Effect of different sources and proportions of biochar on soil carbon sequestration rates and yield of maize (zea mays L.)
This study investigated the chemical properties of the biochars produced from different plant wastes and assessed the effects of their applications as soil amendments on the growth performance, yield as well as the nutritional quality of maize. It also assessed their effects on the soil carbon and nitrogen dynamics and the rate of soil carbon sequestration. This was with a view to determining the residual effects of the treatments and identifying optimal strategy for enhancing carbon sequestration in soils. The study was carried out in two phases; at the screenhouse of the Faculty of Agriculture and on the Teaching and Research Farm of the Obafemi Awolowo University, Ile-Ife, Nigeria. Biochars produced from cocoa pod husk (CPH), maize stovers (MAS) and maize cobs (MAC) were characterized using standard methods. Surface soil samples were collected from an exhaustively cropped land; air-dried and sieved through a 2 mm mesh. Ten kilograms of the sieved soil was filled into each plastic pot perforated at the bottom to enhance soil aeration. The screenhouse experiment consisted of six different treatments [CPH, MAS and MAC applied singly and in equal combination (CPH50MAS50, CPH50MAC50 and MAS50MAC50)]. All the treatments were applied at different rates (0, 5, 10, 15, 20, 25 tonnes/ha) and each replicated thrice in a completely randomized design to give a total of 108 pots. The biochars were thoroughly incorporated in the soil, watered and incubated for seven days. Maize seeds (ART/98/SW6) earlier purchased from Institute of Agricultural Research and Training, Ibadan, were sown at four seeds per pot and thinned to two stands at two weeks after sowing. Screenhouse experiments were conducted twice, but treatments were applied once. The field experiment was laid out in a randomized complete block design with twelve plots, each measuring 3.0 m x 2.5 m with an alley of 1.0 m between and within plots. The treatments included MAS and MAC applied at 10 t/ha and no biochar serving as control, each with four replications. Maize was sown at three seeds per hole using 75 cm x 50 cm planting distance and thinned to two stands per hole two weeks after sowing. Field experiments were conducted in the dry and wet seasons. Data on growth parameters, grain yield and proximate compositions of the grains were determined. Pre-and post-cropping soil tests of the screenhouse and field were carried out using standard methods. Data obtained were subjected to two-way ANOVA and descriptive statistics. The pre-cropping soil pH in 1:1 soil-water suspension was 7.94 and 5.89 for the screenhouse and field experiments respectively. The soil texture was sandy loam. Biochars’ pH ranged from 10.77 to 11.98. The C/N ratios of the biochars were: 58.93, 44.35 and 42.23 for CPH, MAC and MAS respectively. At the screenhouse, the highest mean plant height of 160.2 ± 12.97 cm was obtained when soils were amended with MAS biochar at 25 t ha-1. Similar results were obtained with the stem girth and number of leaves. Significantly (F70, 107 = 1.88; p > 0.05) highest grain yield of 4.27 t ha-1 for MAS at 15 t ha-1 was obtained in the first cultivation. The repeat experiment at the screenhouse gave comparable but lower values. In the field, MAS biochar at 10 t ha-1 had superior positive effect on the growth components of maize when the three treatments were compared. The highest mean yield of 1.50 t ha-1 (dry season) and 1.51 t ha-1 (wet season) obtained with MAS biochar was not significantly (F4, 8 = 0.994; p > 0.05) higher than 1.45 t ha-1 for dry season, but significantly (F4, 8 = 32.87; p < 0.05) higher than 1.11 t ha-1 for wet season. Maize grains from the control plots had the highest crude protein (9.72%) and ash contents (3.84%) in the dry season. Comparable, but lower values were obtained in the wet season. The MAS biochar had higher potential for carbon sequestration with 12.45 t C ha-1 yr-1 as about 79% of the initial organic carbon remained in the soil after the two consecutive maize cropping. This study concluded that biochar application enhanced the yield, but not the quality of maize. The high residual organic carbon content indicated that biochars could be potential feedstocks for carbon sequestration.