Effect of Legume Cover Crops on Soil Moisture and Orange Root Distribution

Citrus root system plays an important role in physical tree support and anchorage into the soil. They
also provide a mean of collection and transport of water and nutrients essential for tree growth and
production. Inadequate rain is a major hindrance to soil moisture and crop root growth in arid and
semi-arid areas of Kenya. A field study was conducted in Ganda, Vitengeni and Matuga locations
within the coastal lowland region of Kenya from May, 2012 to April, 2015 to evaluate the effects of
three leguminous cover crops on soil moisture retention and orange tree feeder root distribution.
Treatments included mucuna (Mucuna pruriens), cowpea (Vigna unguiculata), dolichos (Lablab
purpureus) cover crops and unplowed fallow of natural vegetation as a control. The experiment was
laid out in randomized complete block design (RCBD) and each treatment was replicated four times.
Data collected were: soil particle size distribution, soil moisture content and orange dry root density.
The data collected was subjected to analysis of variance (ANOVA) using procedures of R statistical
analysis version 3.3.2. Mean separation was done using the least significant difference (LSD) value at
5% level of significance. Results indicated that mucuna, dolichos and cowpea cover crops significantly
(P=.05) increased soil moisture content. The mucuna treated plots recorded an increase in SMC by
39.0% and 33%, dolichos increased by 34.4% and 28.9% and cowpea by 33.6% and 27.3% at soil
depth 0-20 and 20-40 cm, respectively, over their own controls. Mucuna and dolichos significantly
(P=.05) increased orange feeder root distribution. Mucuna treated plots supported the highest
increase in orange root distribution by 36.5% and 31.8%, dolichos increased by 30.2% and 34.1%
while cowpea increased by 18.3% and 18.8% in soil depth 0-20 and 20-40 cm respectively compared
to their own control. It can be concluded that the three legumes; mucuna, cowpea and dolichos cover
crop improved soil moisture retention and root distribution in orange production. The overall ranking
was as follows: mucuna > dolichos > cowpea. From the finding, the use of mucuna and dolichos cover
cropping system is recommended as a soil management practice aimed at improving the orange
productivity. Further evaluation on the long term (>3 years) effects of cover crops on soil moisture and
orange root distribution under different agro ecological zones is suggested.