ABSTRACT

Field experiments were conducted between 2016 and 2018 at Forestry Research Institute of Nigeria, Humid Forest Research Station, Umuahia, South east Nigeria, to study litter production, decomposition and nutrient release dynamics in Allanblackia floribunda (oliv) agroforestry system and espacement interaction on growth and yield of maize and mungbean. The experiments were all laid out in a randomized complete block design with three replications for the experiment on litter production, decomposition and nutrient release, and four replications for the alley cropping experiments. Litter trays were used for monthly collection of leaf litter while the litter bag method was employed for the decomposition study. In the first espacement experiment, there were four treatments comprising 2 maize spatial arrangements (single and double rows) between Allanblackia hedge rows and a no-tree control (maize monocrop in single and double rows) In the second espacement experiment, treatments were four and comprised 2 mungbean plant spacings (20cm x 20cm and 30cmx 20cm) between Allanblackia rows and a no-tree control (mungbean monocrop 20cm x 20cm and 30cm x 20cm spacing). Results indicated that the dry season months of November, December, January and February gave significantly higher leaf litterfall (23.76 – 43.50 kg/ha in 2016/17 and 34.75 – 151.22kg/ha in 2017/18) than the rainy season months (4.96 – 14.53 kg/ha in 2016/17 and 8.81 – 17.96 kg/ha in 2017/18). Leaf litter production positively and significantly correlated with maximum temperature and negatively correlated with rainfall and relative humidity, with a bimodal pattern showing leaf litter peak production in January and December. The C:N ratio was 10.6:1. The cumulative mean leaf litter decomposition at 48 WALP was 91.0%, with a biphasic mode of decay, having an initial rapid phase of mass loss (4 – 24 WALP) and a later slower phase (28 – 48WALP). Leaf litter half-life was obtained at 8 WALP while the turn over coefficient k (decay constant) was 4.62/year. The percentage cumulative mean nutrient release for N, P, K, Ca and Mg increased up to 24 or 28 WALP and thereafter stabilized up to 40 WALP, after which a slight decline in P, K, Ca and Mg and a significant drop in nitrogen. However, Organic carbon increased significantly up to 32 WALP, beyond which no significant changes occurred in the cumulative release from the leaf litter. At 10 and 12 WAP, maize double row regardless of cropping system produced significantly taller plants and higher leaf area index than maize single row. However, maize double row under sole cropping had significantly higher seed yield than maize under alley cropping, irrespective of maize spatial arrangement. Alley cropping and mungbean spacing did not significantly affect mungbean stem diameter and leaf area index. In contrast, mungbean spacings 20 x 20cm and 30 x 20cm under sole cropping produced comparable high seed yields (2.7 – 3.1t/ha) as the closer spacing of 20 x 20cm in alley cropping (2.6 t/ha) but significantly higher yields than the wider spacing of 30 x 20cm in alley cropping with Allanblackia floribunda tree species. The continuous leaf litter production throughout the year, the high rate of litter decomposition and subsequent release of nutrient make A. floribunda leaf litter a good source of organic manure for soil fertility restoration and improved growth and yield of arable crops (maize and mungbean). The early yield reductions observed in the A. floribunda agroforestry system could be substantially minimised if the trees are planted at wider spacing and pruning of tree branches and crown management are done regularly.