The study was carried out at Domita Farms, located in Uyo, Akwa Ibom State to evaluate the comparative effects of palm bunch waste and calcium carbonate on selected soil properties under yam cultivation. It was also carried out to determine which soil properties were associated with the highest yield of white yam (Dioscorea rotundata). The design of the experiment was a split plot of 2 main factors (CaCO3 and PBW) and amendment rates (5) as sub-plots were applied at the rates of 0, 1.5, 3.0, 4.5 and 6.0 tonnes/ha. The soil was analysed for selected soil properties before and after the application of treatments. The data obtained were statistically analyzed and correlation analysis was used to test relationship among selected soil properties. The test of the soil 14 weeks after treatment showed that PBW increased OM, FMC, AWC and TP more significantly than lime, while lime increased soil pH, PWP, BD and yam yield more than PBW. With respect to amendment rates OM, TP, PWP, AWC, pH and FC increased generally significantly as both amendment rates increased but more under PBW than under CaCO3. On the other hand, BD and PWP decreased significantly at higher rate of PBW treatment. In relation to correlation, pH, BD and OM had high positive correlation with yam yield, indicating therefore that they contributed highly to the yield. It was revealed that the highest rate of palm bunch treatment (6.0tons/ha) affected the soil properties most strongly and positively. Therefore, application of PBW at 6.0 or more tons/ha, for the purpose of improving soil condition, is highly recommended.
The use of soil amendments is a way of reducing soil degradation and improving its quality in support of higher crop yields, especially in the long-term (Doran et al, 1996). Applications of fertilizers and amendments directly and indirectly affect soil chemical and physical properties. Such physical processes as aeration, bulk density, water holding capacity and soil reaction are significantly affected when inorganic or organic materials like amendments and fertilizers are applied to the soil (Zebarth et al., 1999; Trans, 2002; Celik et al, 2004). The application of soil amendments in the process of adjusting soil pH or adding certain nutrients do therefore cause changes in soil properties which if not properly controlled can degrade soil quality (Smaling and Braun, 1996).
Amendments material such as CaCO3 and CaMg (CO3)2 which are inorganic will likely affect soil physical and chemical properties differently than organic materials such as Palm Bunch Waste (PBW) and chopped cocoa pods (Gruhn et al 2000). PBW might decrease bulk density more than limestone, while limestone might add more Ca than PBW (Nekesa, 2007, Kinsinyo et al 2009). The different effects of various soil amendments on soil physical properties have indeed not been as widely reported as have their effects on soil chemical properties. It is important that the effects of amendments, whether organic or inorganic, on soil physical properties be better understood so that their use may be properly managed in relation to type of amendment and type of soil. Serious research is therefore required for determinations of what changes occur to bulk density, field moisture capacity and other selected physical properties of the soil. The aim of this study was to determine by comparative evaluation, the effect of palm bunch waste (an organic amendment) and calcium carbonate (inorganic amendment) on selected soil properties under white yam (Dioscorea rotundata) cultivated in an ultisol, Akwa Ibom State.
SPECIFIC OBJECTIVES OF STUDY
The specific objectives of the study were:
To compare the effects of CaCO3 and PBW on selected soil properties viz: bulk density, field moisture capacity and porosity as well as pH and organic matter.
To determine the impacts of the amendment materials on selected soil properties.
To identify which of the soil properties affected by the treatments were associated with higher yields of yam as the test crop.