Nutrient Cycling in Agroecosystems 54: 145–155, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 145 Longterm alley cropping with four hedgerow species on an Alfisol in southwestern Nigeria – effect on crop performance, soil chemical properties and nematode population B.T. Kang ∗ , F.E. Caveness, G. Tian & G.O. Kolawole International Institute of Tropical Agriculture (IITA), PMB 5320, Ibadan, Nigeria ( ∗ corresponding author: present address: 15 Beechwood Drive, Haverhill, MA 01832, USA; e-mail: iita@cgnet.com) Received 30 July 1997; accepted in revised form 26 June 1998 Key words: alfisol, biomass and nutrient yields, crop yield, nematodes, soil properties, tillage Abstract A longterm alley cropping trial was undertaken on an eroded Oxic paleustalf in the forest-savanna transition zone of southwestern Nigeria from 1981–1993. Two nitrogen fixing hedgerow species (Gliricidia sepium and Leucaena leucocephala) and two non legume hedgerow species (Alchornea cordifolia and Dactyladenia barteri) were used in the trial compared to a control (with no hedgerow) treatment. Plots were sequentially cropped with maize (main season) followed by cowpea (minor season). With 4 m interhedgerow spacing and pruning at 0.75 m height, the mean annual pruning biomass yields were observed in the following order: Leucaena (7.1 t ha −1 ) > Gliricidia (4.9 t ha −1 ) > Alchornea (3.7 t ha −1 ) > Dactyladenia (3.0 t ha −1 ). Alley cropping with the four woody species greatly enhanced the total plot (woody species + crop) biomass yield/ha as follows; Leucaena (21.8 t ha −1 ) > Gliricidia (17.7 t ha −1 ) > Alchornea (11.7 t ha −1 ) > Dactyladenia (9.5 t ha −1 ). Total biomass yield of crops in control plot was 5.3 t ha −1 . Higher biomass yields with alley cropping also increased nutrient yield and cycling. Gliricidia and Leucaena showed higher nutrient yields than Alchornea and Dactyladenia. Alley cropping with Gliricidia and Leucaena could sustain maize yield at moderate level (>2 t ha −1 ), which would require a N-rate of 45 kg N ha −1 with sole cropping. Application of N in Gliricidia and Leucaena alley cropping still improved maize yield. Higher nitrogen rates are required for alley cropping with Alchornea and Dactyladenia hedgerows. A low rate of phosphorus application is needed for sustaining crop yields with all treatments. Occasional tillage is recommended to increase maize yield. Alley cropping and tillage showed little effect on cowpea seed yield. Surface soil properties declined with time with continuous cultivation. Alley cropping with woody species maintained higher soil organic carbon, phosphorus and potassium levels. Plots alley cropped with Gliricidia and Leucaena showed lower pH and extractable calcium level. Leucaena alley cropped plot also showed lower magnesium level. The decline in soil pH and extractable cations may be due to increased cation leaching with application of high rates of Gliricidia and Leucaena prunings. Alley cropping with the four woody species showed no effect on population of parasitic nematodes. Introduction To farm the rainfed uplands in humid tropical Africa, traditional farmers have for generations employed conservation farming methods to sustain the continu- ity of their subsistence production system. However, in many areas of humid tropical Africa traditional farming is no longer sustainable due to shortening or disappearance of the fallow period resulting from rapid population growth. This leads to overexploita- tion of the natural resources and soil degradation. Considering the heterogeneity of farming systems and practices in the region, there is a dire need for alterna- tive farming methods that can sustain or enhance soil productivity, while at the same time conserve the re- source base with the use of affordable chemical inputs. Many decades of research have thus far only produced limited results.