1. EFFECTS OF Calliandra calothyrsus and Alnus acuminata GREEN MANURES IN MAIZE PRODUCTION IN THE HIGHLAND VOLCANIC SOILS OF RWANDA Didace HABAMENSHI ISAE BUSOGO, RWANDA 2ND WORLD CONGRESS OF AGROFORESTRY Nairobi, August 22 – 28th, 2009

2. INTRODUCTION

3. INTRODUCTION
volcanic soils found in the northwestern Rwanda are naturally fertile and good for cropping.
62.0% and 32.5 % of national Irish potato and maize are respectively produced
Low available phosphorus (P) because ofhigh allophanes
continuous depletion as a result of continuous cropping without addition of adequate inorganic fertilizer and manure.
Most farmers are aware of the severity of soil degradation and rely on organic manures (especially animal manure and compost from household waste) to improve soil fertility improvement.

4. Introduction (Cnt’d)
However, low supply of these manures and high cost of inorganic fertilizers limit their use by many farmers.
Agroforestry technologies are seen as alternative to compensate for insufficient OM & costly min. fertilizers

5. Introduction (Cnt’d)
However, there is a knowledge gap on the required amounts, methods, frequency and time of application relative to soil fertility and nutrient release from manures.
The study evaluated the potential of Calliandra calothyrsus and Alnus acuminata green manures as sources of N and P for soil improvement and maize production

6. MATERIALS & METHODES

7. Location of study area

8. Materials Calliandra calothyrsus green manure (0, 5, 10 t/ha DM)
Alnus acuminata green manure (0, 5, 10 t/ha DM)
Maize (Zea mays pool 8A variety)

9. Alnus
Calliandra
Calliandra and other AF trees on degraded land
Alnus intercropped with Irish Potato in Musanze

10. Methods
Design: Factorial Experiment in RCBD with 6 treatments (including 2 controls), 3 replicates
Split application of manures with equal amounts at maize planting and 4 wks later
Data collection:
Soil sampling before & after the trial and analysis for N, P, OM & pH
Measurement of maize yield

11. Methods (Cnt’d)
Statistical analysis using GENSTAT package

12. RESULTS & DISCUSSION

13. Soil characteristics of the study area before the experiment
Site
pH (H2O)
pH KCl N
(%)
P(mg/kg)
OM (%)
ISAR Farm
5.36
4.73
0.55
4.7
6.53
ISAE farm
5.73
5.08
0.45
40.3
5.35

14. Before cultivation, studied soils were:
moderately acidic, moderate in N and high in OM content before cultivation.
low in available P content
ISAR site had low available P (4.7 mg kg-1) Vs moderate P concentrations at ISAE farm

15. Effects of green manures on soil properties
Site
Treatment
Parameters
N (%)
P (mg/kg)
pH water
OM (%)
ISAE Farm
Control
0.38
60.0
5.42
5.4
DAP + Urea
0.43
80.0**
5.74
5.7
Calliandra (5t/ha)
0.46
54.7
5.78
5.6
Calliandra (10t/ha)
52.0
5.97
Alnus (5 t/ ha)
0.45
48.6
5.87
Alnus (10 t/ ha)
0.50
53.7
5.99
ISAR
0.52
4.8
5.52
6.1
Farm
0.59
78.8**
5.49
6.4
Calliandra (5 t/ ha)
0.56
5.32
6.0
Calliandra (10 t/ ha)
0.64
5.44
6.2
0.53
4.7
5.43

16. At the end of the experiment:
No effect of green manures on soil N, P, OM and pH status at both study sites.
This may be attributed to
(i) Low decomposition of the applied materials
(ii) high content in allophane of the study area.
The application of mineral fertilizers (DAP and urea) increased the level of soil available P at both sites significantly. Hence, high response of volcanic soils to P fertilizers.

17. Effects of green manures on maize yields

18. Maize grain yields were higher at ISAE site.
The applied green manures did not improve maize grain yields unlike the mineral fertilizers (DAP and urea).
This was mainly attributed to the low P content and lack of synchrony between nutrient release and maize nutrient needs.
These results suggest that the application of C. calothyrsus and A. acuminata green manures some weeks before planting may benefit the season growing crop.

19. CONCLUSION & RECOMMENDATION

20. Increasing depletion of volcanic soils of Rwanda due to overcultivation.
Low effects of C. calothyrsus and A. acuminata green manures on soil N, available P, OM contents and pH
Similarly, no effect of the applied manures on maize yields.
Based on the results, the direct application of applied manures is likely to benefit the subsequent crop rather than the first one. Therefore, advisable to incorporate studied green manures some weeks before sowing or compost them before application

21. Murakoze Thank you Asante Sana Merci