The document summarizes a study on the contribution of conservation agriculture principles (minimum soil disturbance, mulching, and crop rotation) to crop yields in Zimbabwe. It found that conventional tillage led to higher maize yields than reduced tillage. Integrating all three conservation agriculture principles did not increase maize yields compared to individual principles. The results for cowpea yields were inconclusive after two study seasons.

1. Contribution of conservation
agriculture principles to crop
yield in semi-arid Zimbabwe
Justice Nyamangara, Esther N. Masvaya and
Ronald D. Tirivavi

2. Introduction
• The strong interaction between livestock and
cropping in some smallholder areas of most of
SSA implies that farmers have difficulties to
integrate all three principles of CA at
recommended standards.
• Residues are also fed to livestock during the dry
season and in some communities used as fuel
and for construction of dwellings.
• Again, the prevalence of communal grazing rights
after harvest make it impossible for farmers to
unilaterally decide to keep crop residues on their
fields.

3. …..introduction
• Although CA has been widely promoted in
southern and eastern Africa, smallholder
farmers have largely adopted minimum soil
disturbance but few have adopted soil surface
mulching and/or diversified crop rotations.
• It is necessary to determine the contribution
of each CA principle to crop productivity so
that farmers can anticipate the magnitude of
gain/loss in yield if they omit any principle.

4. ….introduction
• The research question to be addressed is:
What is the relative contribution of each CA
principle to crop yield?
• It was hypothesized that the integration of all
three CA principles significantly contributed
to improved crop yield.

5. Materials and methods
• The trial was set up on a sandy soil at Matopos
Research station, Zimbabwe, for two seasons,
2010/11 and 2011/12
• Test crops: Zea mays (L.) (maize- variety SC513)
and Vigna ungiuculata (cowpea - variety CBC 1).
• Trial laid out in a split plot design with tillage the
main plot factor at two levels (CONV and reduced
tillage - RIPPER) and residue retention as the
subplot.
• Treatments: sole cereal, maize-cowpea rotation
and cowpea-maize and replicated four times.

6. …materials and methods
• To imitate smallholder conditions no residues
were applied in the first season but were
retained after harvesting and applied at 0 and
3 t ha-1 for maize residues and 1.5 t ha-1 for
legume residues.
• Fertilizer was applied to both crops at 100 kg
ha-1 basal fertilizer (7%N: 6%P: 6%K) and 90 kg
ha-1 top dressing (34.5% N).
• Daily rainfall, and grain and stover yield data
was collected.

7. Results and discussion
Sep Oct Nov Dec Jan Feb Mar Apr May
Cumulativerainfall(mm)
0
100
200
300
400
500
600
700
800
900
2010/11
2011/12
Figure 1: Cumulative rainfall at Sandveld, Matopos Research Institute,
Zimbabwe for the 2010/11 and 2011/12 seasons.
The 2010/11 season was wetter than 2011/12 as such
yields for both maize and cowpea were lower in the
latter season (Figure 1).

8. ……results and discussion
Maize yields
• Tillage had a significant effect on maize grain
yields in both the 2010/11 and 2011/12
seasons (P<0.05) with CONV consistently
giving the highest yields compared with the
RIPPER
• The grain yields averaged 1.06 and 0.86 t ha-1
for RIPPER and 2.2 and 1.3 t ha-1 for CONV in
the 2010/11 and 2011/12 seasons
respectively

9. ….results and discussion
2010/11 2011/12
CONV RIPPER SED* CONV RIPPER SED
Tillage only 2218 1059 358.5 1675 811 125.6
Tillage+Mulch 1383 798 177.6
Tillage+Rotation 921 956 177.6
Tillage+Mulch+Rotation 1383 895 251.2
Table 1: Maize grain yields for the 2010/11 and 2011/12
seasons at Sandveld, Matopos Research Institute,
Zimbabwe.
*SED – standard error of the difference of the means

10. ….results and discussion
• There were no significant differences in maize
yield when mulch and or rotation was
combined with tillage in the RIPPER treatment
• Nyamangara et al. (2013) reported high yields
when all 3 principles were applied by farmers
than with the application of 1 or 2 principles.
• The same study showed negative effects of
mulching and rotation when no fertilizer was
applied and positive when fertilizer was
applied.

11. Nyamangara, J., Masvaya, E.N., Tirivavi, R., Nyengerai, K., 2013. Effect of hand-hoe based
conservation agriculture on soil fertility and maize yield in selected smallholder areas in
Zimbabwe. Soil and Tillage Research 126, 19-25.

12. Cowpea yields
• There were no significant differences in cowpea grain yields in both
seasons as affected by tillage type or the interaction between
tillage type and mulch in the 2011/12 season.
• Cowpea yields ranged from 0.78 – 1.6 t ha-1 in the 2010/11 season
and 0.28 – 1.10 t ha-1 in the 2011/12 season.
2010/11 2011/12
CONV RIPPER SED CONV RIPPER SED
Tillage only 1133 1182 116.2 1001 637 156.2
Tillage+Mulch 837 1034 220.9
Table 2: Cowpea grain yields for the 2010/11 and 2011/12 seasons at Sandveld,
Matopos Research Institute, Zimbabwe.

13. Conclusions
• After two seasons, maize yield for CONV
tillage were superior to RIPPER tillage
• Integrating all three CA principles did
not lead to increased maize grain yields.
• The results for cowpea grain yields were
inconclusive after two seasons.