Soil Characterization And Effects Of N, P And K On The Growth, Yield And Root Quality Of Cassava (Manihot Esculenta Crantz) In The Lake Zone Of Tanzania

EXTENDED ABSTRACT 

Cassava (Manihot esculenta Crantz) is a main staple food crop in many African countries including Tanzania, but to other countries in Asia is a cash and industrial crop. The major cassava growing areas in Tanzania includes the Lake Zone (Mwanza, Kagera, Mara, Simiyu, Geita and Shinyanga), Southern zone (Mtwara, Ruvuma and Lindi), Eastern zone (Coast, Tanga and Morogoro) and Zanzibar (Pemba and Unguja). In Tanzania cassava is cropped continuously in the same field with no or little addition of agricultural inputs and this has resulted in soil nutrients mining and consequently low yields. To increase and sustain cassava production and productivity, soil characterization, fertility status assessment and appropriate soil and crop management practices are inevitable. This will complement the breeding program efforts in generating improved cassava varieties. The main objectives of this study were to characterize, assess the initial soil fertility and the effects of N, P and K on growth, yield, and root quality of cassava (Manihot esculenta Crantz) in three selected cassava growing areas in the Lake Zone of Tanzania. This study was conducted during 2016/17 and 2017/18 growing seasons, in three major cassava growing sites which were Runazi village in Biharamulo district, Kijuka village in Sengerema district and Nyakiswa village in Butiama district in the Lake Zone of Tanzania. One representative soil profile from each study site was excavated. The morphological soil properties were assessed and the soil profile described according to the FAO guidelines of soil profile description (FAO, 2006). Collected soil samples from each site were, air-dried, crushed and sieved to pass through 2 mm sieve then taken to the International Institute of Tropical Agriculture Laboratory in Dar es Salaam for analysis. The physical and chemical properties of soils were categorized and rated according to the Booker Tropical Soil Manual (Landon, 2014). iii Soils were classified according to the Soil Survey Staff (2014) up to the subgroup level and to the IUSS Working Group WRB (2015) reference soil groups (RSG) to TIER 2 level using the soil morphological and laboratory data. The topsoil was used to assess the fertility status of each study sites and rated according to Landon (2014). The effects of fertilizers on growth, yield, and root quality of cassava (Manihot esculenta Crantz) were assessed using eleven N, P and K treatments laid down in a randomized complete block design (RCBD) with four replicates in a form of nutrient omissions. Treatments consisted of the full rate NPK (150 kgha-1 N, 40 kgha-1 P and 180 kgha-1 K), and half-rate NPK (75 kgha-1 N, 20 kgha-1 P and 90 kgha-1 ). The test crop was “Mkombozi” cassava variety which is an improved high yielding and early maturing. Cassava growth, yield and root quality data were collected at twelve months (12 MAP) after planting. Cassava plants from the net plot were uprooted, weighed and grouped into above-ground biomass and below-ground biomass at harvest. The growth parameters namely the lignified stems, green stems, old planting stakes, and fresh leaves were weighed and expressed in kilograms (tha-1 ). Plant height was measured in centimetre (cm) from the top of the ridges up to the top branches of the cassava plant.