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

INTRODUCTION

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.

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

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

MATERIALS & METHODES

Location of study area

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)

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

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

Methods (Cnt’d) Statistical analysis using GENSTAT package

RESULTS & DISCUSSION

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

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

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

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.

Effects of green manures on maize yields

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.

CONCLUSION & RECOMMENDATION

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

Murakoze Thank you Asante Sana Merci