 Assessing soil fertility and management in Kusa............................................... 5 2.1 The study area ........................................................................................ 5 2.2 Field soil surveys.................................................................................................................... .......... 6 2.3 Laboratory soil analysis............................................................................................................. 8 2.4 Mapping of the soils....................................................................................................... 8 2.5 Data analysis ........................................................................................................................... .......... 9 2.6 Determining fertilizer and manure recommendations................................................... 9 2.7 Farmers' exposure tour to Mt. Kenya region............................................................................ 10 2.8 Dissemination of study findings to farmers in Kusa........................................ ............... 10 3 Soil fertility in the Kusa profile: findings .......................................... ............. 11 3.0 Soils data.................................... .............................................................................................. 11 3.1 A general overview of the soils of Kusa........................................ ........ ........... ............. 12 3.2 Distribution of the soils............................................................. ................................ .......12 3.3 Farm er interview s .............................................................. ....................................................... 15 3.4 Socio-economic factors in soil fertility ............................................................................18 4 Effects of soil properties on sustainable crop production...................................21 4.0 Soil characteristics and fertility .................................................................................................... 21 4.1 Critical values of major soil properties affecting fertility.....................................................21 4.2 Impacts of physiography on soil fertility in Kusa..................................................................21 4,3 Im pacts of clim ate ........................................ .............................................. ..........................21 4.4 Soil physical properties ........................................ ......................... ................................ 23 4.5 Soil organic m atter.................................. ..... . ....... .......... .... .... ........................................23 4.6 Macro and micro nutrients............................................................................................................ 24 4.7 Limiting chemical conditions...................................................................................................... 27 5 Impacts of soil management.................................................. ........................29 5.0 Soil management and fertility .................................................................................................. 29 5.1 Land sizes and use ............................... ............................. ..... ........................ 29 5.2 Crop types and management ...................................................................................................29 5.3 Crop yields .................................................... .... ................ .................... ......... . 30 5.4 Impacts of climate................................. ........................................................................................ 30 5.5 Role of livestock in soil fertility management........................ ......................... 30 5.6 Use of inorganic fertilizers ...................................................................... .........................31 5.7 U se o f m anures ......................................... . ............................................................................... 31 5.8 C om p o sting .................................................................... .. .. .................. .............................. 33 5.9 What about green manuring?.................................................................... .......................33 5.10 Farmer perceptions about soil fertility ............ ............................................ .........................34 6 Integrated approaches to soil fertility management................................. .....35 6.0 Why integrated approaches........................................................................................................... 35 6.1 Tillage....... .....................................35 6.2 Soil erosion and conservation.................................................................................................. 36 6.3 Water harvesting and maagement........................................................ .........................36 6.4 Irrigation and drainage........................................... ..... ............................................... 37 6.5 Sustainable farming alternatives ................................................... ................................... 38 6.6 A groforestry............................ ............ ...................................................................................... 39 6.7 Farmer-to-farmer learning................................................................................................... 39 6.8 Socio-economic implications .................................................................................................. 40 7 Conclusions and recommendations....................................................................41 7.1 Research methodology......................................................................................................... 41 7.2 Physiography and climate .....................................................................................................41 7.3 Soil physical properties .................................................... .....................................................41 7.4 Soil organic matter....................................................................................................................42 7.5 Macro and micro nutrients...................................................................................................... 42 7.6 Soil pH and sodium contents................................................. ..............................................42 7.7 Crop husbandry................................................................................... ...............43 7.8 Livestock and soil fertility ........................................................................................................ 43 7.9 Inorganic fertilizers.................................... .............................. .................................43 7.10 Manures and composting ...... ................. ...................................................44 7.11 Im pacts of tillage................................................ ........ ... ... ....... ... ................... ........ 44 7.10 Soil erosion and conservation...................................................... ................................... ..44 7.13 Water harvesting and management.......................................................................... ...............45 7.14 Irrigation and drainage................................. ................. ........... ....................45 7.15 A gro forestry...................................................................................................................................... 45 7.16 Farmer exposure tour.................................. ... ...... ........................46 7.17 Socio-economic implications ................................... ......................... .. ..............46