Combined Effects of Tillage, Mulching and Nitrogen Fertilizer Application on Maize Yields and Soil Properties in Tharaka-Nithi County, Kenya
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Date
2018-09
Authors
Abdi, Zeila Dubow
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
High dependence on rain-fed agriculture, low and erratic rainfall, inadequate water
and soil conservation techniques and declining soil fertility expose resource-poor
farmers to low agricultural productivity in tropical regions. A study was conducted
in 2012 at Kirege Primary School in Tharaka Nithi County to evaluate the effects
of soil tillage, soil surface management and nitrogen fertilisation on rain-fed maize
yields and properties of Humic Nitisols. Eight treatment combinations (T1M0N1,
T1M0N0, T1M1N1, T1M1N0, T0M0N1, T0M0N0, T0M1N1 and T0M1N0) were
laid out in randomised complete block design and replicated thrice. Data on grain
and stover yields, mineral N, soil water content and soil organic carbon content
were collected over six cropping seasons. Physical fractions of soil organic matter
were evaluated down to 0-80 cm depths. T1M1N1 and T1M0N1 treatment
combinations significantly had the highest maize yields in three out of six seasons
(SR2013, LR2014 and SR2014), ranging from a low of 1.9 Mg ha-1 in SR2013 to
a high of 4.9 Mg ha-1 in LR2015. T1M1N1 combination was superior for stover
yields in four out of six seasons, ranging from a low of 2.7 Mg ha-1 in SR2013 to
a high of 7.9 Mg ha-1 in LR2015. T0M0N1 combination had highest water use
efficiency for biomass production (WUEB), with the highest water use efficiencies
noted in LR2014 at 13.3 kg ha-1 mm-1 and short rains 2014 at 9.6 kg ha-1 mm-1
.Significantly higher WUEGY of 9.6 kg ha-1 mm-1 were recorded in T0M0N1 in
short rains 2014 and 3.4 kg ha-1 mm-1 in T1M0N1 in long rains 2015. Generally,
the NO3-N concentrations in all treatments decreased with increase in soil depth
from 0-20 and 20-40, after which the concentrations increased from 40-60 and 60-
80 cm depths. There were significant differences in the amount and distribution of
soil nitrate-N at the depths of 60-80 cm at 10 WAP, with higher net N
mineralisation in minimum tillage treatments than in conventional tillage
treatments. The highest soil water content in the study conserved in the minimum
tillage with mulch retained at 0 kg of N fertiliser while minimum tillage treatments
had higher crop evapotranspiration. Overall, soil carbon content decreased with
increase in soil depth. In all the three class size aggregates, the highest increases
in soil carbon were noted in the 0-20 cm depths, with the highest overall increases
in both soil meso-aggregates and macro-aggregates between 2012 and 2015
observed in T1M1N1 combination. There was enhanced soil carbon in the 0-20
cm depth in all the three aggregate fractions in treatments with conventional tillage
combinations, with increases of 3.5 t C ha-1 in micro-aggregates, 2.2 t C ha-1 in
meso-aggregates and 3.7 t C ha-1 in macro-aggregates. While more rains fall
during the SR seasons, the LR seasons were found to be more important, with
higher grain and stover yields in SR than LR. Retention of mulch on-farm was
found to be crucial for soil water conservation at soil depths below 50 cm and
enhancing mineralisation of nitrogen, showing a clear potential for seasonal water
buffering. This underscores the possibility of adapting to erratic climate regimes.
This research has confirmed the importance of conventional tillage practices in
ensuring better maize yields for farmers and promoting soil C content in
smallholder maize-based farming systems conducted in Humic Nitisols and that
in the long-term the formation of stable micro-aggregates in smallholder farms can
be useful carbon sinks.
Description
A Thesis Submitted in Fulfillment of the Requirements for the Award of the Degree of Doctor of Philosophy in Integrated Soil Fertility Management in the School of Agriculture and Enterprise Development of Kenyatta University, September 2018