Application of biochar alters availability of nutrients and acidic cations in soils which in turn could affect growth of plant to different degrees. Effect of rubber wood biochar amendment on the growth and nutritional status of Hevea nursery plants was determined in this study. Biochar were applied at 1% and 2% (w/w) with and without the recommended rates of N and Mg liquid fertilizers (LF). Two control treatments with 0% biochar but with and without recommended levels of all N, P, K, and Mg LF were also included. Application of biochar alone has a significant positive effect on above ground dry matter accumulation of the rootstock seedling (81% over the 0% biochar + no LF control) while no effect on the scion growth. Growth of plants in LF added treatments were much higher. Combining 2% biochar with N and Mg significantly increased the above ground dry matter accumulation over N-P-K-Mg only treatment in both rootstock seedling (29%) and the scion (61%). Biochar only application did not affect the N and P and decreased K and Ca concentrations in leaves. When combined with N and Mg fertilizers however, biochar significantly increased total N, P, Mg and Ca uptake. Biochar only application (2%) significantly decreased the leaf Mn concentrations in the seedling probably due to decrease in Mn availability as a result of increase in soil pH. The increase in soil pH due to biochar addition decreased with time close to original values in soils that received LF, possibly due to sulfate of ammonia. We concluded that application of rubber wood biochar (upto 2% w/w) could improve the growth of Hevea plants with the use of only N and Mg fertilizers under nursery conditions tested in this experiment.

Understanding carbon mineralization dynamics of organic amendments is essential to restore degraded lands. This study focused on the restoration potentials of tea-growing soils using organic materials available in tea ecosystems. The Selangor-Briah soil series association (Typic Endoaquepts) consisted of a high- (soil A) and a low-carbon (soil B) soils were incubated with different organic materials and released carbon dioxide (CO₂) measured. Two kinetic models were applied to depict the mineralization process. Soil health parameters including microbial biomass carbon and nitrogen, dehydrogenase and catalase activities were determined to assess the restoration potentials. The parallel first-order kinetic model fitted well for all amendments. Gliricidia markedly enhanced the net cumulative CO₂ flux in both soils. Charged biochar, tea waste and Gliricidia improved the microbial biomass carbon by 79–84% in soil A and 82–93% in soil B, respectively. Microbial quotients and biomass nitrogen were increased over 50 and 70% in amended soils, respectively. Dehydrogenase activity was significantly accelerated over 80% by compost, charged biochar and tea waste. Charged biochar remarkably increased the soil catalase activity by 141%. Microbial biomass, dehydrogenase and catalase activities, and cumulative CO₂ flux were positively correlated (r > 0.452) with one another. The studied amendments showed greater potential in improving the soil quality, while charged biochar, raw biochar and compost enrich the soil recalcitrant C pool ensuring the soil health in long term. Even though biochar sequesters carbon, it has to be charged with nutrients to achieve the soil restoration goals.

Anaerobic conditions developed during flooding can increase phosphorus (P) losses from soils to waterways. Soil amendment with gypsum (CaSO₄·2H₂O) can effectively reduce flooding‐induced P release, but its effectiveness is soil dependent, and the reasons are poorly understood. The objectives of this study were to reveal the possible inorganic P transformations during flooding of two soils (acidic‐Neuenberg sandy loam [NBG‐SL] and alkaline‐Fyala clay [FYL‐Cl]), with and without gypsum amendment prior to flooding. Porewater samples collected at 0, 35, and 70 d after flooding (DAF) from soils incubated in vessels were analyzed for dissolved reactive P (DRP); pH; and concentrations of calcium (Ca), magnesium, iron (Fe), manganese, chloride, nitrate, sulfate, and fluoride. Thermodynamic modeling using Visual MINTEQ software and chemical fractionation of soil P were used to infer P transformations. Soil redox potential (Eh) decreased with flooding and favored reductive dissolution of Fe‐associated P increasing porewater DRP concentrations. Greater solubility of Ca‐P under acidic pH maintained a higher DRP concentration in NBG‐SL during early stages of flooding. A subsequent increase in pH with flooding and higher Ca concentration with added gypsum enhanced the stability of Ca‐P (β‐tricalcium phosphate and octacalcium phosphate), reducing the DRP concentration in gypsum‐amended NBG‐SL. Stability of Ca‐P was less affected with flooding and gypsum amendment in FYL‐Cl soil because it had an alkaline pH and inherently higher Ca concentration. The FYL‐Cl, with a more rapid decrease in Eh than NBG‐SL, became severely reduced, releasing more P and Fe by 70 DAF. These conditions favored vivianite formation in FYL‐Cl but not in NBG‐SL.

Utility of organic carbon (OC) content as an indicator of corn (Zea maize L.) grain yield and yield response to nitrogen (N) across a broad range of conditions was assessed using data from two studies (the first on a variable landscape at Elora Research Station and the second on 19 landscapes in private farms) conducted from 1998 to 2003 in southern Ontario. Zero and 140/150 kg N ha⁻¹ were applied in all studies. Yields generally increased linearly or quadratically with increasing OC. Regression models indicated 42% of the data sets had no response to fertilizer N and in only two data sets in Elora and no data sets in private farms were yield responses to N dependent on OC. When yield increased with fertilizer addition, it was similar for all OC contents in a landscape. We concluded that OC content cannot be used to identify N-management units in southern Ontario.