Thesis and Dissertation for the Department of Agronomy

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    IMPROVEMENT OF SOIL QUALITY AND MAIZE (Zea mays L.) PERFORMANCE USING SELECTED WEED SPECIES AS SOIL AMENDMENT
    (UNIVERSITY OF ILORIN, 2018-07) YUSUF, SAIDU ADEWUMI
    Continuous cropping and poor soil management have resulted in reduced crop yield in southern Guinea savannah (SGS) zone of Nigeria. Effective soil management strategy to restore essential soil nutrients is thus required. Thisstudy assessed the potential of selected weed species as soil amendment for improved soil quality and crop performance in SGS. The specific objectives of the study were to: (i) assess the effect of soil amendments on the soil microbial population, succession and diversity; (ii) evaluate the effects of the combination of varying rates of the amendments on soil properties; (iii) evaluate the effect of the amendments on soil productivity using maize as test crop; and (iv) investigate relationships between soil quality indicators and maize yield components. Weed species(Amaranthus spinosus, Aspilia africana and Chromolaena odorata)were screened for ability to improve soil quality and maize performance in a preliminary potted experiment using a complete randomized design (CRD).C. odorata was selected for the field experiment. A randomized complete block design (RCBD) was adopted for field experiments conducted in2014 -2015 growing seasons with application ofC.odorata at 10 t/ha and 15t/ha singly and in combination with NPK (60-30-15kg/ha) as well as sole application of NPK (120-60-30kg/ha) in maize plots. The plate culture technique was used for microbial analysis of soil dilutions. Data collected on soil and yield computed were subjected to analysis of variance. Pearson Product Moment correlation coefficient was used to establish relationships between the measured soil quality indicators and maize yield components. The findings of the study were: (i) soil amendment with C. odorata increased soil microbial population (22.73%)and diversity (11.11 %) within the first four weeks of application. Proliferation of saprophytes and suppression of pathogens were observed as decomposition C. odorataprogressed; (ii) soil amendment with 7.5 % w/w C. odorata gave significantly (P≤ 0.05) higher; mean soil moisture content (SMC), 60.97g/kg, total porosity, 48.73%, bulk density, 1.36 g/cm3 and grain yield, (72.40 g/plant) than other treatments; (iii) C.odorata at 15t/ha combined with NPK fertilizer (60-30-15kg/ha) on the field, increased soil organic matter (SOM) and ECEC by 80.91% and 72.36% respectively after second year harvest. This rate had significantly higher values of mean SMC (76.40g/kg), total porosity (49.43%), % water filled pore spaces (20.68%) and lower bulk density (1.39 g/cm3 to 1.34g/cm3) at the end of second cropping season than other treatments; (iv) C. odorata at 15 t/ha combined with NPK(60-30-15 kg/ha) produced significantly higher mean maize cobs weight (11.46kg/plot), mean grain yield (4.67t/ha) (v) SOM was positively correlated with soil exchangeable bases, total N and available P with correlation coefficient (r) ranging from 0.65- 0.93. Mostmeasured yield components were also strongly correlated with each other with r ranging from 0.13 to 0.99. It was concluded that C.odorata has great potential for use as soil amendment in SGS zone to improve soil productivity. Application of 15 t/ha of C. odorata combined with NPK(60-30-15 kg/ha) was recommended for improved soil quality and maize performance in the region.