Baseline Report Yala and Nzoia River Basins

Lower Nzoia

The Lower Nzoia block is located on the Kano?? lake plain of Lake Victoria in Siaya and Busia districts. The block contains fifteen sub-locations. This block is bisected by the Nzoia River is characterized by generally flat terrain (2 to 6% slopes), a few shallow depressions, wetlands and flood plains with small permanent streams. There are several large hills in the western part of the block.
Most of the block is dedicated to subsistence agriculture, with crops typical of low elevations in western Kenya. Farmers principally grow maize, bean, sorghum, cassava, and potatoes. There are many wetlands inand floodplains in the southern part of the block, and thiswhich is an area that frequently floods as thewhen River Nzoia bursts it banks in every rainy years (e.g El Niño years). The soils have high concentrations of sodium and are highly susceptible to erosion.


Figure 6.1. Administrative map of the Lower Nzoia block. The blue dots are the sampling points for the biophysical survey; socioeconomic samples are shown by triangles.

1. Biphysical baseline data summary

   1. Topography

The area Lower Nzoia is characterized by flat terrain with slopes ranging between 1 and 6% (Figure 6.2; Table 6.1). The block is located on the lake plain and therefore has little relief. There are a few hills in the north western portion of the block. Only Cluster 3 has any significant relief, with 60 % of the plots sampled having slopes > 10% and an average slope of 17%. The other clusters in the western half of the block had a few steep areas, but overall slopes were gentle in these areas. The eastern half of the block has a flat terrain. The block is bisected by the Nzoia River which traverses from east to west.


Figure 6.2. Topographic map of the Lower Nzoia block

Table 6.1. Average slope, slope range, and incidence of steep slopes.

Cluster	Average slope (%)	Slope range (%)	No. values > 10%
1	3.13	0.87 - 18.22	1
2	1.79	1.31 - 2.18	0
3	17.59	1.75 - 43.05	6
4	6.05	2.18 - 16.5	2
5	2.75	1.31 - 6.10	0
6	5.20	0.87 - 28.4	1
7	2.88	1.31 - 5.23	0
8	6.04	1.75 - 23.34	2
9	6.75	3.49 - 13.92	2
10	2.09	0.87 - 4.80	0
11	3.45	1.31 - 4.80	0
12	2.23	1.75 - 2.62	0
13	4.19	2.62 - 6.10	0
14	3.75	2.18 - 5.67	0
15	3.67	1.40 - 5.23	0
16	3.97	2.62 - 5.23	0

2. Soil texture and soil depth restrictions

The soil texture in this area is fairly homogenous and either clayey or clay loam (Table 6.2). The soils tended to have slightly higher silt contents in the eastern part of the block.
Table 6.2. Soil texture (% of samples).

Clay	Clay loam	Loam	Loamy sand	Sandy clay loam	Sandy loam	Silty clay	Silty clay loam
66	46	10	1	1	7	23	6

Soil depth restrictions were widespread across the block, with 27% of the subplots sampled showing restrictions within the first 50 cm and 16% of the subplots showing restrictions within the first 20 cm. Clusters 1, 3, 4 and 9 have very high incidence of depth restriction. Clusters 8,10,11, and 12 have almost no depth restrictions.

Table 6.3. Incidence of depth restrictions per cluster (values =

% of subplots per cluster with depth restrictions; n = 40).

Cluster	Shallow (≤ 20 cm)	Deep (> 20 cm)
1	43	28
2	3	18
3	20	40
4	25	25
5	13	15
6	15	15
7	3	None
8	None	None
9	38	30
10	None	None
11	15	3
12	3	3
13	33	18
14	15	13
15	18	28
16	10	18

3. Vegetation and land use

Farming is the major land-use and drives land cover in the block (Figure 6.3; Table 6.4). Agriculture is dominated by cereal production, but there are also large areas with perennial grasses for livestock grazing. The largest allocation of land in this block was for farmland. However, a significant portion of this farmland was found to be temporarily abandoned because of flooding. Forage land and perennial grasslands also make up a significant portion of the block. The dominant species in the area are as follows:

1. 
   Sporobulus pyramidalis: annual grass; low forage value;
   
2. 
   Digitaria ciliaris: annual grass; low forage value;
   
3. 
   Digitara gazensis: perennial grass; high quality forage
   
4. 
   Eragrostis aspera: annual grass; moderate forage quality;
   
5. 
   Eragrostis superba: perennial grass; good quality forage;
   
6. 
   Hyparrhenia collina: perennial grass; good forage, but it should be stocked in the early stages of growth.
   
7. 
   Cynodon dactylon
   

Figure 6.3. Land cover in the Lower Nzoia block.

Table 6.4. Land cover classification

Vegetation strata	No. points	Percentage
Farm land	69	43.4
Forage land	16	10.1
Perennial grassland	40	25.2
Fallow	20	12.6
Other	14	8.8

Twenty percent or less of the land in clusters 3, 4, 6, and 7 were allocated to farming. A classification of the primary current land use showed the following:

Trees are not very common in the landscape. Out of the 640 sub plots sampled, we found 166 trees. No woodlots or planted plantations were sampled in the survey, but we did find several orchards with Mangoes and citrus species. Of the 160 plots sampled, 41% or 66 plots had trees in the vicinity. This woody vegetation is mostly broadleaf and evergreen, (Table 6.4).

The woody vegetation present in this area is needle leaf and evergreen. Markhamia lutea was the tree most commonly encountered. Acacia brevispica and A. hockii, Albizia coriaria and Cassia siamea were all fairly common as well. There were a few cypress plantations in the central portions of the block, but these were not picked up in our sample. Shrubs were widely present in the landscape and were measured on 90% of the plots. Few exotics were found on the plots sampled. Ipomea spp. was found in several sites in this block indicating low soil fertility.
Table 6.4. Wood vegetation type

Broadleaf	Needle leaf	Allophytic	Evergreen	Deciduous
78.1	0.0	15.0	63.1	8.8

In this block all farms surveyed are privately owned and for 24% of the plots were known to have a change in land use since 1990, while 28% of the plots were known to be in the same land use since that time. However, for the other 48% of the plots, it was impossible to ascertain whether land use has changed or not. Thus ther appears to be a moderate level of on-going land-use change in this area.

4. Soil erosion and conservation measures

Soil erosion was visible in 36% of the plots, with highest incidence in clusters 4, 13 and 16. Clusters 1, 2, 7, and 12 had the lowest incidence of soil erosion. The principal type of erosion is sheet erosion, but rill erosion in clusters 9 and 14 merit special attention by the project. . Table 3.56.5 indicates on a cluster basis, the percentage of points showing visible signs of erosion.
Soil and water conservation is not widely practiced in this block, but needs to be expanded. We found conservation structures present on only 10 plots, and most were in clusters 5 and 14. The clusters with the highest incidence of erosion were not the areas where most of the erosion control structures were encountered. Therefore, the project needs to begin creating awareness of the problem and then build on this awareness to help farmers begin to deal with the problem. Soil and water conservation practices in association with tree planting should be one of the first activities undertaken in this block.
Table 6.5. Percent of plots showing erosion features for each cluster

Cluster	None	Sheet	Rill
1	80	20	0
2	100	0	0
3	50	40	10
4	40	50	0
5	50	40	10
6	70	30	0
7	100	0	0
8	70	30	0
9	40	30	30
10	70	30	0
11	70	30	0
12	90	10	0
13	40	60	0
14	50	30	20
15	70	30	0
16	30	60	10