Abstract:
To attain agricultural sustainability, use of soil resources and
tillage requires equal consideration for chemical and physical
components of soil fertility. We assessed responses of selected soil
physical and chemical properties to tillage and soil fertility
amending resources. The study was carried out in Meru South and
Kandara sub-counties located in the Central Highlands of Kenya
for four cropping seasons. The experimental design was split-plot
with tillage as the main factor - conventional (D15) - and minimum
(D0) tillage and soil fertility resources (SFR) as sub-factors - mineral fertilizer (F), crop residues + fertilizer (RF), residues + fertilizer + animal manure (RFM), residues + Tithonia diversifolia +
manure (RTiM), residues + Tithonia diversifolia + phosphate rock
(Minjingu) (RTiP), residues + manure + legume intercrop (RML)
and control (no input). Compared with control, aggregate stability
was significantly higher on average under SFRs with sole organics
by 19% in Meru South. Total N and available P were higher under
integration of fertilizer and organics in both sites. Calcium
increased under sole organic or integration with fertilizer in Meru
South and under sole organics in Kandara. Magnesium significantly increased under all SFRs compared with control in
Kandara. Soil organic carbon significantly (P=0.02) increased
under D0 by 6% compared to D15 in 0-5 cm depth in Kandara.
Application of RTiM had the highest SOC in all depths’ at Meru
South. SOC significantly increased under RTiP and RML by 11%
in 0-5 cm depth and under RML by 13% in 5-10 cm depth at
Kandara. Mineral-N (NO3
–-N and NH4
+-N) was higher under D0 at
planting compared with D15 in Meru South. In Kandara, NO3
–-N
and NH4
+-N were significantly higher by 17% and 30%, respectively under D0 compared with D15 at planting during SR16 season. Higher mineral N was recorded under F application on the
30th and 45th days in both sites. The highest mineral-N content was
on the 45th day after planting during SR16 season and on the 30th
day during LR17 season at Meru South. In Kandara, NO3
–-N and
NH4
+-N were highest on the 45th day and 30th day, respectively,
during SR16 season. During LR17 season, mineral-N was highest
on the 30th day in Kandara. The study highlights that minimal soil
disturbance and organic inputs use or integration with fertilizers
are feasible alternatives for improving soil fertility in the Nitisols
of Central Highlands of Kenya.
