Soil sampling was done by randomly auguring three auger holes within each plot and extracting soils at different depths of 0 - 15 cm, 15 - 30 and 30 - 45 cm from each auger hole. The three samples from each depth were mixed to form composite to give three samples from each plot. Soil sampling was done at three different seasons (December - March (warm dry), April - August (cool wet) and September - November (warm wet)). These samples were analyzed for pH before drying. The air-dried samples were crushed and sieved through 2 mm mesh for soil physical analysis and through 60 mm mesh for chemical analysis. The rainfall and temperature data for each sampling season was captured.

The disturbed soil samples were saturated in water tray with a constant depth of 10mm for 12 hours after which saturation mass was determined as per Klute method [10]. Samples were then transferred to a moisture extractor (soil moisture equipment Corp. USA) for moisture retention determination at 1 bar and 15 bars, respectively [10]. Soil available water content was calculated using the following:

AWC = FC − PWP

where FC is the water available content at field capacity and ɵPWP is the water content at permanent wilting point.

Soil texture and porosity were determined as per Klute [10], using the disturbed soil sample. Bulk density was carried out using core ring method and following laid down procedure on sampling and analysis. Organic matter analysis was carried out using 30% hydrogen peroxide chemical for decomposition. Dried 10 g soil sample was weighed and 50 ml of distilled water added. Floating particles removed followed by addition of 5 ml of 30% hydrogen peroxide on boiling until frothing ceased. The content was dried in the oven at 105˚C until constant weight was obtained. Organic matter was calculated as the difference between initial sample weight and final dry weight.

Soil pH was determined using a glass electrode pH meter at a ratio of 1:2.5 soils to water. Total N was done by weighing 1 g of soil sample into digester tubes followed by addition of about 1mls Sulphuric acid then put in Kjeldahl digester for 4 hrs. After digestion, the samples are run in Vapodest machine for distillation and titration [11]. Nutrient elements P, K, Mg, Ca, and Mn were determined following TRFK soil chemical analysis manual and subjected to Inductive Couple Plasma Emission (ICPE)-Shimadzu (9000 series) for individual element levels determination.

Tea was plucked at 7 - 10 days interval and their weight recorded per plot at every plucking round and seasons. The obtained yields were converted to Kg made tea per hectare per year using the formula n = (a × 0.225)/b. where n is the green leaf yield per plot, a is plant population per hectare while 0.225 is the factor converting green leaf to made tea [6] and b is the number of plants per plot prior to statistical analysis.

Data from tea soils were analyzed by ANOVA using SAS and GenStat software packages. Differences within the soil physical properties means were compared using Duncan’s multiple tests while the soil chemical properties means were compared using (Least Significant Difference) test at a significance level of 5% (p = 0.05).

1) Soil water availability

There were significant differences (p < 0.05) between the treatments in the first 2 seasons as shown in Table 3. Treatment SM gave the highest soil available water followed by enriched manure ratio 4:1 while NPK recorded the lowest (5.0% and 7.3%). This result suggests that enriched and organic manure improve soil water retention hence improve crop production. Similar findings were found by [13] that organic manure improves soil physical properties. NPK used gave the lowest soil available water to exhibit its negative effect on soil physical properties hence decreased soil water holding capacity. Related findings were reported by [14] on inorganic fertilizers study that high rates predispose tea plants to moisture stress through water inhibition and coupled with drought results may cause 14% - 20% tea yields reduction and 6% - 19% mortality rate [4]. Season 3 (WW) was not significant and had low soil available water compared to WD and CW seasons which might be due to high bulk density as a result of high rainfall (Figure 2). Though sheep manure improves soil physical properties, wet soil couple with tea plucking practices could have resulted in soil compaction which hinders water infiltration hence low soil water available.

Means followed by different letters down the column indicate significant differences at p < 0.05 by least significant difference.

The results in Figure 2 showed significant (p < 0.05) differences on soil available water with sampling depth used. There was slightly decreased in soil available water with increased in sampling depth across the seasons under study with a sharp dropped in WD and CW seasons. This trend implies that sheep manure improves water infiltration and water holding capacity hence available water in the soil. Similar results were reported on research done on roots characteristics of tea and silver oak that soil available water decreased on topsoil because tea plants feeder roots are within 30 cm deep [15] [16] hence water uptake within this region resulting. This reduced might have resulted in water capillary action hence decreased available water down the soil profile (Figure 2). This trend was more on WD season. Similar results were found out by [17]. The results showed, explicit low amount of available water during WW season and high on WD. This may be due to increased soil compaction during tea harvesting hence reduced pore space and water infiltration into the soil profile.

2) Soil bulk density

There were no significant (p < 0.05) differences between the treatments on the bulk density in all the seasons under the study (Table 4). However, the obtained results are within the recommended bulk density limits (less than 1.6 g/cm³) for soil agriculture [18]. This might be due to enriched sheep manure used which have improve soil organic matter and soil porosity hence desired bulk density. Moreover, significant differences were observed among the three sampling depths with the bulk density increasing with increasing depth and WW season giving high density (Figure 3). This might be due to heavy rainfall during April- June and human movement on tea plucking resulting in soil compaction hence increased bulk density. This is related to earlier studies found by [14] though on inorganic fertilizer use study that human traffic on tea harvesting increased bulk density down the soil profile.

3) Soil porosity

There were no significant (p < 0.05) differences between the treatments on the soil porosity in all the three seasons of the study (Table 5). Similarly, soil porosity was not significantly (p ≤ 0.05) affected by depths though there was slight

decline with increased sampling depth increased (Figure 4). This might be due to compaction as a result of field operation. This result is similar to earlier studies [19] [20] that human traffic caused soil compaction resulting in reduction of soil pore space hence decreased in soil water holding capacity. Enriched sheep manure used increased soil porosity which might due to the improved soil structure and addition of soil organic matter. Similar results were reported by [21] that organic manure adds a high percentage of organic matter into the soil.

4) Effects of enriched sheep manure and fertilizers on soil organic matter

The organic matter was significantly influenced by the treatments during the first and second seasons (Table 6). There were no significant differences between the treatments in the organic matter during the third season. The highest organic matter content (0.81%) was recorded on enriched manure of ratio 8:1 at 60 Kg∙N/ha/yr rate. The lowest organic matter (0.33%) was recorded on SM treatment during the WD season. The organic matter reduced significantly with increasing sampling depth (Figure 5). This might be attributed to leaf litter fall on topsoil hence build up soil organic matter. Early studies reported the same findings [22]. Enriched sheep manure increased soil organic matter compared to sheep manure alone to show that organic matter accumulation is related to tea leaves shootings and falling. This is expected because sheep manure

Means followed by different letters down the column indicate significant differences at p < 0.05 by Duncan multiple range test.

supplied required nutrients for tea plants to produce vigorous leaves and on falling accumulates over time building on soil organic matter. Again sheep manure adds a high percentage of organic matter into the soil on application. Same was affirmed by [21].

Generally, organic manure was higher on enriched manure (combined sheep manure and NPK) application plots. This is in agreement with [21] [23] findings that combined application of NPK and organic manure (enriched) increased soil organic matter (SOM) than compound fertilizer (NPK) applied alone. Low organic matter in season two implies that during dry period soil condition and harsh climate favor increased rate of decomposition hence low organic matter in the soil. Similar results were found out by [24]. This condition results in N loss hence low tea yields.

Table 7 indicates that soil chemical properties were significantly (p ≤ 0.05) affected by the treatment applied. There was a positive increase in soil pH in the

*Means followed by different letters indicate significant differences at (p ≤ 0.05) by least significant difference.

treatments applied with sheep manure alone giving the highest value of 2.05 (5.77) followed by enriched ratio 4:1, 8:1, zero fertilizer used and the least NPK with 1.9 (4.7). This finding is supported by [21] [25] that organic manure has a tendency of increasing soil pH during oxidation process. High soil pH with organic manure may be due to organic anions complex the Al⁺³ ions that contribute to soil acidity.

Total N had no significant (p ≤ 0.05) difference on treatment used though there was an increase with the use of sheep manure alone and enriched fertilizer when compared with control. The highest recorded total N was 0.2% on sheep manure alone and enriched sheep manure (SM) at a ratio of 4:1 at rate 240 used while control was 0.18%. These results might be due to slow release of nutrients in organic manure and high absorption rate of N by tea plants for production hence reduction of N in the soil. Similar results were found out by [18] that tea uses high rates of N fertilizer for optimum production.

P was significantly (p ≤ 0.05) increased with the use of enriched manure when compared to control and inorganic fertilizer used. These results show that organic manure increased soil pH hence availability of P nutrients in soil. Low soil P due to NPKS might be due to P fix due to acidic soil making it unavailable. K, Ca, Mg and Mn showed significant difference with increased availability on solely used SM and enriched manure. NPK obtained the least of these trace elements (K, Ca and Mg) followed by control. This was expected because organic manures are rich in K content hence addition on mineralization producing acid humus that help in adsorption hence minimum leaching [25]. Decrease in soil K⁺ content in NPK used might be due to low cations exchange and high aluminum accumulation leading to replacement of K by NH⁺ because of same ionic radii. This result revealed that continuous use of NPK fertilizer in tea farms may result in deficiency of K nutrients hence enriched organic manure is necessary for tea sustainability. Reference [26] found out that organic manure is rich in micronutrients especially K.