Improved fallows and relay cropping technologies as alternatives to shifting cultivation in Morogoro, Tanzania: an overview

Abstract

The project was initiated in 1995 to evaluate improved fallows and relay cropping technologies as alternatives to traditional shifting cultivation in semi-arid areas of Morogoro. Two study sites were selected and these were Sokoine University of Agriculture (SUA) Farm and Gairo site.The project involved the following studies: tree/shrub provenance trials and the species evaluated included Sesbania sesban, S. macrantha, Gliricidia sepium, Calliandra calothyrsus, Casuarina equisetifolia/ junghuhniana; evaluation of species and time for improved fallows and relay cropping in which two two-year improved fallow experiments involving S. sesban, S. macrantha, G. sepium and C. cajan were carried out at both sites. In addition a 1, 2 and 3 year fallow experiment involving S. sesban, C. cajan and Tephrosia vogelii was carried out at Gairo. The others were, effect of green manure on solubilization of Minjingu Rock Phosphate, effect of P fertilization on growth of selected leguminous tree/shrub species in the nursery and in the field and effect of spacing on growth and yield of Sesbania sesban.For S. macrantha, overall the Andago, Bihalamulo and Chala provenances were the best performers at Gairo site. For C. calothyrsus, Union Juarez, San Ramon and Flores performed best for Morogoro site while Fotuna and Cafradia performed best at Gairo site. Data for S. sesban, G. sepium and Casuarina provenances is being analysed.In a two year improved fallow study at Gairo, S. sesban was the best fallow species in wood production with a wood biomass yield of 19.20 t ha-1. In maize grain yield, G. sepium was outstanding with a yield of 3.66 t ha-1, which is 205% higher than the yield from the natural fallow. In a 1, 2 and 3 year fallow experiment 2 years was found to be the best fallow period. Wood production from 2 year fallows of the tested species was S. sesban 51.79 t ha-1, T. vogelii 4.59 t ha-1and C. cajan 5.19 t ha-1. Maize grain yield from the 2 year improved fallows of S.sesban, T. vogelii and C. cajan without fertilization was 2.47, 4.41 and 2.47 t ha-1 respectively. The corresponding increase in maize grain yield against the natural fallow was 97.6%, 252.8% and 97.6%. For the relay intercropping of S. sesban, maize grain yield from plots with or without S. sesban was 2.28 and 1.88 t ha-1 respectively. Due to the smaller percentage increase (21%) in yield, S.sesban is not suiTable for use in relay intercropping at SUA Farm. For the effect of P fertilization on the growth of selected tree/shrubs experiment, P fertilization increased the periodic mean height increments though not significantly. Phosphorus application levels significantly increased the foliar N and P of S. sesban and T. vogelii. In the effect of green manure on solubilisation of MRP study, the highest maize grain yield of 2.60 t ha-1was obtained where incorporation of green manure was adopted. In the spacing experiment the highest wood biomass production (39.02 t ha-1) was achieved at closer spacing and the lowest (11.08)at wider spacing.Based on the results of this study the following are recommended: (i) On farm trials of T. vogelii and G. sepium should be initiated so as to substantiate the potential of these species for use in improved