PORE SIZE DISTRIBUTION AND SOIL HYDRO PHYSICAL PROPERTIES UNDER DIFFERENT TILLAGE PRACTICES AND COVER CROPS IN A TYPIC HAPLUSULT IN NORTHERN NIGERIA

Tillage practices influence soil physical, chemical and biological qualities which in-turn alters plant growth and crop yield. In the Northern Guinea Savanna (NGS) ecological zone of Nigeria, agricultural production is mainly constrained by low soil nutrient and water holding capacity, it is therefore, imperative to develop appropriate management practices that will give optimal soil hydro-physical properties for proper plant growth, effective soil and water management and environmental conservation. This study investigated the effect of three tillage practices (no till, reduced till and conventional till) and four cover crops (Centrosema pascuorum, Macrotyloma uniflorum, Cucurbita maxima and Glyine max) and a bare/control (no cover crop) on some soil physical properties of a Typic Haplusult during the rainy seasons of 2011, 2012 and 2013 in Samaru, NGS ecological zone of Nigeria. The field trials were laid out in a split plot arrangement with tillage practices in the main plots and cover crops in the subplots, all treatments were replicated three times. Auger and core soil samples were collected at the end of each cropping season each year in three replicates from each treatment plot at four depths (0-5, 5-10, 10-15 and 15-20 cm). Particle size distribution, bulk density, total pore volume and water retention at various soil matric potentials were determined using standard methods. Data obtained were compared with optimum values and fitted into a RETC computer code for quantifying soil hydraulic behavior and physical quality. Results showed that different tillage practices had varied effect on soil physical properties. No-till had the highest water holding capacity at most suction points evaluated, it had 4.3 % and 12.9 % more soil moisture than the reduced till  and conventionally tilled systems across all matric potentials while Centrosema pascuorum (3.1%) and Cucurbita maxima (5.5%) were best among evaluated cover crops in retaining soil moisture content compared to the bare plots at -33kPa matric potential. Generally the Dexter S value used as an index for soil physical quality ranged within the limits of very good to good soil physical quality irrespective of the tillage practice, cover crops grown or depth of soil sampling. However the conventional tillage practice and soil under no cover crop had adverse effect on soil structural stability, placing them at a high risk of soil degradation. Indicators like Macro porosity, Air capacity, relative field capacity and Plant available water capacity were all within the optimal range for normal plant growth. The RETC computer code well described soil hydraulic parameter regardless of the treatments imposed on the soil.