Saw dust is one of the byproducts of saw milling, which is a major economic activity practiced in countries with large forests resources ( Leconte et al., 2009

Saw dust has also been used as a soil conditioner in general agriculture ( Garner, 2014 ). Saw dust is purely wood material comprising of 50% carbon ( Parry, 2007 ). Its incorporation into the soil enhances a buildup of soil organic carbon pool which is slow to decompose and which can act as agricultural strategy on climate change mitigation that reduces emission of greenhouse gases.

Most of our soils are greatly in need of organic matter because the usual crop rotations and degradation seldom maintain soil humus at desirable levels and thus saw dust can provide these nutrients over a long period if decomposition is managed appropriately. Saw dust is also a largely sterile media that does not harbor microorganisms due to its low nutrient content ( Okalebo et al., 2002 )

Decomposition is one of the most important processes that accounts for carbon and nutrient recycling on crop land and in the forest systems (Shi, 2013) . It is controlled by factors such carbon to nitrogen ratio (Richard & Trautmann, 2014) , pH and nutrient balance in the medium, particle size, temperature, moisture content and porosity (Bernal et al., 2009) . The slow rate of decomposition of saw dust and temporary depression of nitrogen has been the principal objection to its use in agricultural fields (Garner, 2014) . In addition, sawdust is low in readily available plant nutrients when compared to livestock manure which is rich in microbes responsible for rapid decomposition of organic matter and pH of 6.0 - 9.0 which is ideal for microbial activity (Pennington, 2009).

Livestock manure (cow dung) has low carbon to nitrogen ratio of 25 - 30 which is ideal for provision of required energy for microbial activity as well as a high water holding capacity. The high concentration of macro nutrients in cow dung provide initial nutrients required for the decomposition process. These factors make cow dung an ideal component for mixing with sawdust to enhance its decomposition and meet the immediate and long term plant nutrient requirements. Cow dung has been extensively used in crop production in Kenya and is often recommended as a soil nutrient replenishment strategy in low income countries (Okalebo et al., 2006). Forest soils are commonly used to raise seedlings in the nursery. The soils are collected from natural forests. For example in motanne forests in Kenya, forest soils are collected under Tombeya torrida. The soils may not contain all essential nutrients either due to leaching or utilization by under growth. Addition of small quantities of inorganic fertilizer is recommended as a supplement for good growth of seedlings in the nursery (Evans, 1983).

Seedlings height is one of growth parameters used to determine planting stage of seedlings in the field. Lamprecht (1989) recommended a height of 10 - 25 cm as most ideal for planting out Eucalyptus saligna in the field for better survival. However, Evans (1983) showed that height is not satisfactory for grading plants and recommended root collar diameter which is highly correlated with survival of the seedlings in the field.

There exists minimal knowledge on how sawdust can be utilized as a growth medium in forest seedlings establishment as well as the appropriate mixing ratios for enhanced decomposition. Thus, this study was aimed at mixing sawdust with cow dung and/or forest soil to form a nutrient rich growth media that can be used to raise quality and fast growing tree seedlings. Specifically, the study sought to find out how the growth media comprising sawdust, forest soil and/or cow dung affects growth characteristics of Blue gum (Eucalyptus saligna) seedlings raised in South Kinangop Forest Station of Kenya.

The study was carried out in South Kinangop forest station in the Aberdare Forest Reserve (Figure 1). The station is located on latitude S 00˚43'28.4", longitude E036˚40'51.7" and 2545 m elevation. The forest occupies a total 6660 hectares and forms part of the Aberdare range which is one of the major water towers serving Lake Naivasha to the north and Tana River to the south. The climate at South Kinangop is modified equatorial climate with average temperature of 12.3˚C and annual rainfall of about 1590 mm distributed bi-modally with peaks in late April and late November.

The field layout comprised of six treatments (Tr 1 - 6) in a completely randomized design with three (3) replications.

Forest soil was dug and collected from the natural forest stands of Dombeya torrida within South Kinangop forest. Fine sawdust mainly from pine (Pinus patula) trees was collected from nearby sawmill while cow dung was sourced from homesteads near the forest margins. The sawdust, forest soil and cow dung were heaped separately in the nursery and preparations for the growth media carried out during the dry period (August 2015). The treatment mixtures were allowed to decompose for three months under shade so as to improve on aeration, reduce instances of dumping off disease to seedlings, reduce competition of nutrients from weeds, and increase water retention capacity.

Eucalyptus saligna seeds were acquired from Kenya Forest Research Institute (KEFRI), Muguga Seed Centre and sown in a seed bed of sand, two weeks before the completion of decomposition period of the nursery growth media. After germination the seedlings were allowed to grow for 14 days in the seed bed and on the 15^th day after germination, the seedlings were pricked out into polythene tubes at one seedling per tube. In total three hundred and thirty (330) polythene tubes of size 3’’ by 4’’ were filled with the growth media for each of the treatment described in Table 1. A total of 1980 tubes were filled for the six treatments. The tubes were arranged in an experimental unit of 110 seedlings per replicate which were then completely randomized and replicated three times. The seedlings were allowed to grow for 6 months under open and uncontrolled climatic conditions. During the experimental period, temperatures ranged from 19.9˚C during the day to 3.2˚C at night with mean temperature being 12.3˚C. Humidity ranged from 100% during early hours of the day to 40% late in the afternoon and an average of 65%. Sunlight was controlled through shading after pricking out from week 1 up to week 2. Afterward the shade was removed to allow for total exposure of seedlings to sunlight.

Data collection involving height, root collar diameter and biomass sampling was