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
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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.