Liming Effects on Nitrate Adsorption in Soils With Variable Charge Clays and Implications for Ground Water Contamination

The present research sought to determine the extent and distribution of nitrate accumulation in the subsoils of central Oahu, and to measure the consequences of surface applied amendments on nitrate mobility. Deep bore holes collected from pineapple fields in central Oahu were analyzed for nitrate and nitrate adsorption, and a lime incubation experiment and column study were conducted. Three and one half to 11 T/ha of nitrate-N have been measured in subsoils and the deep. saprolitic vadose zones of pineapple fields located in central Oahu, Hawai’i. Nitrate adsorption isotherms confirmed the high nitrate retention capacity of the materials in the subsoil and saprolite. Since large areas of former sugarcane land are being converted to diversified crops requiring amendments to reduce acidity, a lime incubation study was conducted on soils from former sugarcane land to investigate the effect of lime on nitrate adsorption. When lime was added to acid subsoils, nitrate retention was decreased by up to one half of the native adsorption capacity. A leaching experiment found that surface applied lime and gypsum increased nitrate mobility through soil columns 50 cm in length. The data indicate that large quantities of nitrate have accumulated in the subsoil overlying the Pearl Harbor aquifer. Mobility of nitrate through the subsoil is retarded, but a laboratory column study shows that nitrate mobility can be increased by adding lime and gypsum to the surface soil. Field studies need to be conducted to evaluate the potential for ground water contamination as a result of surface applied amendments

Acidification of Volcanic Ash Soils from Maui and Hawai‘i Island for Blueberry and Tea Production

This publication provides background on soil acidity in relation to plant growth, presents approaches to acidifying soils, and provides guidelines for the acidification of some volcanic soils on Maui and Hawai‘i island that are potential sites for tea and blueberry production

Edaphic controls of soil organic carbon in tropical agricultural landscapes

Predicting soil organic carbon (SOC) is problematic in tropical soils because mechanisms of SOC (de)stabilization are not resolved. We aimed to identify such storage mechanisms in a tropical soil landscape constrained by 100 years of similar soil inputs and agricultural disturbance under the production of sugarcane, a C-4 grass and bioenergy feedstock. We measured soil physicochemical parameters, SOC concentration, and SOC dynamics by soil horizon to one meter to identify soil parameters that can predict SOC outcomes. Applying correlative analyses, linear mixed model (LMM) regression, model selection by AICc, and hierarchical clustering we found that slow moving SOC was related to many soil parameters, while the fastest moving SOC was only related to soil surface charge. Our models explained 78-79%, 51-57%, 7-8% of variance in SOC concentration, slow pool decay, and fast pool decay, respectively. Top SOC predictors were roots, the ratio of organo-complexed iron (Fe) to aluminum (Al), water stable aggregates (WSagg), and cation exchange capacity (CEC). Using hierarchical clustering we also assessed SOC predictors across gradients of depth and rainfall with strong reductions in Roots, SOC, and slow pool decay associated with increasing depth, while increased rainfall was associated with increased Clay and WSagg and reduced CEC in surface soils. Increased negative surface charge, water stable aggregation, organo-Fe complexation, and root inputs were key SOC protection mechanisms despite high soil disturbance. Further development of these relationships is expected to improve understanding of SOC storage mechanisms and outcomes in similar tropical agricultural soils globally

Biochar Volatile Matter and Feedstock Effects on Soil Nitrogen Mineralization and Soil Fungal Colonization

Biochar has important biogeochemical functions in soil—first as a means to sequester carbon, and second as a soil conditioner to potentially enhance soil quality and fertility. Volatile matter (VM) content is a property of biochar that describes its degree of thermal alteration, which can have a direct influence on carbon and nitrogen dynamics in soil. In this study, we characterized the VM in biochars derived from two locally sourced feedstocks (corncob and kiawe wood) and evaluated the relationship of VM content to nitrogen transformations and culturable fungal biomass. Using 13C nuclear magnetic resonance (NMR) spectroscopy, we found that the VM content of biochar primarily consisted of alkyl (5.1–10.1%), oxygen-substituted alkyl (2.2–6.7%), and phenolic carbon (9.4–11.6%). In a series of laboratory incubations, we demonstrated that corncob biochars with high VM (23%) content provide a source of bioavailable carbon that appeared to support enhanced viable, culturable fungi (up to 8 fold increase) and cause nitrogen immobilization in the short-term. Corncob biochar with bioavailable VM was nitrogen-limited, and the addition of nitrogen fertilizer resulted in a four-fold increase in total hydrolytic enzyme activity and the abundance of culturable fungal colonies. In contrast, kiawe biochar with an equivalent VM content differed substantially in its composition and effect on these same biological parameters. Therefore, the rapid measurement of VM content is too coarse to differentiate chemical composition and to predict the behavior of biochars across feedstocks and production methods

Response of selected soil physical and hydrologic properties to manure amendment rates, levels, andtypes

Manure amendments affect several soil physical and hydrologic properties. The objectives of this study were to evaluate the effect of (i) manure amendment rates (0, 168, 336, and 672 kg total N ha), levels (one-time application, and two-time application), and types (chicken manure [CM], dairy manure [DM], and swine manure [SM]) on bulk density (ρb), total soil porosity (θt), and saturated hydraulic conductivity (Ksat) of a highly weathered tropical soil (Waialua gravely clay variant, isohyperthermic Pachic Haplustolls) and (ii) measuring instruments (tension infiltrometer [TI] and double-ring infiltrometers [DR]) on Ksat. For the two-time application level, all the plots received additional manure to compensate for the amounts decomposed during the first growing season. The field was tilled to the top 15-cm depth before and after manure application during the two growing seasons. Measurements of ρb and θt were conducted on undisturbed soil core samples collected from the top 10 cm of soil from a field cultivated with sweet corn (Zea mays L. subsp. mays) and irrigated with a drip irrigation system for two consecutive growing seasons. Saturated hydraulic conductivity was calculated from steady state infiltration rates measured with TI and DR. Results show that the increased manure amendment rates and levels significantly (P \u3c 0.01) decreased ρb and consequently increased θt. The values of Ksat increased significantly (P \u3c 0.01) with increase in CM and DM amendment rates and levels. For SM treatments, the values of Ksat decreased with increase in manure amendment rates and levels; these results concur with those reported in literature on liquid manures. Saturated hydraulic conductivity calculated from DR data was slightly greater than that from TI data for CM and DM treatments. Opposite results were found for SM treatments. However, a good agreement (R = 0.90) was observed between Ksat values calculated from TI and DR data across treatments. We conclude that the CM and DM amendments increased θt and Ksat and may also temporarily improve soil aggregation; however, SM amendments result in decreased Ksat. Thus, it is not recommended that slurry SM be applied to the soils with low hydraulic conductivity because it could further inhibit water infiltration and increase surface runoff and soil erosion. © 2008 ippincott Williams & Wilkins

Nutrient concentrations within and below root zones from applied chicken manure in selected Hawaiian soils

The objective of this study was to evaluate the effects of chicken manure (CM) application rates on nutrient concentrations within and below the root zone of sweet corn (Zea mays L. subsp. mays) under Hawaiian conditions. The research was conducted in leeward (Poamoho) and windward (Waimanalo) areas of Oahu, Hawaii, where contrasts exist in both climatic and soil conditions. Suction cup were used to collect soil solutions from 30 and 60 cm depths. Soil solutions were collected six times during the growing season at each location and analyzed for different nutrients (N, P, K, Ca, Mg, Na, Fe, Mn, Zn, and Cu), nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), electrical conductivity (EC), and pH. Analysis showed that CM rates significantly affected the concentration of macro-nutrients below the root zone at Poamoho and within the root zone at Waimanalo. In general, nutrient concentration increased with the increasing rates of CM application. There was a significant effect of CM on micro-nutrients except below the root zone at Poamoho. CM significantly affected NO3-N concentration within the root zone for 15, 60 days after planting (DAP) at Poamoho, and 16, 28 DAP at Waimanalo. The effect was also significant on total nitrogen (N) concentration in the root zone across the two growing seasons at Waimanalo. There was a highly significant correlation between total N and NO3-N, and EC within and below the root zone. © Taylor & Francis Group, LLC

Assessing the Effects of Digestates and Combinations of Digestates and Fertilizer on Yield and Nutrient Use of Brassica juncea (Kai Choy)

Anaerobic digestion of organic wastes produces solid residues known as digestates, which have potential as a fertilizer and soil amendment. The majority of research on digestate focuses on their fertilizer value. However, there is a lack of information about additional effects they may have on plant growth, both positive and negative. Understanding the effects of digestate on plant growth is essential to optimizing their use in agriculture and helping close the loop of material and energy balances. This greenhouse study evaluated the effects of two different digestates, a food waste digestate (FWD) and a lignocellulosic biomass digestate (LBD); a liquid fertilizer; and various combinations of fertilizer and digestates on plant growth, nutrient uptake and nutrient use efficiency (NUE) of Brassica juncea (kai choy) plants. It also evaluated potential negative attributes of the digestates, including salinity and possible biohazards. Combinations of LBD and fertilizer performed as well or slightly better than the fertilizer control for most parameters, including aboveground biomass and root length. These same combinations had significantly higher nitrogen use efficiency than the fertilizer control. Inhibitory effects were observed in 100% LBD treatments, likely due to the high electrical conductivity of the media from digestate application. Based on this research, LBD could partially replace mineral fertilizers for kai choy at up to 50% of the target nitrogen rate and may lead to increased plant growth beyond mineral fertilizers. FWD could replace up to 100% of the target nitrogen application, without causing significant negative effects on plant growth. Increasing the use of digestates in agriculture will provide additional incentives for the anaerobic digestion process, as it produces two valuable products: biogas for energy and digestate for fertilizer

DataSheet1_The legacy of intensive agricultural history on the soil health of (sub)tropical landscapes.pdf

Soil health conceptualized as a measurable ecosystem property provides a powerful tool for monitoring progress in restoration projects or implementation of best management practices to improve degraded lands and promote sustainable agroecosystems. We surveyed soils collected from a range of land uses (i.e., protected native and non-native forest, managed pasture, unmanaged previously intensive agricultural lands, organic cropland, and conventional cropland) across a range of soil orders (Oxisol, Mollisol, Andisol, Inceptisol, and Vertisol) on three Hawaiian Islands. Forty-six soil health indicators encompassing biological, chemical, and physical properties were measured. In this multivariate survey, the most distinct group was the unmanaged, previously intensive agriculture lands, which was significantly different from all other land uses even when considering differences in mineralogy. Importantly, the soil health indicators of well-managed pastures in Hawaiʻi were not different from protected forests, suggesting that well-managed grazing lands may be as healthy and resilient as protected forests. A suite of 11 readily measured indicators emerged out of a first-principle approach to determining a holistic indication of soil health across a range of soils and systems in Hawaiʻi encompassing much of the diversity in the tropics and subtropics. Every land use may improve its soil health status within a reasonable range of expectations for a soil’s land use history, current land use, and mineralogy. Key drivers of inherent differences in the soil health indicators, including intensive land use history, current land use practices, and mineralogy, must be interwoven into the soil health index, which should set minimum and maximum benchmarks and weight indicators according to equitable standards.</p

Ecomimicry in Indigenous resource management: optimizing ecosystem services to achieve resource abundance, with examples from Hawaiʻi

Here, we expand on the term "ecomimicry" to be an umbrella concept for an approach to adaptive ecosystem-based management of social-ecological systems that simultaneously optimizes multiple ecosystem services for the benefit of people and place. In this context, we define ecomimicry as a strategy for developing and managing cultural landscapes, built upon a deep understanding of the structure and function of ecosystems, that harnesses ecosystem processes for the purpose of balancing and sustaining key ecosystem services, rather than maximizing one service (e.g., food production) to the detriment of others. Ecomimicry arises through novel, place-based innovations or is adopted from elsewhere and adapted to local conditions. Similarly, precontact Hawaiian social-ecological systems integrated a variety of ecomimicry schema to engender a complex system of adaptive resource management that enhanced biocultural diversity and supported resilient food systems, ultimately sustaining a thriving human population. In addition to presenting a synopsis of how ecomimicry was employed in the design and management of Hawaiian social-ecological systems, we identify and characterize specific ecomimicry applications. Within this context, we explore a revival of ecomimicry for biological conservation, biocultural restoration, resilience, and food security. We conclude with a discussion of how revitalizing such an approach in the restoration of social-ecological systems may address issues of conservation and sustainability in the Anthropocene