High and sustainable crop yields in the tropics have been reported to be only possible with judicious combination of mineral fertilizers and organic amendments. Fertilizing croppings to achieve this has usually been a difficult task to achieve. The growth and yield of maize cultivated with a complementary application of organic and inorganic fertilizers was assessed compared with sole organic and sole inorganic fertilizers between April and July 2003 and 2004 at Ibadan, Nigeria, in the degraded tropical rain forest zone. There was a no-fertilizer treatment as the control. The organic fertilizer was an equal mixture of composted domestic waste and stale cow dung, applied at 10 tonnes ha -1 . Urea and Single super phosphate were applied as the inorganic fertilizer to supply 70 kg N and 13 kg P 2 O 5 ha -1 respectively. The mixture of organic and inorganic fertilizer treatment consisted of half the rates used for sole organic and sole inorganic fertilizer treatments: 5 tonnes organic mixture was applied, with 35 kg N and 6.5 kg P 2 O 5. Maize plant height at 8 weeks after planting was highest with inorganic fertilizer application while the leaf area was highest with organic fertilizer application. Stover yield and cob yields were also highest with inorganic fertilizer. Complementary application of organic and inorganic fertilizers however had similar plant heights; stover yield as well as cob yields with inorganic fertilizer. Nitrogen appeared chelated with organic fertilizer application. Plant earleaf Nitrogen was highest (1.68%) with inorganic fertilizer while the control plots had a Nitrogen content of 1.12% which was higher than 0.84% and 0.98% N from sole organic and a complementary application of organic and inorganic fertilizers, respectively. Plant P content was increased by 136% and 15% with organic and inorganic fertilizers, respectively, but was reduced by 15% with complementary application of organic and inorganic fertilizers. The K content was highest with inorganic fertilizer (1.91%). Complementary application of organic and inorganic fertilizers had a K content of 1.70% while the organic -fertilized leaves had 1.53%. Stover nutrient uptake was highest for N and K with inorganic fertilizer while the P was highest with organic fertilizer application. Cultivating maize with complementary organic and inorganic fertilizers gives a comparable cob yield as inorganic fertilizer and has nutrients higher than from sole organic fertilizer application.

The changes in soil nutrient status following the application of different fertilizer types were studied in field experiments involving maize-melon intercrop relayed into a cassava-soybean intercrop between 1995 and 1997. The soil at the experimental site was a Kanhaplic Haplustalf, which was under continuous cultivation with arable crops for seven years and fallow for four years. The effects of organic and inorganic fertilizers were investigated singly and in combination.The type of fertilizer had no significant effect on the soil pH, although, cropping significantly lowered the pH from 6.0 to 5.7. Cropping also significantly reduced the soil organic matter and total nitrogen (N). The soil organic matter (OM) and total N were most depleted with organic fertilizer application. Complementary application of organic and inorganic fertilizers limited the degree of depletion from 31.0 to 12.1 g kg À1 of OM and 1.8 to 0.6 g kg À1 total N. Soil available P was increased (60%) by inorganic fertilizer while the organic fertilizer increased it by 145% and the combined fertilizer by 186%.Exchangeable calcium (Ca) was depleted by about 12% with organic fertilizer application, 15% by inorganic fertilizer and about 19% with complementary application of organic and inorganic fertilizers. Exchangeable sodium (Na) was reduced from 0.43 to about 0.38 cmol kg À1 while magnesium (Mg) was increased from 0.5 to about 0.6 cmol kg À1 .

Field trials were conducted in the forest vegetation (Ibadan) and the derived savannah (Ilora) zones of south west Nigeria to assess the yield performance of cassava/maize intercrop and soil nutrient changes with sole and some combined ratios of organic-based fertilizer (OBF) and inorganic fertilizer. Sole OBF was assessed at 2.5; 5.0 and 10.0 t ha -1 while 400 kg ha -1 NPK 15-15-15 served as the sole inorganic fertilizer treatment. The combined treatments were: 2.5 t ha -1 OBF + 100 kg ha -1 NPK 15-15-15 and 5 t ha -1 OBF + 100 kg ha -1 NPK 15-15-15. An unfertilized treatment served as the control treatment. Maize grain yield was highest with application of 5 t ha -1 OBF + 100 kg ha -1 NPK. It gave a mean yield of 2.45 t ha -1 at Ibadan and 2.49 t ha -1 at Ilora. Cassava root yield was however highest with 10 t ha -1 OBF. It gave a mean yield of 14.55 t ha -1 at Ibadan and 12.52 t ha -1 at Ilora. Soil N, P, K and Organic C was most increased with 10 t ha -1 OBF and 5 t ha -1 OBF+NPK. Crop yields and soil nutrient status decreased with no fertilizer application. Cassava -maize intercrop gives optimum yields and highest soil N, P, K increase with 10 t ha -1 OBF.

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