Potassium Release from Biomass Particles during Combustion—Real-Time In Situ TDLAS Detection and Numerical Simulation

Potassium (K) is one of the main and most hazardous trace species released to the gas-phase during thermochemical conversion of biomass. Accurate experimental data and models of K release are needed to better understand the chemistry involved. Tunable diode laser absorption spectroscopy (TDLAS) is used for simultaneous real-time in situ measurements of gas-phase atomic K, water (H2O) and gas temperature in the vicinity (boundary layer) of biomass particles during combustion in a laboratory single-particle reactor. Atomic K is detected in a wide dynamic range, including optically thick conditions, using direct absorption spectroscopy at the wavelength of 770 nm, while H2O and temperature are determined by calibration-free scanned wavelength modulation spectroscopy at 1398 nm. The high accuracy and repeatability of the setup allows to distinguish measurements with varying initial particle mass, laser beam height above the particle and fuel type. Four types of biomass with different ash composition are investigated: softwood, Salix, Miscanthus and wheat straw. For Salix and wheat straw, the K release behaviour is, for the first time, compared to a detailed numerical particle model taking into account the interaction between K/S/Cl composition in the particle ash. A good agreement is achieved between the measured and calculated time-resolved atomic K concentrations for the devolatilization phase of the biomass particles.

Kinetics of potassium release from soil amended with clinoptilolite zeolite and maize stalks biochar

A laboratory incubation experiment in a completely randomized design with three replications was carried out for 90 days to test the effect of zeolite and biochar application to calcareous sandy loam soil on potassium forms distribution and its release rate. The treatments included (1) Absolute control (C), (2) 10 g kg-1 zeolite (Z1), (3) 20 g kg-1 zeolite (Z2), (4) 10 g kg-1 biochar (B1), and (5) 20 g kg-1 biochar (B2). After incubation period, the concentrations of soluble, exchangeable, and non-exchangeable K and the release rate of K to 0.01 M CaCl2 during 200 min (10 successive extractions for soil samples of 20 min for each using CaCl2 solution) were determined. Results showed that zeolite application increased the soluble and exchangeable K concentrations. However, amending soil with biochar had a positive effect on all K forms. Addition of zeolite or biochar increased the cumulative K release. The parabolic diffusion, power function and Simple Elovich models described the kinetics of K release to CaCl2 solution well from all the soil treatments. Zeolite and maize stalks biochar may have an effective role in improvement of K availability and release in the calcareous sandy loam soil as well as may aid in increasing the ability of this soil to supply the different crops with K.

Effect of Rice Straw on Potassium Availability in Illite Containing Soils of Central Plain, Thailand

Soil potassium (K) in various forms and the effect of rice straw on soil K release were studied in lowland soils containing illite clay minerals. Surface soils of 2 Inceptisols and 2 Alfisols were collected to study. Soil samples were incubated for 120 days with rice straw incorporation at different rates (0, 3,125, 6,250, and 9,375 kg/ha), and various forms of K in soils were determined at various times during the period of incubation. The results showed that the readily available K content (water-soluble K + exchangeable K) of the studied soils increased with the increasing rate of rice straw incorporation. In addition, non-exchangeable K content also increased with the increasing rate of rice straw incorporation by fixation process for all soils. The maximum increase of water-soluble K content of the studied soils was observed on the 4th day of incubation for all treatments, corresponding to the decrease of exchangeable K content at the same time. This result indicated that water-soluble K and exchangeable K were in equilibrium. Changes of non-exchangeable K content during the period of incubation through alternate release and fixation processes were observed monthly. This result suggested that most of the readily available K enhanced by rice straw incorporation would be beneficial for K uptake by the plant.

Sheep Dung Composition and Phosphorus and Potassium Release Affected by Grazing Intensity and Pasture Development Stage in an Integrated Crop-Livestock System

Animal grazing in integrated crop-livestock systems (ICLS) results in continuous nutrient release to forage plants and crops in succession. This study aimed to assess sheep dung composition and decomposition rates under distinct grazing intensities and at different development stages of Italian ryegrass pasture (Lolium multiflorum Lam.), and to evaluate dung phosphorus (P) and potassium (K) release dynamics during two annual ICLS cycles (2015 and 2016) in southern Brazil. Treatments consisted of two grazing intensities (moderate and light) and two pasture development stages (vegetative and post-flowering), arranged in a randomized complete block design with split-split-plots and four replicates. Dry matter (DM) decomposition and P and K release rates were determined using litter bags with sheep dung. Grazing intensity did not affect sheep dung composition. Forage consumed at different development stages altered sheep dung composition, decomposition, and P and K release rates. Dung sampled at pasture vegetative stage showed P and K contents 16% and 7% higher, respectively, than dung from the post-flowering stage. Dung collected at pasture post-flowering stage had 26% more cellulose and 34% more hemicellulose compared to dung from the vegetative stage in 2016. P and K release was greater for dung from pasture vegetative stage, reaching 3.7 and 12.9 kg ha−1 of P and K, respectively. Further evaluations are still needed considering the quantification and release of nutrients in each of the different compartments (pasture, urine, and dung residues) that compose the system.

Dry matter decomposition and potassium cycling in no-till integrated crop-livestock systems: the effects of tree shading and nitrogen fertilization

In integrated crop-livestock systems (ICLS), understanding residue dynamics is crucial to synchronize nutrient release from pasture litter to cash-crop nutrient demands and overcome potential deficiencies using suitable fertilization strategies. The present study evaluated how the inclusion of trees and N availability affected the release rates of K from pasture (black oat + ryegrass) residues to the subsequent maize crop in a no-till ICLS. The experimental design was randomized blocks with treatments set up in split-plots with three replications. Main plots were systems (crop-livestock only and crop-livestock with trees) and sub-plots N levels (90 and 180 kg N ha-1). Litter decomposition and K release from pasture residues were assessed using litterbags, which were installed at maize sowing, for retrieval at 8, 15, 30, 60, 90, 120, 150, and 165 days of incubation. Regardless of N level, shade of 7-year-old trees reduced pasture residue (-30%). Tree residues were unable to offset the shading effect on pasture growth. A faster dry matter decomposition was observed in treeless treatment and with 180 kg N ha-1, with a half-life ranging from 14 to 38 days. Despite no changes in K-release dynamics among treatments, total K released was significantly higher for treeless system (61 kg K ha-1) than in system with trees (40 kg K ha-1), due to changes in the initial amount of residue. These results must be taken into account in fertilization practices. Therefore, a few feasible silvicultural interventions should be considered to avoid losses in soil cover, maximizing nutrient cycling benefits.