POTENTIAL OF CASUARINA EQUISETIFOLIA AND MELIA VOLKENSII TREE SPECIES IN IMPROVING SOIL FERTILITY IN KWALE AND KILIFI COUNTIES, KENYA

Abstract

Low soil fertility is a major biophysical root-cause of declining per capita land productivity in Kenya. In most parts of the country, soils are deficient in nitrogen, phosphorus and in some cases potassium. Trees are important in soil fertility enhancement as they offer an excellent opportunity for farmers to meet nutrient demand in agricultural systems. The aim of the study was to determine the potential of Casuarina equisetifolia and Melia volkensii tree species on soil fertility improvement in Kwale and Kilifi Counties, Kenya. The experiment was established on-farm in a randomized complete block design (RCBD) with three treatments: Casuarina, Melia and control with eight replicates arranged in 20 x 20 m tree plots. Soil samples were obtained in 2013, 2014, 2015 and 2016 from depths of 0 to 20 cm, 20 to 40 cm and 40 to 60 cm and analyzed for soil pH, Electro Conductivity; soil Carbon (C), total nitrogen (N), available phosphorus (P) and Potassium (K), Data was subjected to Analysis of Variance using R version 4.0.2 for windows. Results indicated that total N and P were higher in C. equisetifolia and M. volkensii plots compared to the control treatment; and total Carbon was higher in M. volkensii treatment. There was a gradual decline soil C across the assessment period which could be attributed to higher decomposition rates at the study sites. There was also a positive relationship between soil pH and soil P (r2

=0.128, 0.345, 0.327 for 2014, 2015 and 2016 respectively). The results indicated that C. equisetifolia and M. volkensii slightly enhanced soil fertility through increased N and P, which can be attributed to nitrogen fixation by C. equisetifolia through Frankia bacteria and nutrient recycling by M. volkensii.