AbstractAn experiment was established on a San Antón soil (Cumulic Haplustolls) in southern Puerto Rico to evaluate the effect of chicken manure (0, 5, 10 and 15 t/ha) and nitrogen fertilizer (0, 56, 112 and 168 kg/h) on some soil chemical properties and tomato production. Chicken manure was broadcast and incorporated into the soil whereas urea, the nitrogen source, was applied by fertigation. A significant lineal effect was observed in exchangeable Mg2+ and K+, electrical conductivity and Olsen available P with chicken manure applications. In the check treatment (no manure), exchangeable Mg2+ was 2.54
cmolc/kg; exchangeable K+, 0.99 cmol./kg; electrical conductivity, 0.79 mmhos/cm; and available P, 52.58 mg/kg. The application of 15 t/ha of chicken manure increased exchangeable Mg2+ to 2.70 cmolc/kg, exchangeable K+ to 1.29 cmolc/kg, electrical conductivity to 2.22 mmhos/cm and available P to 83.98 mg/kg. Soil pH decreased significantly with the same treatment from 7.50 in the check treatment to 6.98 in the 15 t/ha chicken manure treatment. Chicken manure increased soil exchangeable NO3- at a depth of 20 cm, but did not increase exchangeable NH4+. Application of chicken manure did not increase tomato yield significantly; however, it increased significantly the number of large and medium fruits. It is suggested that an exchangeable NO3- content of about 15 to 20 mg/kg is adequate for optimum tomato production in a San Antón soil.