No abstract

The toxicity of nicosulfuron to none target organisms is its downside, which has generated concerns about the herbicide in spite of its high herbicidal activity. Practices that would facilitate accelerated degradation of this herbicide will certainly be complementary to its use. A completely randomized design laboratory incubation experiment was carried out to examine the potentials of organic and mineral fertilizers to stimulate microbial activities in soil under the influence of the nicosulfuron herbicide. Soil contaminated with the field rate of nicosulfuron was separately amended with compost and NPK mineral fertilizer, and the treated samples were incubated for 56 days at room temperature. Soil microbial activity and microbial biomass C were measured in dynamics for the period of incubation. Eco-physiological quotients were also computed at the end of incubation to determine responses of soil microbes at the community level to the treatments. Application of nicosulfuron alone was found to repress both microbial biomass and microbial activity. Addition of fertilizer however caused these parameters to increase especially during the first 28 days after treatment application. The microbial metabolic quotient was raised by the soil amendments shortly after application with the exemption of NPK treated soil. However, only the soil samples in which compost was present lowered qCO2 at the termination of the experiment. NIC-COMP and NIC-NPK respectively raised and lowered the soil carbon mineralization quotient (qM) measured at the end of incubation. The soil microbial community was also found to be positively affected by the addition of fertilizers as indicated by the Cmic: Corg ratio and the microbial biomass change rate quotient (qC). It was therefore concluded that though the nicosulfuron herbicide at the field recommended rate has potentials to negatively affect the soil microbial community, application of organic fertilizer may help the soil to regain its microbial competence through enhanced degradation engendered by biostimulation of native microorganisms.

14A short-term field and laboratory experiment was conducted to assess the impact of four 15 traditional tillage methods on the physical, chemical and biochemical properties of a sandy clay 16 loam alfisol under maize (Zea mays L.) cultivation following a fallow period of five years. 17Treatments included slash only (SO), slash +burn (SB), slash+ ridge (SR) and herbicide 18 (glyphosate) application (HA) at the recommended rate of 2 L/ha -1 . Results from the statistical 19 analysis of data from this study showed inconsistent trends of tillage treatments on soil physical 20 properties. However, slash +burn (SB) tillage significantly (p < 0.05) enhanced chemical 21 properties such as the soil pH, available P, exchangeable K + , Ca 2+ , and Mg 2+ compared to their 22 respective values before treatment application in the two years under study. Amongst the 23 treatments, slash + burn (SB) tillage further exerted the most significant (P ≤ 0.05) effect on 24 urease, L-asparaginase, L-glutaminase, dehydrogenase, acid and alkaline phosphatase activities, 25 but recorded the least values for amidase and β-glucosidase activities in soil. Results from this 26 study therefore, suggest that SB tillage treatment was beneficial to the soil environment as it has 27 proven to be more promising and effective for enhancing the selected soil quality indicators on 28 the soil type due to quick mineralization and release of bound nutrients present in the soil and 29 litter.30

Soil applied herbicides may persist to adversely affect rotational crops as well as perturb soil microbiological functions. This experiment therefore aimed at determining the effects of soil residual activity of diuron (3,4-dichlorophenyl)-N,N-dimethylurea) on Corchorus olitorius plants and on soil microbial population. Diuron herbicide was applied to potted soils at varying times of 12, 9, 6, 3 and zero weeks before planting Corchorus olitorius. Seed germination, seedling mortality, plant growth as well as soil microbial populations were determined. Results indicated that diuron, regardless of time of application significantly reduced growth parameters of C. olitorius plants few days after emergence, and this was followed by 100% die-back in the herbicide treated pots. Results further showed a reduction in soil microbial population with diuron application, and the reduction was inversely related to time of diuron application before sowing C. olitorius. Sensitive vegetables such as C. olitorius should not be sown to succeed a short season crop in which diuron had been applied to control weeds at the usual recommended rate of 3.0 kg a.i/ha. Allowance of a fallow period following the first crop might also help the soil microbial community to recover from diuron toxicity.

Neem seed cake has been reported to make nutrients available to support good growth of crops and increase yield. This ease of nutrient release is also required in a potential bio-stimulant. This study assessed the potentials of a neem seed-based fertilizer formulation as a bio-stimulant to aid continued nutrient mineralization from an organic source in contaminated soil samples. Neem seed-based organomineral formulation was added to soil samples contaminated with two field rates (40 and 60 mg.a. i ha -1 ) of nicosulfuron herbicide to assess their separate and interaction effects on soil microbial activity in the laboratory. The treated samples were incubated for 8 weeks, and soil microbial activity was monitored in dynamics for the period of incubation. Data on soil basal respiration, soil organic carbon, and soil carbon mineralization quotient (qM) were collected on weekly basis for the 8 weeks. Application of nicosulfuron alone regardless of rate repressed soil basal respiration; hence carbon mineralization in the early weeks of the incubation period, but these parameters were stimulated after the 5th week of incubation. Addition of the neem formulation on the other hand caused consistent significant stimulation from the beginning to the end of incubation. Results further showed that combining nicosulfuron and the neem formulation raised soil basal respiration significantly above what individual factor contributed. It was therefore concluded that although the individual factor was found to increase CO2-C compared to the control at the end of incubation, the interaction of the two inputs raised CO2-C even higher. This is an indication that the neem seed cake formulation has the potentials to cushion the adverse effects of nicosulfuron contamination on the soil microbial community.