Soil Water Flow Research Articles

ESTIMATION OF WATER BALANCE UNDER THE CONDITIONS OF CROPS GROWING ON DRY PEAT SOILS OF POLISSІA ZONE

The paper presents the data concerning the researches which point out to the fact that the soil water flow plays an important role in the natural conditions biological complex as well as in the amelioration practice. The intensity of the soil water-intake process has been characterized by its variability and depends on the porousness, mechanical, mineral, chemical composition as well as on itscultivation, soil spaces, cracks, moles, roots and other openings. The water balance of meliorated soils includes some components such as the precipitation, surface and subsurface waters, which comes from he nearest headers, infiltrated rivers and storages lakes waters as well as from condensed waters, transpiration, soil and water surface evaporation in particular. The research of the matter needs the detail scientific substantiation under the conditions of different crops growing on dry soils of Polissya zone. The water balance of cropsgrowing on dry peat soils during the vegetation period for the layer of 0-50 cm has been investigated. The calculations showed that the process of water supply optimization on dry peat soils had an essential effect on its yielding level, herewith the crops efficiency under the regulated and controlled soils water levels increased greatly. Natural LSW comprise to special years as well as to theperiods of plant vegetation. In this case, the methods of moisture intensive management and modelling usage, can supply plant biological necessity under the efficient and qualitative yielding formation. The optimal moisture under the layer of 0-50 cm on dry peat soils during the period of yield forming for the perennial grasses and vetch-oat mixtures made up 77-89%. It has become possible to achieve the highest efficiency of crops green mass due to a givenmoisture parameters.

Land use change drives the spatio-temporal variation of ecosystem services and their interactions along an altitudinal gradient in Brazil

ContextLand use and land cover (LULC) changes may affect the provision of ecosystem services. However, little is known how LULC changes influence the spatio-temporal variation in ecosystem service and their interactions along altitudinal gradients.ObjectivesHere we assessed the spatio-temporal variation of eight ecosystem services in an altitudinal gradient between the year of 1986 and 2015, and quantified the effect of LULC transitions on the provision and interactions of ecosystems services.MethodsWe modelled and mapped eight ecosystem services in an altitudinal gradient characterized by low (< 600 m), middle (600–1200) and high altitudes (> 1200) in Zona da Mata, Minas Gerais state, Brazil. We quantified changes in ecosystem services by contrasting ecosystem service maps between 1986 and 2015, and explored how four common LULC transitions affected the variation and the interactions between the eight ecosystem services.ResultsThe spatio-temporal analysis indicated that six out of eight ecosystem services increased from 1986 to 2015, while soil erosion control and water flow regulation decreased. In areas above 1200 m, regulating services dominated, while in areas below 1200 m provisioning service were most evidenced. LULC transitions from forest to agricultural areas, and vice versa, resulted in trade-offs between provisioning and regulating ecosystem services.ConclusionsLULC changes drive the spatio-temporal variation of ecosystem services along an altitudinal gradient with contrasting biophysical conditions. Future management of ecosystem services in the landscapes should take into the account the biophysical conditions and the consequences of specific LULC transitions.

Analytical Solution of the Richards Equation under Gravity-Driven Infiltration and Constant Rainfall Intensity

In the field of soil hydrology, the Richards equation is commonly used to model water flow in unsaturated soils. The high nonlinearity of the Richards equation makes it very challenging to solve analytically for situations that are meaningful in practical applications. In this paper, an exact and simple analytical solution of the Richards equation under gravity-driven infiltration and constant rainfall intensity is derived. First, the solution is presented under Torricelli’s law, which mimics the soil hydraulic conductivity function and describes the emptying or filling process of a nonlinear water reservoir. Then, following a similar approach, the solution is extended to the Brooks and Corey soil hydraulic conductivity function, which is generally considered to well describe soil hydrological characteristics. The approach followed in this study is a simple hydraulic approach; therefore, the derived solutions are not affected by uncertainty as long as the hypothesis of the gravity-driven infiltration is satisfied for the selected soils. A comparison with the solution numerically derived by the Richards equation for which the gravity-driven assumption is relaxed is performed and discussed. Interestingly, the comparison indicated that the suggested solution delimits the solutions domain of the Richards equation.

Simple functions for describing soil water retention and the unsaturated hydraulic conductivity from saturation to complete dryness

Many applications require accurate soil hydraulic functions that can describe the dynamics of water in variably saturated systems from full saturation to complete dryness. Current functions considering zero water content at the dry end involve the summation of capillary and adsorption functions. This study proposes relatively simple yet complete soil hydraulic functions from full saturation to oven dryness that can be incorporated into existing models. The proposed water retention model is constructed by scaling the saturation function of Fredlund and Xing (1994) to describe capillary and adsorptive water retention as well as zero water content at oven dryness. To describe the hydraulic conductivity due to capillary and film flow, the model of Wang et al. (2018) is used. We further incorporated hysteresis in the water retention function of Wang et al. (2018). Testing on 241 hydraulic property data sets covering a wide range of soil textures from sands to clays, shows good agreement with laboratory observations, especially for coarse-textured soils. The proposed model accounts for the following processes: hysteretic capillary and adsorptive water retention, hysteretic hydraulic conductivity as a function of pressure head, non-hysteretic hydraulic conductivity as a function of water content, the effects of entrapped air, and closed scanning curves. This paper successfully derives the parameters of the main wetting curve from the main drying curve. Using the proposed functions for soil water flow modelling should lead to improved dynamic flow predictions, especially for drying soil conditions.

Homogenization of Dissolution and Enhanced Precipitation Induced by Bubbles in Multiphase Flow Systems

AbstractMultiphase flow is ubiquitous in subsurface energy applications and natural processes, such as oil recovery, CO2 sequestration, and water flow in soils. Despite its importance, we still lack a thorough understanding of the coupling of multiphase flow and reaction of transported fluids with the confining media, including rock dissolution and mineral precipitation. Through the use of geomaterial microfluidic flow experiments and high‐performance computer simulations, we identify key pore‐scale mechanisms that control this coupling. We compare the reactivity of fractured limestone with CO2‐saturated brine (single phase) and a mixture of supercritical (sc) CO2 and CO2‐saturated brine (multiphase). We find that the presence of scCO2 bubbles significantly changes both the flow dynamics and the resulting reaction patterns from a single‐phase system, spatially homogenizing the rock dissolution. In addition, bubbles redirect oversaturated fluid into low‐velocity regions, thereby enhancing carbonate precipitation occurs.

Call for Participation: Collaborative Benchmarking of Functional-Structural Root Architecture Models. The Case of Root Water Uptake.

Three-dimensional models of root growth, architecture and function are becoming important tools that aid the design of agricultural management schemes and the selection of beneficial root traits. However, while benchmarking is common in many disciplines that use numerical models, such as natural and engineering sciences, functional-structural root architecture models have never been systematically compared. The following reasons might induce disagreement between the simulation results of different models: different representation of root growth, sink term of root water and solute uptake and representation of the rhizosphere. Presently, the extent of discrepancies is unknown, and a framework for quantitatively comparing functional-structural root architecture models is required. We propose, in a first step, to define benchmarking scenarios that test individual components of complex models: root architecture, water flow in soil and water flow in roots. While the latter two will focus mainly on comparing numerical aspects, the root architectural models have to be compared at a conceptual level as they generally differ in process representation. Therefore, defining common inputs that allow recreating reference root systems in all models will be a key challenge. In a second step, benchmarking scenarios for the coupled problems are defined. We expect that the results of step 1 will enable us to better interpret differences found in step 2. This benchmarking will result in a better understanding of the different models and contribute toward improving them. Improved models will allow us to simulate various scenarios with greater confidence and avoid bugs, numerical errors or conceptual misunderstandings. This work will set a standard for future model development.

Recognizing the role of plant species composition in the modification of soil nutrients and water in rubber agroforestry systems

Reliable guidance for crop selection and related management to achieve sustainable soil resource use in rubber agroforestry systems is limited. One important reason for this limited guidance is that our understanding of the effects of different plant functional groups on soil resources is still insufficient. Here, to examine the effects of the species composition of trees, shrubs and herbs on soil nutrients and soil water with increases in the complexity of the plant community structure, we measured the soil nutrient concentrations (i.e., C, N, P, K, Ca and Mg), soil water content and soil water residence time (with stable hydrogen and oxygen isotope tracers) at six soil depths in a monoculture rubber plantation, four multi-species rubber agroforestry systems, and a tropical rainforest. As the plant species composition increased, the soil C and N increased. The soil water content also increased with increases in soil C and N. However, the effects of plant species composition on the soil water content gradually changed from positive to negative, especially under the effects of herb species, which could accelerate soil water drainage and hence shorten the soil water residence time. Therefore, the faster water infiltration and potentially higher flow of soil water in complex plant communities increased the risk and magnitude of mineral nutrient leaching. In addition, as the plant composition increased, plant competition decreased the concentration of soil nutrients, especially soil P, K and Ca. In general, plant interspecific interactions definitively decreased soil mineral nutrients as the plant composition increased, and the effects of tree, shrub and herb species on soil nutrients and soil water differed and sometimes appeared contradictory. However, the effects of plant species composition on soil gradually weakened with increases in soil depth.

Probabilistic characterization of the soil-water retention curve and hydraulic conductivity and its application to slope reliability analysis

Abstract Soil-water retention curve (SWRC) and hydraulic conductivity are two indispensable inputs in unsaturated seepage analysis for analyzing water flow in unsaturated soils, which can be obtained through direct measurements. Generally, the test data of the SWRC and unsaturated hydraulic conductivity obtained from direct measurements are limited because such measurements are time-consuming and costly. Thus, it is hard to determine an SWRC and hydraulic conductivity with certainty from a probabilistic perspective. How to quantify the uncertainty in them remains an unresolved question. This paper aims to propose a Bayesian approach to characterize the SWRC and hydraulic conductivity. The proposed approach is illustrated through a slope example. Results show that the proposed Bayesian approach is not only able to quantify the uncertainty in the estimated SWRC and hydraulic conductivity, but also capable of predicting the SWRC and hydraulic conductivity with reasonable accuracy. This facilitates the determination of both the SWRC and hydraulic conductivity in geotechnical applications for engineers by making use of the available test data. Moreover, the proposed approach offers a viable way to provide a robust estimate of slope failure probability by virtue of Bayesian model averaging, allowing SWRC parameter uncertainty and model selection uncertainty to be considered simultaneously in reliability analysis. This addresses the dilemma of over-reliance on a single SWRC model in geotechnical reliability analysis involving unsaturated soils. It is worthy to note that among the four candidate models, three of them belong to one category which may have similar abilities, other parametric models in different categories need to be considered in future research.

Can complementary preferential flow and non-preferential flow domains contribute to soil water supply for rubber plantation?

Preferential flow has always been hotspot of research regarding soil water flow, biological activity, and carbon and nitrogen dynamics. However, the mechanism of water flow exchange between two adjacent zones (with and without root system) and the pattern of soil water supply for rubber are still unclear. In the present study, we considered two plots experiencing similar farming history: in the first plot we measured soil physical properties and soil volumetric water content (VWC) during rainfall, and the second plot was used to visualise water flow path and to measure root biomass. Besides, a model was developed on preferential flow domain (PFD, matching the root zone) and on non-preferential flow domain (NPFD, matching the remote root zone) to compute differences in soil properties between the PFD and NPFD. The results revealed that the dominant flow type in the PFD was preferential flow and the one in the NPFD was capillary flow. Dye stained area and wetting front rate negatively correlated with bulk density, while they positively correlated to non-capillary porosity and root biomass. Accordingly, PFD showed a quick response to rainfall. Indeed, during the rain, a lateral flow (driven by water gravity and pressure head gradient) predominantly carried water (0.95, 0.27, and 0.44 cm3 cm−3 for various rainfall events 1, 2, and 3, respectively) from PFD to NPFD. During the soil drainage stage, the lateral flow direction changed, and water (about 0.63, 0.30, and 0.39 cm3 cm−3 for rainfall events 1, 2, and 3, respectively) flowed from NPFD to PFD. As a result, PFD presented low storage and high flow characteristics compared with NPFD, suggesting this complementary relationship for water interaction between the two domains could be beneficial for rubber plants growth and development.

Viscosity Controls Rapid Infiltration and Drainage, Not the Macropores

The paper argues that universal approaches to infiltration and drainage in permeable media pivoting around capillarity and leading to dual porosity, non-equilibrium, or preferential flow need to be replaced by a dual process approach. One process has to account for relatively fast infiltration and drainage based on Newton’s viscous shear flow, while the other one draws from capillarity and is responsible for storage and relatively slow redistribution of soil water. Already in the second half of the 19th Century were two separate processes postulated, however, Buckingham’s and Richards’ apparent universal capillarity-based approaches to the flow and storage of water in soils dominated. The paper introduces the basics of Newton’s shear flow in permeable media. It then presents experimental applications, and explores the relationships of Newton’s shear flow with Darcy’s law, Forchheimer’s and Richards’ equations, and finally extends to the transport of solutes and particles.

Linear relation between leaf xylem water potential and transpiration in pearl millet during soil drying

As soil dries, the loss of soil hydraulic conductivity limits water supply to the leaves, which is expected to generate a nonlinear relationship between leaf water potential (ψleaf) and transpiration (E). The effect of soil drying and root properties on ψleaf and E remains elusive. We measured E and ψleaf of pearl millet for varying E and soil moisture using a root pressure chamber. A model of water flow in soil and plant was used to fit the ψleaf (E) relationship. The relation between ψleaf and E was linear at all soil moistures. The slope of ψleaf (E) increased with decreasing soil moisture due to the decreasing soil-root conductance. The fact that the relation remained linear also in dry soils and high E is surprising. Indeed, it indicates that the gradients in soil water potential (ψsoil) were small, probably because of the large root surface (13.5 cm cm−3) active in water uptake. ψleaf at E = 0 was less negative than ψsoil, indicating a more negative osmotic potential in the xylem than in the soil. We propose that the linearity between ψleaf and E and the high ψleaf (E = 0) compared to ψsoil support transpiration in drying soils.

Modeling and comparative analysis of a flow and heat coupling model of the riparian zone based on thermal conductivity empirical models

Recently, the use of heat as a tracer to evaluate the process of hyporheic exchange in riparian zones has attracted wide attention. A more accurate flow-heat coupling model of riparian zones could help us understand the patterns of water flow and heat transfer in riparian zones and provide a scientific basis for the comprehensive management and efficient utilization of these zones. In this paper, a flow-heat coupling model of a riparian zone based on thermal conductivity empirical models (TCEMs) was built by customizing partial differential equations (PDEs) based on the simulation of soil water flow using porous media and the subsurface flow module in COMSOL. Combined with the data collected from the field heat tracer test in the riparian zone, the flow-heat coupling model of the riparian zone under 12 types of TCEMs was validated and compared. The results show that the use of the PDE module instead of the heat transfer in porous media (HTPM) module is very effective for modeling; the PDE module could basically replace the HTPM module in the heat transfer calculation. The performance of the flow-heat coupling model varies under different types of TCEMs, and the Chung and Horton (1987) model shows better simulation effects, with a root mean square error (RMSE), coefficient of determination (R2), mean absolute error (MAE), and mean relative error (MRE) ranging from 1.37 to 2.48 ℃, 0.73–0.94, 1.06–2.08 ℃, and 11.94–15.79%, respectively. Therefore, this model could better reflect the dynamic temperature variations in the riparian zone. The sensitivity analysis results illustrate that the hydraulic conductivity (Ks), van Genuchten parameter (β), volumetric heat capacity of dry solids (Cs), and porosity (n) of the flow-heat coupling model greatly influence riparian zone temperature variations, and the parameters β, Ks, and residual water content (θr) significantly affect the lateral hyporheic exchange rate in the riparian zone, of which β has the largest effect.

Measurement of xylem water pressure using High-Capacity Tensiometer and benchmarking against Pressure Chamber and Thermocouple Psychrometer

The response of the shallow portion of the ground (vadose zone) and of earth structures is affected by the interaction with the atmosphere. Rainwater infiltration and evapotranspiration affect the stability of man-made and natural slopes and cause shallow foundations and embankments to settle and heave. Very frequently, the ground surface is covered by vegetation and, as a result, transpiration plays a major role in ground-atmosphere interaction. The soil, the plant, and the atmosphere form a continuous hydraulic system, which is referred to as Soil-Plant-Atmosphere Continuum (SPAC). The SPAC actually represents the ‘boundary condition’ of the geotechnical water flow problem. Water flow in soil and plant takes place because of gradients in hydraulic head triggered by the negative water pressure (water tension) generated in the leaf stomata. To study the response of the SPAC, (negative) water pressure needs to be measured not only in the soil but also in the plant. The paper presents a novel technique to measure the xylem water pressure based on the use of the High-Capacity Tensiometer (HCT), which is benchmarked against conventional techniques for xylem water pressure measurements, i.e. the Pressure Chamber (PC) and the Thermocouple Psychrometer (TP).

Impacts of Unsaturated Conditions on The Ultimate Axial Capacity of Energy Piles

This study uses concepts from unsaturated soil mechanics to explain changes in axial capacity observed in geotechnical centrifuge experiments on semi-floating energy piles in unsaturated silt heated monotonically to different temperatures. Thermally-induced drying of the unsaturated silt surrounding energy piles was observed during heating using temperature-corrected dielectric sensor readings. An effective stress-based equation for estimating the ultimate capacity was calibrated using the load-settlement curves for a pile at room-temperature, which was then used to estimate the ultimate capacities of energy piles under elevated temperatures using measured changes in degree of saturation near the energy pile. The predicted capacity matched well with the capacity from the experimental load-settlement curves, confirming the relevance of the effective stress principle in unsaturated soils in nonisothermal conditions and the importance of considering coupled heat transfer and water flow in unsaturated soils surrounding energy piles.

Rock outcrops change infiltrability and water flow behavior in a karst soil

AbstractRock outcrops are widespread across the surface of the earth, particularly in karst environments, and they play an important role in infiltration‐runoff processes by triggering preferential flow. However, the characteristics of the preferential flow network at the soil–rock interface and its influencing factors in karst areas remain poorly understood. To clarify how the emergence of outcrops on the land surface affects soil infiltrability and water flow behavior, soil hydraulic conductivity (K) measurements and dye tracing experiments were conducted in a karst area with two contrasting surface features (i.e., rock outcrop plot [RP] and non‐rock‐outcrop plot [NRP]) in Yunnan Province, Southwest China. Results showed that (i) in the immediate vicinity of rock outcrops in the RP, K values were significantly increased, and other soil properties and plants were also improved when compared with results 1 m away from outcrops and in the NRP; and (ii) in the RP, the soil–rock interface dominated the preferential flow network surrounding outcrops, and the connected conduits produced by plant roots and soil fauna were also involved in this infiltration process. Matrix flow was the dominant flow behavior in the NRP. We concluded that rock outcrops, by improving soil properties and building a well‐connected preferential flow network, can greatly change infiltrability and water flow behavior in karst soil. This implied that outcrops will facilitate quick infiltration after most rainfall events and thus reduce rain‐induced surface runoff and soil erosion, as well as increasing groundwater recharge and the water supply to nearby plants.

Soil water flow due to surface topography in research drainage plots

AbstractTile drainage is common in the central United States and has resulted in greater storm flashiness. The purpose of this study was to determine if surface topography influenced water table depths, tile outflow, and water flow patterns in experimental plots. Tiles (1.22‐m deep) were installed at the center of each plot, and plastic barriers (1.83‐m deep) were installed between plots. Monitoring wells were installed and were read monthly during the growing season. During times with little rain the well‐drained block had the deepest water table depths (maximum of 4.75 m), and the wettest block had the shallowest water table depths (maximum of 2.15 m). During times with much rain, water table depths were similar for all blocks; however, water table gradients were larger during wet periods than dry periods (for example, 3.0 m m−1 vs. 0.5 m m−1). Mean water table depths for the well‐drained block were below the plastic barrier 47% of the time and below the tile depth 72% of the time. Conversely mean water table depths for the wettest block were deeper than the plastic barrier only 18% of the time and below the tile 54% of the time. There was slow lateral flow below the barriers from the upslope block to downslope plots; some downslope plots still had tile flow when there was lateral flow from upslope.

Influence of exchangeable sodium and clay mineralogy on soil water retention and hydraulic conductivity

Soil hydraulic properties are important for water management in salt and sodium (Na) affected soils. The soil saturated hydraulic conductivity (K_sat) has been found to decrease when high soil solution Na adsorption ratio (SAR) is coupled with low solution electrical conductivity (EC). Soil clay type plays an important role in changes to soil K_sat when the soil solution composition has a high SAR and low EC. Little is known about how soil water retention changes from solution EC and SAR. The objective of this study was to determine the impact of a range of solution EC and SAR values on soil K_sat, and water retention for soils containing swelling and nonswelling clay minerals. The soil K_sat and water retention were measured on four smectitic soils, a kaolinitic soil, and an illitic soil. Smectite swelling caused large changes in soil hydraulic properties in smectitic soils at high exchangeable Na percentage (ESP) and low EC levels, whereas there was a reduced effect on soils with little smectite clay. Increasing soil solution ESP and decreasing EC level caused the K_sat to decrease and the water content at a given pressure head to increase on soils that contained smectite. A narrower range of EC and SAR of waters suitable for use on smectitic soils are required to prevent changes in soil water flow rates and soil water retention.

Parallel simulation of variably saturated soil water flows by fully implicit domain decomposition methods

The growing complexity of geometric models for the simulation of subsurface flows leads to the necessity of using the fully implicit method, due to its unconditionally stability with the relaxation of the time step size. In the paper, we introduce and study a parallel and scalable fully implicit solver for the simulation of variably saturated soil water flows. In the proposed approach, the flow problem is discretized in space and time based on a fully implicit, cell-centered finite volume scheme, where several different limiters are applied to guarantee the accuracy of the spatial discretization and an adaptive time-stepping technique for the temporal integration is designed to accelerate the simulation progress. And then the resultant nonlinear algebraic system, arising from the discretization of the variably saturated soil water flows, is solved by a family of Newton–Krylov methods under the domain decomposition framework. Numerical experiments on several standard benchmark tests are used to validate the stability of the fully implicit scheme with large time steps, and to examine the performance of the proposed domain decomposition solver on a parallel computer platform.

A new kinematic–dispersive wave van Genuchten (KDW-VG) model for numerical simulation of preferential water flow in soil

Preferential water flow in soil macropores such as underground channels formed by worm activity and plant root growth, can move a large volume of water and contaminants to groundwater resources in a short time. To describe these types of water flow in soil, Di Pietro et al. (2003) developed and proposed kinematic–dispersive wave (KDW) model. They suggested this model by adding a dispersive term to the kinematic wave (KW) model that was severely convective and was presented by Germann in 1985. The fundamental assumption of this model is that the water flux (u) is exclusively a function of the mobile water content, but in the KDW model, considering its additional dispersive term, it is assumed that the water flux is a non-linear function of the mobile water content and its first-time derivative. The first term of this assumption is a power function where the water flux depends on the mobile water content. This equation is just a mathematical equation and has no significant physical meaning. In this research, this power function is substituted by the shape of van Genuchten model that has an acceptable physical meaning, and thus the kinematic–dispersive wave van Genuchten (KDW-VG) model is introduced for the first time as the innovation of this research. The models were calibrated and validated with observations of four different rainfall intensities that were applied on the surface of a soil column with artificial preferential pathways. The output water fluxes from the bottom of the soil column versus the soil mobile volumetric water content in the column were recorded at set times. First, both the KDW and KDW-VG models were calibrated and their indefinite coefficients were determined by minimizing the error function between the observed and modelled water fluxes versus mobile volumetric water content using particle swarm optimization (PSO) algorithm. Next, both models, which are second-degree non-linear partial differential equations, were solved using numerical finite difference method with the MATLAB programming language, and were validated by experimental observations of rainfall hydrograph that was passed through the preferential routes of a physical model and was recorded from the bottom of the soil column. Root-mean-square error (RMSE) comparison of the models predictions and observations indicated that the proposed model (KDW-VG) could predict the observations more accurately compared with the KDW model, and also had better performance in the calibration stage.

Improving Nitrogen Availability on a Tropical Peat Soil Cultivated with Ananas comosus L. Merr. Using Pineapple Residue Ash

The objectives of this study were to use pineapple residue ash to (i) reduce ammonium and nitrate leaching and (ii) improve essential nutrient availability on a tropical peat soil under pineapple cultivation. Laboratory leaching experiments were carried out to determine the effectiveness of pineapple residue ash in controlling nitrogen loss from a tropical peat soil. Ion exchange resin method was used to determine nitrogen availability. Treatments evaluated were (i) different amounts of pineapple residue ash (25, 50, 70, and 100%) + NPK fertilizer, (ii) NPK fertilizer, and (iii) peat soil alone. Peat soils with pineapple residue ash reduced ammonium and nitrate losses because of adsorption of ammonium and nitrate by hydroxyl and C–O radicals of the pineapple residue ash. There was an improvement in ammonium and nitrate availability because the pineapple residue ash was able to increase the peat soil pH and this facilitated organic nitrogen mineralization and nitrification. The pineapple residue ash also improved nitrogen uptake, pineapple fresh fruit yield, and fruit quality. Ammonium and nitrate varied with soil depth because of high preferential flow of the peat soil water. Combined use of NPK fertilizers and 25% pineapple residue ash improved nitrogen availability whereas amending NPK with 50%, 70%, and 100% pineapple residue ash were more effective in improving nitrogen uptake, fresh fruit yield, and fruit quality of pineapple. Pineapple residue ash can also have significant liming effect.