| dc.description.abstract | Nutrient mining through harvested products, without adequate replenishment, has reduced soil
nutrient stocks and maize yields in Kabete, Kenya. The use of inorganic fertilizers to replenish
soil fertility is expensive and beyond reach for many farmers. Minjingu rock phosphate (MPR)
use, under different legume-maize cropping systems, is a low cost and viable alternative that
could potentially improve maize productivity. MPR is cheaper than other fertilizers, has high
phosphate content and exhibits positive residual effects on crop yields. However, it has a slow
phosphorus release pattern. Legumes white lupin (Lupinus albus L. cv. Amiga) and chickpea
(Cicer arietinum L.), apart from fixing nitrogen (N), can enhance MPR solubility through
protonation, hence increase maize yields. The broad objective of this study was to contribute
towards enhanced soil fertility and maize yields through use of alternative low cost legume and
fertilizer based technologies. The study was conducted at Kabete Field Station of the University
of Nairobi in the long (LRS) and short rain seasons (SRS) of 2012. The experimental set up was
a randomized complete block design with a split plot arrangement. The main plots were three
cropping systems; maize monocrop, legume-maize rotation and legume/maize intercrop. The
split plots were two phosphorous sources: triple super phosphate (TSP) and MPR. Soil and plant
samples were collected at seedling, tasseling and maturity stages of maize growth and analyzed
for N and P nutrient levels. Soil pH was monitored across maize growth. Maize grain and dry
matter yields were measured at harvest. Soil N, P and K balances were determined at termination
of experiment using the NUTMON-Toolbox. Available P (mg kg-1) was highest in the rotation
systems involving chickpea (16.3) in the SRS and (10.1) in the LRS, implying an overall
increase. The highest soil available N (SAN) was recorded in chickpea-maize rotation systems
with TSP applied.
The pH of soil was highest in the maize monocrop (5.5) and lupin-maize rotation (6.0) with TSP
and MPR applied, for LRS and SRS respectively. Plant P was highest in chickpea/maize and
lupin/maize intercrops, and lupin-maize (L-M) rotations with MPR applied. This trend was
similarly observed for the plant N. Higher grain yields were recorded in MPR-treated compared
to the TSP-treated plots in both seasons. A general increase of grain yield (t ha-1) over the
seasons was noted i.e. LRS (3.03, 4.04 and 4.16) and SRS (3.78, 4.32 and 5.06) for the control,
TSP and MPR respectively. This trend was repeated in the dry matter yield (t ha-1) i.e. LRS
(5.01, 5.9 and 6.17) and SRS (5.84, 7.46 and 8.98).White lupin proved superior to chickpea at P
mobilization from MPR and availing N in soil. Soil N and P balances recorded were negative i.e.
16.2 and 21.5 kg P/ha/yr. K balances were positive in the C/M control and with TSP. Higher
balances were recorded where chickpea was used as either an intercrop or in rotation with maize.
The use of MPR as a source of P holds promise as it results in higher crop yields in legumemaize
cropping systems and is recommended for improved soil fertility in small holder farms.
Improved yield and soil N and P levels were obtained with inclusion of legumes and application
of MPR across seasons. In general, MPR was able to yield similar and/or better results for all
parameters under study hence recommended for adoption under legume-maize intercrop systems. | en_US |
