Aggrading lateric soils (ultisol) using biochar

Abstract

The present investigation was undertaken at College of Horticulture, Vellanikkara and Agricultural Research Station, Mannuthy during 2016-2018. The study consisted of production and characterization of bioehar from coconut based materials, an incubation experiment, and two field experiments. The incubation experiment was conducted for 15 months to study the dynamics of C and N in soil over time and the soil samples were analyzed for C and N fractions at three months' interval. Two field experiments were carried out sequentially, wherein Chinese potato was raised to study the direct effect of bioehar and vegetable cowpea was the test crop to study the residual effect of bioehar applied to the first crop. Three levels of bioehar (5, 7.5, 10 t ha"'), FYM 10 t ha"', soil test based POP + bioehar 10 t ha"' and soil test based POP were the treatments, for both incubation and field experiments. Soil test based POP consisted of NPK and FYM 10 t ha"'. Control plots without the addition of biochar/fertilizers were also maintained. Recovery of bioehar from coconut husk and shell (1:1) on pyrolysis was 22 per cent. The produced bioehar had an alkaline pH (10.01), high EC (3.42 dS m"'), C (64.14 %), CEC (15.78 cmol (+) kg"'), and C: N ratio (113:1). Total N, P, K, Ca, Mg and S contents were 0.567, 0.982, 4.175, 1.19, 0.456 and 0.244 per cent, respectively. Regarding physical properties, bioehar had low bulk density (0.128 Mg m"^), very high porosity (84.63 %) and WHC (307.3 %). Basicity and acidity of bioehar were 2.02 and 0.08 mmol g"', respectively. The surface morphology and chemistry studied using SEM, TEM, FT-IR and Raman spectroscopy revealed the porous, aromatic and recalcitrant nature of bioehar and the presence of functional groups mainly carboxyl, hydroxyl and carbonyl. Results of incubation experiment revealed that the content of organic carbon - (OC), water soluble carbon (WSC) and microbial biomass carbon (MBC) increased up to 6 months of incubation and decreased thereafter. In the case of permanganate oxidizable carbon (POXC) and hot water soluble carbon (HWSC), a decreasing trend was noticed. While the highest value of WSC and HWSC were recorded in FYM 101 ha"', all other C fractions were higher in the treatments viz. soil test based POP + bioehar 10 t ha"' and bioehar 10 t ha"'. With an increase in levels of bioehar, the labile C fractions viz. POXC and MBC increased. The labile C fractions in soil were in the order POXC > HWSC > MBC = WSC. As regards the N fractions, NH4-N declined steadily at 3 months, then increased up to 9 months of incubation after which it decreased till the incubation ended. The NO3-N and amino acid N increased up to 12 months of incubation and slightly declined thereafter. Increase in total hydrolysable N was noticed up to 6 months of incubation and thereafter, a progressive decrease was noticed. While the total N content decreased over the incubation period, the KMn04-N increased. With an increase in levels of biochar, the NO3-N and KMn04-N increased. The treatments soil test based POP + biochar and soil test based POP were equally superior to other treatments with respect to N fractions. Results of field experiments revealed the superiority of biochar 10 t ha"' in increasing soil pH and NH4OAC-K and reducing the exchangeable acidity. The treatments soil test based POP + biochar and soil test based POP were superior with respect to most of the soil properties. Application of biochar at 10 t ha"', either alone or in combination with POP improved the soil properties viz. OC, dehydrogenase activity, CEC, MWHC and hot water soluble B. With an increase in levels of biochar, the soil properties viz. pH, CEC, WHC, dehydrogenase activity, NH4OACK, Ca, HCl-Zn and humic acid increased. With respect to the growth parameters and yield of Chinese potato, application of soil test based POP + biochar and soil test based POP were comparable. The same treatment soil test based POP + biochar that faired in terms of direct effect proved good in residual effect as well, as reflected from the plant growth and yield of cowpea. Path analysis had shown that the soil properties viz. OC, MBC, Bray-P, NH4OAC-K, Ca and EC directly influenced the tuber yield, reinstating the role of biochar in yield improvement. The nutrient content in plant parts and its uptake varied among treatments and corroborated the trend. Considering the quality attributes of Chinese potato, the treatments biochar 10 t ha"' and soil test based POP + biochar recorded higher CHO content. Protein content was highest in the treatments soil test based POP and soil test based POP + biochar. The advantage of biochar on increasing protein content and decreasing crude fibre content was visible in the succeeding crop of cowpea also, thus establishing its high residual effect. The study revealed the potential of biochar as an amendment in the highly weathered, nutrient-poor acidic laterite soils of the tropics. Its application brought about increase in soil pH, addition of basic cations, improvement in CEC and WHC, and gradual release of nutrients to the growing plants. The overall improvement in physical, chemical and biological soil conditions through biochar could promote plant growth, yield as well as quality. The positive effect of biochar could be observed in combination with soil test based fertilizer application also.