The sustainability of maize production in western Ethiopia is in question despite of
favorable environmental conditions. A major reason for this phenomenon is severe soil
degradation in maize fields. This soil degradation manifested often in low soil N fertility
which inhibited maize yields. The situation is worsened by the financial inability of most
farmers to purchase N fertilizer for supplementation.
In these conditions two basic approaches can be followed to improve maize productivity in a
sustainable way. Firstly, integrated cropping practices can be developed for maize to make
better use of N from organic and inorganic sources. Secondly, maize genotypes can be
selected that are superior in the utilization of available N, either due to enhanced uptake
efficiency or because of more efficient use of the absorbed N. In this context, experiments
were conducted to determine the integrated effects of tillage system, residue management
and N fertilization on the productivity of maize, and to evaluate different maize genotypes
for N uptake and use efficiency.
The experiments on integrated cropping practices were done from 2000 to 2004 at five sites
viz. Bako, Shoboka, Tibe, Ijaji and Gudar in western Ethiopia. They were laid out in a
randomized complete block design with three replications. Three tillage systems (MTRR =
minimum tillage with residue retention, MTRV = minimum tillage with residue removal and
CT = conventional tillage) and three N levels (the recommended rate and 25% less and 25%
more than this rate) were combined in factorial arrangement. Every year yield response,
usage of applied N and changes of some soil properties were measured. In 2004 the same
experiments were used to monitor the fate of applied N in the soil-crop system. Labeled urea
was applied at the recommended rate to micro plots within the MTRR and CT plots for this
purpose. During the initial two years of the experiments, there was no significant difference in grain
yield between MTRR and MTRV and both were significantly superior to CT. However,
during the final two years of the experiments, there was no significant difference between
MTRV and CT and both were significantly inferior to MTRR. On average, the grain yield of
MTRR was 400 and 705 kg ha-1 higher than that of MTRV and CT, resulting in consequent
increases of 6.6 and 12.2%, respectively. The application of N increased the grain yield
regardless of tillage system. An application of 92 kg N ha-1 was significantly superior to 69
kg N ha-1, but on par with the 115 kg N ha-1 application. Hence, the recommended
fertilization rate of 92 kg N ha-1 for conventional tilled maize was also found adequate for
minimum tilled maize in western Ethiopia. This rate remained economically optimum with a
20% decrease in the maize price and a 20% increase in fertilizer cost.
The grain differences resulted from the tillage systems and concomitant residue management
were attributed to significant changes in some soil fertility parameters, especially in the
0-7.5 cm layer. After five years both indices of organic matter, viz. the organic C and total N
contents were significantly higher in the MTRR soils when the CT soils serve as reference.
Similarly, the extractable P and exchangeable K contents of the MTRR soils were also
higher than that of the CT soils. The only negative aspect of MTRR in comparison with CT
was a decline in soil pH.
A significantly higher grain N content was recorded with MTRR than with MTRV and CT.
The stover N content was not significantly affected by the three tillage systems. However,
grain, stover and total N uptake were consistently superior with MTRR compared to MTRV
and CT. The NAE, NRE and NPE of maize for the same tillage system were consistently
higher at the lower N level range of 69-92 kg ha-1 than at the higher N level range of 92-115
kg ha-1. At the lower N level range NAE and NRE were larger with CT than with the other
two tillage systems. Both indices were higher with MTRR than with the other two tillage
systems at the higher N level range. The NPE was not significantly affected by the tillage
systems. However, the trend at both N level ranges was higher with MTRR than with
MTRV and CT. The labeled urea study showed that the grain, stover and total biomass N derived from
fertilizer was consistently higher for CT than MTRR. Conversely, grain, stover and total
biomass N derived from soil was consistently higher with MTRR than CT. Therefore, the
fertilizer N recorded in the MTRR soils was higher with MTRR than CT and mainly
confined to the upper 45 cm. The fate of fertilizer N was in MTRR: 47% recovered by
maize, 17% remained in the soil and 36% unaccounted for and in CT: 54% recovered by
maize, 12% remained in the soil and 34% unaccounted for.
The experiments on genotype comparison for N uptake and use efficiency were also done at
Bako, Shoboka, Tibe, Ijaji and Gudar. In 2004 the response of five open-pollinated and five
hybrid genotypes were evaluated at six N levels from 0 to 230 kg ha-1 with 46 kg ha-1
intervals.
Only two out of the ten genotypes evaluated qualify as N use efficient. They were the openpollinated
Ecaval 1 and the hybrid CML373/CML202/CML384. These two CIMMYT
genotypes showed consistently higher NAE, NRE and NPE at low and high N applications
as required. This was not the case with the two local genotypes that were included, viz. the
open-pollinated Kulani and the hybrid BH 540. Based on the results that evolved from this study it is clear that:
1. Farmers should be encouraged to practice MTRR instead of CT since this change in
tillage system could improve the productivity of maize on Nitisols in western Ethiopia.
2. On these Nitisols the conversion from CT to MTRR need not coincide with an adaptation
in the recommended fertilization rate of 92 kg N ha-1.
3. The planting of N use efficient maize genotypes on Nitisols must be advocated to farmers,
especially those who can not afford proper fertilization. Aspects that need to be investigated in future are:
1. Quantification of N mineralization and immobilization in the Nitisols when subject to
MTRR and CT for maize production.
2. Losses of fertilizer N through volatilization, leaching and denitrification from the Nitisols
when subject to MTRR and CT for maize production.
3. Suitability of other soil types which are used for maize production in western Ethiopia for
MTRR instead of CT.
4. Performance of the N use efficient genotypes on other soil types which are used for maize
production in western Ethiopia.
5. Crop rotation with N fixing crops.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07302007-145850 |
| Date | 30 July 2007 |
| Creators | Dilallessa, Tolessa Debele |
| Contributors | Dr GM Ceronio, Prof CC du Preez |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07302007-145850/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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