PhD thesis Abstract
The role and importance of livestock in smallholder crop-livestock systems and the importance of crop residues (CR) as ruminant feedstuffs in such systems are well established. The effects of genotype (G), environment (E) and crop management (M) factors on yields of grain and CR and the nutritive value of the CR of maize (Zea mays) and common bean (Phaseolus vulgaris) were investigated in an East African context. Genotype effects were examined in early and medium maturing (EM and MM, respectively) maize hybrids and popular varieties of common bean. Environment was examined at three sites for maize in the 2013 and 2014 cropping seasons and at four sites for common bean in 2013. Management effects examined were plant density (D) (5 and 7 plants/m2), height of cutting at harvest in maize, and harvest at early and final seed maturity in common bean. Quality attributes (nitrogen (N), neutral detergent fibre (NDF) and acid detergent fibre (ADF) contents and dry matter digestibility (DMD)) were analysed using near infrared spectroscopy (NIRS) and calibrations expanded and validated with reference samples of CR representing the experimental sample set.
There was substantial variation (P<0.05 to P<0.0001) among maize genotypes in yields of grain and stover and quality of stover as a feedstuff. Dual purpose genotypes were identified but G x E interactions for some yield and quality attributes showed that the variation among genotypes can depend on environment. In general the higher D increased yields of grain by 9-15% and stover by 21-31%, but had only minor effects on stover quality attributes. Year (Y) x density (D), G x E and G x D interactions were observed for some of the yield and stover attributes.
High cutting height of maize (two internodes below the lowest ear) allowed harvest of most of the stover (on average 63-72% in EM and MM genotypes, respectively) as feedstuff while leaving stubble in the field available for other uses. This is established practice by farmers in some regions. The amount and quality as a feedstuff of the upper and lower stover components varied (P<0.01) among genotypes. N and DMD were 0.05-0.09% and 1.7-3.6%, respectively higher (P<0.0001) in the upper fraction of the stover than in whole stover. Thus evaluation and estimation of the amount and quality of maize stover available as a feedstuff should consider harvest at high cutting height to increase quality. G x E interactions were observed in yield and in some stover attributes in the upper and lower fractions, but these were not consistent.
Common bean varieties varied (P<0.05 to P<0.0001) in yields of seed and haulm and in the nutritive value of haulm fractions (leaf, stem and pod wall) when harvested at seed maturity. There was extensive leaf loss at seed maturity which decreased haulm quality. Seed and haulm yields were correlated (r=0.87). Seed yield was generally not related to haulm quality as N% or DMD%. The variation in yield and haulm feedstuff quality was also examined in common bean varieties harvested at early seed maturity. Leaf proportion (23.1 vs. 6.9%), haulm N (1.53 vs.0.85%) and DMD (62.2 vs. 48.8%) were much higher at early harvest. G x E (site) interactions (P<0.05 to P<0.0001) were observed for yields of seed and haulm, and the N content and DMD of pod wall. Harvest at seed maturity increased (P< 0.0001) seed yield but reduced haulm yield.
To relate the research findings to farming systems a survey was conducted in three weredas/districts (Akaki, Shalla ad Misrak-Badawacho) in 2014 to examine the practices, perceptions and rationale of farmers in relation to their management of cereal and grain legume crops and their crop-livestock integration. The survey used participatory rural appraisal tools (semi-structured interviews and group discussions) followed by a household level survey (n=600). There was wide variation in agronomic practices (e.g. crop variety, seed rate, harvest procedure) affecting CR yield and quality and also in
farmers perceptions compared to the recommended practices. On average 77%, 58% and 29% of farmers adopted improved varieties of maize, common bean and chickpea, respectively, but this varied widely among districts. Seeding rates (and hence D) often differed substantially from recommendations. Regression models showed that the probability of increasing maize CR yield was associated with education level of the HH head in years, livestock wealth, proportion of adopters of improved maize varieties, mean distance to output market and total maize seed used in tonnes/HH.
In conclusion, these studies demonstrated that improved maize and common bean genotypes which combine high yield of grain or seed and CR and improved CR quality as feedstuffs can be identified for use as dual purpose crops. In maize higher D and modification of harvest procedure should provide options to increase the amount and value of CR as ruminant feedstuffs without reducing grain yield. Improved understanding of farmers practices and perceptions relevant to CR yield, quality and use and crop-livestock integration should hasten adoption of improved technologies and practices for enhanced
output from the whole farm.