ABSTRACT

Soil acidity has remained a major yield limiting factor for crop production worldwide, and in Umudike Southeastern Nigeria, where the soils are characterized by high acidity and low nutrient status, Incubation studies, field experiment and laboratory analysis were carried out to investigate the effects of biochar on soil acidity, pH-buffering capacity and nutrient status in an Ultisol planted to cucumber in Umudike, Southeastern Nigeria. The treatments were 0 tonne per hectare biochar, 1 tonne per hectare biochar, 3 tonnes per hectare biochar, 5 tonnes per hectare biochar, 1 tonne biochar + 400kg NPK (15:15:15) per hectare, 3 tonnes biochar + 400kg NPK (15:15:15)  per hectare, 5 tonnes biochar + 400kg NPK (15:15:15) per hectare and 400 kg NPK (15:15:15)  per hectare. The treatments were replicated 3 times. The incubation studies were carried out to investigate the effect of the treatments on soil pH and Exchangeable acidity of the soil under study over a period of four weeks, using the equivalent of the treatments used in the field experiment, 0g biochar, 1.6g biochar, 5g biochar, 8g of biochar, 1.6g biochar + 0.6g NPK(15:15:15), 5g biochar +0.6g NPK(15:15:15), 8g biochar +1.6g of NPK(15:15:15) and 0.6g of NPK(15:15:15). Each of the treatments was added to 50g of soil in plastic containers of equal size and basal diameter and replicated three times. The soil used for the incubation studies was strongly acidic, having a pH (H₂O) of 4.38 and exchangeable acidity of 1.84. The soil pH (H₂O) and Exchangeable acidity were determined on the incubated samples at weekly interval for 4 weeks, using standard laboratory procedures. The effect of the treatments on the pH-buffering capacity of the soil during incubation was also determined using standard procedures. Results obtained showed that 5 tonnes per hectare biochar significantly (P<0.05) increased soil pH from 4.38 to 8.1, 8.64, 8.20 and 8.42 from week 1 to week 4 of incubation respectively, while Exchangeable acidity was reduced from 1.84 to 0.34, 0.61, 0.56 and 0.37 from week 1 to week 4 respectively throughout the incubation period. The pH-buffering capacity of the incubated soil was also increased by 96%, 97%, 87% and 92% from week 1 to week 4 respectively. The field experiment was laid out in a randomized complete block design and conducted at Michael Okpara University of Agriculture Eastern Farm. The soil used for the experiment was strongly acidic, having a pH (H₂O) of 4.50 and exchangeable acidity of 1.44 cmolkg^-1. The variety of cucumber planted was “Market More” and the result obtained from the field experiment indicated a significant (P<0.05) increase in the number of leaves and vine length of cucumber by 3 tonnes biochar + 400 kg NPK (15:15:15) per hectare over other treatments. It could therefore be inferred that the application of biochar as soil amendment can viably ameliorate soil acidity, increase soil pH-buffering capacity, enhance nutrient status and invariably improve cucumber growth in the soils of the study area.