EFFECTS OF LEGUME COVER CROPS ON SOIL PROPERTIES AND PRODUCTIVITY OF GRAFTED ORANGES (Citrus sinensis) IN THE COASTAL LOWLANDS OF KENYA

Abstract

Orange (Citrus sinensis) is an important food and cash crop in coastal lowland of Kenya. The average orange production in Kenya is 12 tones/ha Compared to world production of 16 tones/ha due to low soil fertility, diseases and high costs of inputs. There is, therefore, a need to develop a sustainable and low input production system for increased orange productivity and improved fruit quality in coastal lowland of Kenya. This study was tconducted at KALRO-Matuga, Ganda and Vitengeni within the coastal region of Kenya from May 2012 to April 2015. The effects of legume cover crops on soil moisture, orange feeder root distribution, soil pH, plant nutrients, orange yield and fruit quality was evaluated. There were four treatments; mucuna (Mucuna pruriens), cowpea (Vigna unguiculata), dolichos (Lablab purpureus) cover crops and a fallow as the control. The experiment was laidout in a randomized complete block design (RCBD) where the treatments were replicated four times within four blocks in an existing grafted Valencia orange orchard. Soil and orange root sampling was between 2m and 3m radius from the orange trees trunk at two depths topsoil (0-20 cm) and sub-soil (20-40 cm). Fruit and leaf samples were taken from the orange trees. Data collected was subjected to analysis of variance (ANOVA) at (P ≤ 0.05) using procedures of R statistical analysis version 3.3.2. Mean separation was done using the least significant difference (LSD) at (P ≤ 0.05) level of significance. Mucuna, dolichos and cowpea increased soil moisture content in orange orchard for all the site topsoil while in the sub-soil is only mucuna and dolichos increased moisture content in the soil. Mucuna and dolichos increased orange root density in the top and sub-soils. Mucuna, cowpea and dolichos increased soil nitrogen in the orange orchard top and sub-soil. Mucuna, cowpea and dolichos increased soil organic carbon in the orange orchard top and sub-soil. Mucuna increased phosphorous in the top and sub-soil of orange orchard. Dolichos increased phosphorous in the topsoil of orange orchard.. Cowpea and dolichos increased phosphorous in the sub-soil of orange orchard. Mucuna, dolichos and cowpea increased the potassium in xxii the topsoil of orange orchard while in the sub-soil, potassium increase due to mucuna and cowpea. Mucuna dolichos and cowpea increased orange leaf chlorophyll content. The orange fruit number increased due to mucuna and dolichos. Orange fruit weight increased due to mucuna and dolichos. Fruits size increased due to mucuna and dolichos. Fruits juice increased due to mucuna and dolichos. Orange fruit brix increased due to mucuna and dolichos. In conclusion, mucuna, dolichos and cowpea are effective in improving soil moisture, root distribution and nutrients in the soil and orange yield and fruit quality. The use of mucuna however, had the highest increase and it is strongly recommended as a cover crop in orange production. Further research is however recommended to evaluate the long term (>3years) effect of the cover crops under different Agro-ecological zones.