Assessment of the Mineral Elements in the Soil of a Bixa Field and their Distribution in various Plant Tissues on Application of Organic and Inorganic Fertilizer Amendments

Abstract

Bixa orellana L. is a shrub that is commercially known as ‘annato’. Its main product is organic dye, which is present in the seed coat, commercially called ‘annatto’. It is widely used in the cosmetic and the food industry for giving red to orange-yellow colours to foodstuffs and cosmetic products. Bixa farming in Kenya has declined since the 1970’s due to the use of cheap synthetic materials as food and cosmetic colours, which have proved to be carcinogenic. This has triggered a high demand for natural colours from bixa. However, the quality of bixa remains low due to suboptimal application of fertilizers. The objective of this study was to determine the mineral elements in the soil and their distribution in tissues of bixa plants treated with organic and inorganic fertilizer amendments for increased bixa quality. A study was undertaken at the Bixa Company farm at Shimoni in Kwale County in 2018 and 2019. Bixa plants of the same age were applied with different levels of organic (poultry manure at 5 tons/ha and 10 tons/ha) and inorganic fertilizers (NPK 17:17:17 at 100 kg/ha and 150 kg/ha) and a combination of the two (2.5 tons/ha plus 50kgs/ha NPK and 5 tons/ha plus 75kgs/ha NPK) with a control in a randomized complete block design with three replications. Bixa roots, stems and leaves were analyzed for the distribution of both macro and micro nutrients. The data obtained was subjected to ANOVA using SAS version 8.2. Significant means were separated using LSD at α = 0.05. The study revealed that application of manure at the rate of 10t/ha and NPK at the rates of 100kg/ha and 150kg/ha significantly (p < 0.05)  improved soil fertility and nutrient levels in the various plant tissues compared to the other treatment combinations. More nutrients were found in the leaves followed by stems and then the roots. At the same time the quality of the bixa produced was higher in the three treatments than the rest.