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.

Ammonia volatilization is one of the major nitrogen loosing pathways in agricultural fields. Particularly, Low-country tea growing areas of Sri Lanka having warm humid climate, often records low or poor responses to current fertilizer recommendations. Therefore, a glasshouse experiment was conducted to determine the gravity of ammonia volatilized from four major tea growing Soil Series of the Low-country wet zone. Air tightened closed chambers with soils containing acid traps were used to quantify ammonia volatilized from applied fertilizers. The experiment was conducted for 100 days while monitoring temperature and relative humidity in the glasshouse which were comparable with prevailing conditions in the low-country wet zone. Volatilized ammonia was quantified daily at the beginning and later with elapsed time. Curves defining the release of ammonia with time and the change of pH with time were plotted from the results. Significant differences were observed in soil pH changes among treatments. Sulphate of ammonia based T1130 mixture recorded the least change in soil pH while urea based VPLC 880 showed the highest variation. During the experimental period, highest pH was recorded at the fourth day after treatment application which confirms the peak hydrolysis of urea. No significant differences were recorded in soil pH changes with soil series. Ammonia volatilization was lowest in T 1130 treatment and it behaved similar to the control treatment without fertilization. Ammonia losses were highest in VPLC 880 fertilizer amounting to 29%. Other urea based mixtures also showed considerably higher losses as U 709-27%, U834-27%, UT 752-26%. T 1130 showed minimum losses as 1% similar to the control. Among soil Series NH 3 losses sequenced as Dodangoda > Weddagala > Malaboda > Pallegoda. As these soils show lower pH buffering ability, split application of urea based fertilizers may effective to minimize said NH 3 losses.

Phosphorus (P) enrichment of soil due to the intensification of P fertilizer usage in crop production has resulted in eutrophication and serious economic consequences. Further, rapidly decreasing P reserves have renewed interest in improving more sustainable soil P management through monitoring diverse soil P reactions in contrasting soils. Therefore, the study was conducted to (i) characterize P sorption and desorption capacities related to soil properties and (ii) determine the added P availability and distribution among the different pools of P over the period concerning P sorption capacity of the soils. Three soils, namely Ultisols, Entisols, and Inceptisols, were equilibrated with a series of P concentrations to study P sorption–desorption using Langmuir isotherms. These soils were subjected to a sequential extraction procedure to study fractions in different pools after incubating with added P for 120 days. Maximum P sorption for Ultisols, Entisols, and Inceptisols were 1,428.6, 1,666.7, and 3,333.3 mg kg⁻¹ soil, respectively. Phosphorus desorption by Ultisol was about 1.7- and 4.2-fold higher than Entisols and Inceptisols. The maximum P sorption showed a negative and significant correlation with soil pH (r = −0.88), whereas P des % has a significant and positive correlation (r = 0.98). Exchangeable Al, Al-ox, Al-cD, and Fe-ox showed a significant positive correlation with maximum P sorption and a negative correlation with P des %. During incubation, 93.3% of added P became non-extractable in Inceptisols, and in contrast only 64.3% for Ultisols. A greater increase in labile NaHCO₃-P fraction was found in Ultisols from 66.96 to 135.6 mg/kg at the end of the incubation. Accordingly, the soils with lower sorption capacity consist of more labile P pools, which indicates a higher risk of the loss of P from the soil.

The rice plant accumulates silicon (Si) in greater quantity, which varies among the rice genotypes. This study was conducted to determine the optimum fertilization rate and its effect on growth, yield, yield attributes, and soil nutrient uptake. Six different silicon dioxide (SiO2) rates, including 0, 50, 75, 100, 125, and 150 kg SiO2/ha, were applied initially. The optimum rate of SiO2 was obtained by statistical analysis, utilizing the analysis of variance (ANOVA) and Duncan's Multiple Range Test (DMRT) to separate the means. The results showed that shoot dry weight and plant height were significantly affected by Si fertilization. The highest Si tissue concentration of 395.27 mu g/100 mg was recorded in 100 kg SiO2/ha treated plants, and their potassium, phosphorous, silicon, and magnesium uptakes were increased by 2, 1.3, 11 and 1.8 folds, respectively. Further, in yield attributes, 32 and 52% increments and a 30% decrease were observed in the total number of grains, filled grains, and unfilled grains per panicle, respectively, and were not significantly different from those observed in 125 kg SiO2/ha rate. The highest grain yield of 104.6 g/pot was obtained with 100 kg SiO2/ha level of Si fertilizer, and it was statistically at par with the yields obtained with 125 kg SiO2/ha. The quadratic function found the rate of Si fertilizer for optimum grain yield (100.5 g/pot) as 115 kg SiO2/ha; thus, it could be concluded that indica rice genotypes need to be fertilized with 115 kg SiO2/ha for optimum yield for higher growth and nutrient uptake.