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Plant material, treatment structure and cultural practices
Three East African highland banana cultivars, including two cooking cultivars (“Ingaju” and “Injagi”) and one beer cultivar (“Intuntu”), were used in this study. Plants were established from young (< 1.0 m height), healthy sword suckers. All suckers originated from farmers’ fields near the Kibungo site. Corms were pared to remove any lesioned tissue and were subsequently subjected to hot water treatment at 50-55°C for 20-25 minutes (Sarah et al., 1996; Speijer et al., 2000; Elsen et al., 2004; Hauser, 2007) to reduce nematode infestation in the plant and improve sucker establishment and survival. Trials were established in April 2007 at Kibungo and Rubona, and in November 2007 at Ruhengeri. The experimental designwas a randomized complete block with five densities (plants ha-1): 1428 at a spacing of 3.5 m × 2.0 m, 2500 at 2.0 m × 2.0 m, 3333 at 1.5 m × 2.0 m, 4444 at 1.5 m × 1.5 m and 5000 at 1.0 m x 2.0 m. There were three replicates per site. Plots were 14 m × 12 m and planting pits were 45 × 45 × 45 cm in size. A basal dressing of 6 kg dry cattle manure was applied in each planting hole. Thereafter, neither external mulch, nor inorganic inputs were applied. A minimum sample of 15 plants surrounded by a border row was considered as the net plot for data collection for both growth and yield parameters (Nokoe & Ortiz, 1998). Throughout the trial period, desuckering was done to maintain a maximum of three plants per mat; i.e. one mother, one follower as first ratoon and one sucker as second ratoon. Weeded grass, old banana leaves and split pseudostems of harvested plants were left as self mulch in all treatments.
Measurements of vegetative growth characteristics
During the early stages of growth (i.e. up to nine months after planting), plant growth traits were measured at one month intervals. Thereafter, measurements were taken at two month intervals and terminated at the flowering stage. Pseudostem height and circumference at ground level and at 1 m were measured. Pseudostem volume was calculated using allometric relationships from Wairegi et al. (2009). At each interval-measurement, the number of functional (considered as > 50% green) and dead leaves were recorded, as well as the length and the width of the third middle leaf from the top. The total plant leaf area was then calculated following the methodology of Nyombi et al. (2009). Leaf area index (LAI) was computed for each density as the total leaf area per plant divided by the ground area available to each plant. LAI measurements were made from six months after planting to early flowering.
Measurement of yield parameters
At each harvest, the following data were recorded: date, bunch mass, number of hands per bunch, and number of fingers of the lower row of the second lowest hand. Total fresh mass of bunches, pseudostems, and leaves were measured using a field balance (± 0.5 kg). Fresh subsamples of fingers, pseudostems and leaves were oven-dried at 70°C for 72 h for dry matter determination. Total above ground dry matter yields (bunches + leaves + pseudostems) were expressed as t ha-1 cycle-1. The harvest index on a dry mass basis was computed as the bunch dry matter divided by total above ground dry matter and multiplied by 100 to express it as percentage. The total fresh yield in t ha-1 was calculated from the mean bunch mass and plant density. The yield per ha per year (t ha-1 yr-1) was then computed as [(yield per ha)/cycle duration in months] × 12 (Robinson & Nel, 1989; Kesavan et al., 2002). Cycle duration was from planting to harvest for plant crop, and between two successive harvests from the same mat for the ratoon crop. Due to wind damage at Rubona and the incidence of Bacterial Wilt Disease (caused by Xanthomonas vasicola pv. Musacearum, formerly Xanthomonas campestris pv. musacearum) at Ruhengeri, bunch mass and yields from the ratoon crop in both sites were estimated at pre-harvest stages using allometric relationships developed by Wairegi et al. (2009), a reliable non-destructive method to estimate bunch mass in the field.
Soil and plant analyses
Prior to experimental set up, composite soil samples from each plot were collected. Before flowering of the plant crop, soil subsamples were collected at 0-30 cm depth and composited for each plant density treatment. Soil samples were oven dried at 105°C for 48 hours, groundand sieved (< 2.0 mm). Soil pH was measured in 1:2.5 (sediment:water suspension) as described by Okalebo et al. (2003). Soil organic carbon content was determined using the Walkley-Black procedure (Nelson & Sommers, 1982). Total N was determined by Kjeldahl digestion and measured with spectrophotometry (Okalebo et al., 2003). Exchangeable cations (Ca, Mg and K) were extracted using a 1.0 M ammonium acetate solution, while for available P, Mehlich-3 solution (Mehlich, 1984) was used. Phosphorus was measured colourimetrically using the molybdenum blue method. Potassium was measured using a flame photometer, while the other cations were determined using an atomic absorption spectrophotometer.
Texture analysis was performed using the hydrometer method (Gee & Bauder, 1986). To analyse for nutrient mass fraction, foliar subsamples of 10 by 10 cm were collected from both sides of the midrib in the midpoint of the lamina from the third most fully expanded leaf of a flowering plant (Lahav, 1995) and composited for each density treatment. Foliage samples were oven dried at 72°C for 48-96 hours, ground, sieved to < 2 mm particle size, and digested in a sulphuric acid and selenium mixture (Okalebo et al., 2003). N and P were determined colourimetrically, while K, Ca and Mg were determined using the atomic absorption spectrophotometer.
CHAPTER 1 GENERAL INTRODUCTION
1.1 EAST AFRICAN HIGHLAND BANANAS (MUSA SPP.)
1.2 SOIL FERTILITY PROBLEMS IN THE EAST AFRICAN HIGHLAND REGION
1.3 CONSTRAINTS AND OPPORTUNITIES OF EAST AFRICAN HIGHLAND BANANA CROPPING SYSTEMS
1.4 PLANT DENSITY MANAGEMENT AS YIELD MAINTAINING FACTOR
1.5 RATIONALE OF THE STUDY
1.6 OBJECTIVES OF THE STUDY
CHAPTER 2 ECOLOGICAL CHARACTERISTICS INFLUENCE FARMER SELECTION OF ON FARM PLANT DENSITY AND BUNCH MASS OF LOW INPUT EAST AFRICAN HIGHLAND BANANA (MUSA SPP.) CROPPING SYSTEMS
ABSTRACT
2.1 INTRODUCTION
2.2 MATERIALS AND METHODS
2.2.1 Surveyed areas and methodology
2.2.2 Field measurements
2.2.2.1 Plant density
2.2.2.2 Estimation of bunch mass
2.2.3 Plant and soil nutrient status
2.2.4 Rainfall and evapotranspiration data .
2.2.5 Data exploration and statistical analyses
2.3 RESULTS
2.3.1 Plant density and bunch mass
2.3.2 Plant density, soil and plant nutrient contents and bunch mass relationships
2.3.3 Distribution of plant density and influence rainfall and altitude
2.3.4 Influence of intercropping on plant densities and bunch mass
2.4 DISCUSSION
2.4.1 Variations in plant density and their impact on bunch mass
2.4.2 Soil fertility, plant density and bunch mass relationships
2.4.3 Influence of cropping systems on plant density and bunch mass
2.5. CONCLUSIONS
CHAPTER 3 .COLOGICAL CHARACTERISTICS AND CULTIVAR INFLUENCE OPTIMAL PLANT DENSITY OF EAST AFRICAN HIGHLAND BANANAS (MUSA SPP. AAA-EA) IN LOW INPUT CROPPING SYSTEMS
ABSTRACT
3.1 INTRODUCTION
3.2 MATERIALS AND METHODS
3.2.1 Experimental sites
3.2.2 Plant material, treatment structure and cultural practices
3.2.3 Measurements of vegetative growth characteristics
3.2.4 Measurement of yield parameters
3.2.5 Soil and plant analyses
3.2.6 Climatic data .
3.2.7 Statistical analyses .
3.3 RESULTS
3.3.1 Yield components
3.3.1.1 Bunch yields and bunch mass
3.3.1.2 Total above ground dry matter yields and harvest index
3.3.2 Vegetative growth
3.3.2.1 Growth of the plant pseudo-system
3.3.2.2 Crop cycle
3.3.3 Optimal agronomic plant density
3.3.4 Resource availability for banana performance
3.3.4.1 Water availability
3.3.4.2 Soil and leaf nutrient contents
3.3.4.3 Leaf area index (LAI)
3.3.4.4 Growing degree days
3.4 DISCUSSION .
3.5 CONCLUSIONS
CHAPTER 4 NUTRIENT IMBALANCE AND YIELD LIMITING FACTORS OF LOW INPUT EAST AFRICAN HIGHLAND BANANA (MUSA SPP. AAA-EA) CROPPING SYSTEMS
ABSTRACT
4.1 INTRODUCTION
4.2 MATERIAL AND METHODS
4.3 RESULTS
4.4 DISCUSSION
4.5 CONCLUSIONS
CHAPTER 5 INFLUENCE OF PLANT DENSITY ON VARIABILITY OF SOIL FERTILITY AND NUTRIENT BUDGETS IN LOW INPUT EAST AFRICAN HIGHLAND BANANA (MUSA SPP. AAA-EA) CROPPING SYSTEMS
CHAPTER 6 GENERAL CONCLUSIONS AND RECOMMENDATIONS
