*2.1.1 Geographical location*

The study was conducted in Kilombero District located in Morogoro Region between 08o 00′ 16" South and 36o 04′ 364″ East with elevation ranging from 262 m to 550 m above the sea level, See. Administratively, Kilombero District has five divisions, 19 wards and 46 villages. The district is bounded by Kilosa District in the North, South East by Ulanga district, South west by Iringa region as well as in the West and the East by Lindi Region [11].

## *2.1.2 Climate*

The climate in the study area is marked by wet and dry seasons which are further categorized into four sub seasons, hot wet season from December to March, cool wet season April to June, cool dry season July to August and hot dry season September to November. The area receives between 1 200 and 1 800 mm of rainfall per year and temperatures ranging from 26 to 32°C [12].

### *2.1.3 Land use*

Generally, the land use is categorized as village land, reserved land and general land as defined in the Village Land Act 1999 [13]. Meanwhile, Kilombero is considered as one of the fertile spots in Tanzania. The main economic activities in the area include cash crops, food crops, petty trading and fishing in Kilombero River [11]. Overall cereals of the Coast, such as rice, millet, and maize, are grown widely. Also, vegetables such as sweet potatoes, yams, ground-nuts, melons,

*Carbon Sequestration in Agroforestry Technologies as a Strategy for Climate Change Mitigation DOI: http://dx.doi.org/10.5772/intechopen.100036*

pumpkins and cucumbers, and many other excellent articles of food. Tobacco is grown very abundantly, sugar-cane, the castor oil plant, cocoa and cotton, are also cultivated [14].

### *2.1.4 Population*

According to the 2012 census the population of Kilombero was 407 880 with male 202 789 and female 205 091 [15]. This area is currently experiencing a doubling of the human population over the years. It has been demonstrated that within Tanzania population growth results in environmental degradation [16]. This increase of population has resulted from migration from various places for cultivation due to soil suitability for farming and livestock keeping migration.

#### **2.2 Methods**

### *2.2.1 Reconnaissance survey*

Pre-visiting was conducted to as well as pre-testing of inventory equipment's. This was also conducted so as to familiarize with the study area and observe the nature of the agroforestry farmland.

### *2.2.2 Study design*

The research design for this study was descriptive and cross-sectional. Descriptive design was involved as it gives thorough information concerning agroforestry technologies. Also, cross-sectional design was chosen as data were collected at once without repetitions.

#### *2.2.3 Data collection*

A total of 90 farm land were visited in this study. Data for above ground biomass were species, number of trees, Diameter at breast height (DBH), height and diameter at 0.3 m for cocoa trees [17, 18]. A systematic sampling design was expected to be used but during the field all the encountered farms were less than two hectare and there for all the trees within the farmland were all measured and all the farms were considered as a plot [19]. Height were measure using Suunto hypsometer and diameter using calipers.

#### *2.2.4 Data analysis*

#### *2.2.4.1 Biomass and carbon stoking*

Information obtained from the biophysical survey mainly inventory data was recorded in Microsoft excel for biomass calculation and carbon stock. Allometric equations were used to convert the field measurement attribute mainly heigh and diameter into stand biomass. Since in agroforestry there is diversification of wood perennial, then general allometric model for Cultivated land herbaceous, mixed tree, intercropping and grain crops (for all tree species) was used for the trees without specific equation. Most of these models have been developed for Tanzanian tree species and vegetation types [20]. Carbon stock was computed as the product of Total Biomass and factor of 0.5 [21].

Below are the species specific allometric equations and general allometric equation for computing the above and below Biomass [20, 22]

Tectona grandis

$$\mathbf{AGB} = \mathbf{0}.\mathbf{33556} \times D^{2.1691} \tag{1}$$

$$BGB = 0.027 \Re \times D^{1.7430} \times Ht^{0.7689} \tag{2}$$

Theobroma cacao

$$AGB = \mathbf{0}.\mathbf{1}\mathbf{2}\mathbf{0}\mathbf{8} \times d^{1.98} \tag{3}$$

$$BGB = AGB \times 0.25\tag{4}$$

Cocos nucifera

$$AGB = \text{3.7964} \times Ht^{1.8130} \tag{5}$$

$$BGB = \mathbf{13.5961} \times Ht^{0.6635} \tag{6}$$

Cashew nuts

$$AGB = 0.3152 \times D^{1.7722} \times H t^{0.5003} \tag{7}$$

$$BGB = AGB \times 0.25\tag{8}$$

For other tree then general allometric equation for Cultivated land herbaceous, mixed tree, intercropping and grain crops (for all tree species) was used.

$$AGB = 0.051 \times \left(D^2 \times Ht\right)^{0.93} \tag{9}$$

$$\text{BGB} = \text{AGB} \times \text{0.25} \tag{10}$$

For carbon estimation then for each tree Total Biomass (TB) which is sum of AGB and BGB was computed by the equation below.

$$\text{Carbon Stock} = \text{TB} \times \text{0.47} \tag{11}$$

where ABG = Above ground biomass BGB = Below ground biomass D = diameter at Breast height d = diameter at 0.3 m above the ground TB = total biomass
