PHYSICOCHEMICAL PROPERTIES AND PRODUCTIVITY OF 2 TROPICAL SOILS AMENDED WITH DEHYDRATED SWINE WASTE

With maize (Zea mays L.) as the productivity indicator crop, the fertilizing value of dehydrated swine waste (DSW) was assessed on two texturally contrasting tropical soils, a sandy Kandic Paleustult (S-l) and a clayey Lithic Usorthent (S-2). The treatments were different rates of DSW and inorganic fertilizer (F): 0%; 2.5%; 2.5%+F; 5.0%; 5.0%+F; 7.5%; 7.5%+F; 10.0%; 10.0%+F; and F alone. The F treatment consisted of the locally recommended rates of N, P, K and Mg for maize production. On both soils, high rates of DSW (greater than or equal to 5.0%) delayed maize germination. Maize height and dry-matter yield increased with DSW rates, with the highest yield obtained at the 10.0%+F treatment. On all treatments, yield was consistently better on the more fertile S-2 than on the S-1 soil. All treatments including DSW out-performed the F-alone treatment because of higher nutrient contents of the organic waste-amended soils. The amounts of N, P, K, Ca and Mg released during the study explained individually between 66 and 73% of variation in maize yield on both soils. The C:N ratio of the treatments had an indirect effect on maize performance, explaining between 91 and 95% of the variation in yield. Increasing races of DSW progressively increased the soil pH, organic carbon, N, P, exchangeable Ca, Mg, K and CEC, and reduced the exchangeable acidity at the end of the experiment. Also, the moisture retention capacity of both soils increased at all matric potentials between 0 and - 1500 kpa following DSW application. Even though the water-dispersible clay increased slightly with high DSW rates (implying reduced stability at the colloidal level), the overall effect of the organic amendment was towards enhanced resistance of the macro aggregates to disruptive water forces. Improvement in these physico-chemical properties was a direct consequence of increased organic matter levels following the DSW application to the soils.