2 Materials and Methods

Site description and experimental layout

The research used an existing experiment which was started in 1990 at Tea Research Institute, Timbilil estate, Kericho Kenya. The site is situated at an altitude of 2178 m asl, latitude 0⁰ 22’ S and longitude 35⁰ 21’ E and was a virgin forest prior to the start of experiment. The experimental design was a split-plot completely randomized block design with four main treatments (as plant population density i.e. 26,896; 13,448; 8,975 and 6,730 plants/ha) and four sub-treatments (as rates of nitrogen i.e. 80, 160, 240 and 320 Kg ha^-1 year^-1 as NPKS 25:5:5:5) replicated three times.

Samples collection

Soil samples were taken from four depths in all plots.

Soil samples

Soil were sampled from the field using an auger. They are transferred to clear polythene bags and labelled. Soil samples are taken to the drying shade to dry. This is the removal of moisture in the soil before they are sieved. When the soil samples are dry, they are sieved through a 2mm sieve. This is to obtain smaller particles which increases the ease of extraction by providing large surface coming in contact with the extractant. Soil pH (Thomas, 1996), phosphorus (Kuo, 1996), exchangeable potassium (Helmke and Sparks, 1996), exchangeable calcium and magnesium (Suarez, 1996) and available trace elements (Fe, Cu, Zn, Mn) (Lindsay and Norvell, 1978).

3 Results and Discussion

Soil samples results

Effect of plant population density, nitrogen fertilizer rates and soil depths on soil phosphorus, potassium, calcium, magnesium, manganese, aluminium, copper, iron and zinc are presented in Figures 1 to 9.

From the Figure 1, there was significant difference in P with increase in depth (LSD_0.05=3.32). Spacing 4X4 exhibited the highest phosphorus content at the rate160 KgNha^-1yr^-1 and 320 KgNha^-1yr^-1 across the soil depths. This indicates that different ppd have different abilities to absorb nutrients from the soils and leaching of the elements occur when applied at a higher rate.

Figure 1 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil P

There were significant (p≤0 .05) differences in mean levels of K due to nitrogen fertilizer rates (LSD_0.05=12.07) and the four depths (LSD_0.05=10.10) (Figure 1). The reason of this situation, with the excess nitrogen fertilizers application to tea plantation, tea plant vegetation and potassium uptake from soil increases, as a result potassium deficiency occurs (Kacar, 1984; Ranganathan and Natesan, 1987). The significant difference with depths is because of the high rate of leaching.

There was a significant interaction between the calcium and different nitrogen fertilizer rates (LSD_0.05=40.56) and depth (LSD_0.05=29.45) (Figure 2) meaning that the responses did not occur in the same pattern.

Figure 2 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil K

There was significant difference in magnesium with both nitrogen fertilizer rates (LSD_0.05=5.10) and depth (_LSD0.05=3.18) (Figure 3). Plant spacing 2X2 had the highest amount of magnesium across all depths (Figure 4).

Figure 3 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil calcium

Figure 4 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil magnesium

From the Figure 5, there is significant difference in manganese with depth (LSD_0.05=15.95). The amount of manganese is approximately the same in every depth at the rates of 160 KgNha^-1yr^-1.

Figure 5 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil manganese

The Figure 6 shows that there was significant difference in aluminium with depth (LSD0.05=40.87). The amount of aluminium decreases with increase in depth at fertilizer rates of 320 KgNha-1yr-1. Aluminium content in spacing 2X4 and 3X4 is approximately the same when fertilizer is applied at the rate of 160 KgNha^-1yr-¹.

Figure 6 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil aluminium

The mean levels of Cu varied with nitrogen rates (Figure 7) due to varied level of Cu supply to the soil.

Figure 7 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil copper

Significant (p≤0.05) differences were observed in Fe levels with depth (LSD_0.05=5.90) (Figure 8). There was increase in iron content in every depth with increase in fertilizer rates. This is due to the leaching of the soil content including iron.

Figure 8 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil iron

The mean levels of Zn varied from spacing to spacing (Figure 9) meaning that they have varied abilities to absorb Zn from the soil.

Figure 9 Effect of plant population, nitrogen fertilizer application rates and soil depth on soil zinc

4 Conclusion

The results showed that there were significant difference in many of the elements with population density and nitrogen fertilizer rates (LSD<0.05%). The significant difference with depths was majorly due to the high rate of leaching.

Acknowledgements

The authors are very grateful to Kenya Agricultural and Livestock Research Organization (KALRO), Tea Research Institute for fully funding the research.

References

Den Braber K., Sato D., and Lee E., 2011, Farm and forestry production and marketing profile for tea (Camellia sinensis), Specialty Crops for Pacific Island Agroforestry, Permanent Agriculture Resources, Hawai, pp.1-33

Eyupoglu F., 1999, Nutritional Status of Turkish Soils, Soil and Fertilizer Research Institute, Ankara, pp.112

Helmke, P.A. and Sparks D.L., 1996, Lithium, Sodium, Potassium, Rubidium and Cesium, In: Methods of Soil Analysis Part 3: Chemical Methods, Sparks D.L. (Eds.), Soil Science Society of America, Madison, WI, USA, pp.551-574

Kigalu J. M., 2007a, Effects of planting density and drought on the productivity of tea clones (Camellia sinensis L.): Yield responses, Phys. Chem. Earth., 32: 1098-1106.

http://dx.doi.org/10.1016/j.pce.2007.07.022

Kigalu J. M., 2007b, Effects of planting density on the productivity and water use of tea (Camellia sinensis L.) clones, Measurement of water use in young tea using sap flow meters with a stem heat balance method, Agric. Water Manage, 90: 224-232

http://dx.doi.org/10.1016/j.agwat.2007.03.005

Kigalu J. M., and Carr M. K. V., 2006, Effects of planting density and drought on the productivity of tea (Camellia sinensis L.) clones: Yield responses. WaterNet/WARFSA/GWP-SA Symposium

Kuo S., 1996, Phosphorus in Method of Soil Analysis, Part 3-Chemical Methods, Sparks, D.L., Page A.L., Helmke P.A., Loeppert R.H. and Soltanpour P.N. et al. (Eds.). SSSA-ASA Inc., Madison, WI., pp. 869-919

Lindsay W.L. and Norvell W.A., 1978, Development of a DTPA soil test for zinc, iron, manganese and copper. Soil Sci. Soc. Am. J., 42: 421-428.

http://dx.doi.org/10.2136/sssaj1978.03615995004200030009x

Nath T.N., 2013, The Status of Micronutrients (Mn, Fe, Cu, Zn) in Tea Plantations in Dibrugarh district of Assam, India. International Research Journal of Environment Sciences, 2(6): 25-30

Omwoyo W. N., Owuor P. O., Ongeri D. M., and Kamau D. M., 2014, Effect of Genotypes in Different Environments on Micronutrient Content of Black Tea, Journal of Tea Science Research, 4(2): 17-26

Owour, P.O., and Cheruiyot, D.K.A., 2011, Effect of nitrogenous fertilizer on major elements contents of mature tea leaf and extractable elements in soil.

Owour, P.O., Obanda, M., and Wanyoko, J.K., 1995, Quality response of low yielding tea to the rates and splitting nitrogen fertilizer application in the eastern and western Kenya highlands Tea, 16: 124-128

Owour, P.O., Wanyoko, J. K., and Rutto, J. K., 1995, Effect of plant population and nitrogen fertilizer on yield and quantity of clonal tea. Proceedings of 1995 International quality, Human Health Symposium, China, pp.324-332

Suarez, D.L., 1996, Beryllium, Magnesium, Calcium, Strontium and Barium. In: Methods of Soil Analysis: Chemical Methods, Sparks, D.L. (Ed.). Part 3, Soil Science Society of America, Madison, WI., pp.575-603

Wanyoko, J.K., Othieno, C.O., Mwakha, E., and Cheruiyot, D.K., 1997. Effect of types and rates of nitrogen fertilizer on leaf nutrients contents of seedling tea in Nandi Hills, Kenya. Tea., 18(1): 21-31