Effects of Methods of Seedbed Preparation and Organic Amendments on Soil Properties, Growth and Yield of Sunflower (Helianthus annuus L.) in a Humid Zone of Nigeria

Aims: Field experiments were conducted to evaluate the effects of methods of seedbed preparation via clearing of existing vegetation and organic amendments on some soil properties, growth and yield of sunflower (Helianthus annuus L.).

Study Design: The treatments consisted of 2 by 3 factorial combination of bush clearing methods and organic amendments arranged in a split- plot design.

Place and Duration of Study: The experiments were conducted in the late season of 2009 and late season of 2010 at the Teaching and Research Farm of the Federal University of Technology, Akure, Nigeria.

Methodology: The treatments consisted bush clearing methods, manual clearing and herbicide-based zero tillage, were the main plots while organic amendments via application of organic fertilizer and farmyard manure constituted the subplot treatments. Measurements were made on soil properties: physical,(soil moisture contents and temperature), chemical (soil pH, organic matter, N, P, K, Ca, Mg) and biological (bacterial and fungal counts).

Results: The results show that herbicide–based zero tillage plus organic manure produced the highest values of soil organic matter (4.2 g kg-1 and 4.5 g kg-1) in 2009 and 2010 respectively compared with manual clearing plus organic manure (4.0 g kg-1 and 4.2 g kg-1) in 2009 and 2010 respectively. Herbicide–based zero tillage plus organic fertilizer had higher values of organic matter (3.9 g kg-1) in 2009 experiment compared with manual clearing plus organic fertilizer (3.8 g kg-1). In the respective bush clearing methods, application of organic manure increased soil organic matter content. Organic amendments improved the soil micro- environment around the plant compared with unmanured plots with increases the populations of soil bacteria and fungi. Non significant differences were obtained in soil temperatures between bush clearing methods alone and in combination with organic amendments. There were small differences in soil moisture contents between bush clearing methods alone and in combination with manuring. Herbicide-based zero tillage plus organic fertilizer produced values of plant height and stem girth (1.25 m, 2.80 cm and 1.10 m, 2.21cm) which were not significantly different (P > 0.05) from values ( 1.21 m, 2.70 cm and 1.08 m, 2.00 cm) under manual clearing plus organic fertilizer. Although organic amendments improved growth and yield components of sunflower over the unamended, no significant differences (P > 0.05) were found for most of the parameters measured. The effects of bush clearing methods were also not significant on growth and yield components of sunflower. Herbicide-based zero tillage plus organic fertilizer produced higher seed yields and is therefore recommended for sunflower production in the study area.

Conclusions: Organic amendments and herbicide–based zero tillage had positive effects on soil and sunflower productivity, this practice is recommended for sunflower production in the study area.