Shinjiro Sato

Assessing Methods for Developing Phosphorus Desorption Isotherms from Soils using Anion Exchange Membranes

Developing desorption isotherms for inorganic phosphorus (P) is a time-consuming and non-standardized procedure. Anion exchange membranes (AEMs) have been successfully used in studies of P desorption kinetics and total membrane-desorbable P, but rarely have they been used for developing P desorption isotherms. Our study had two objectives: (1) to evaluate the suitability of using multiple strips of AEMs (termed the Multiple AEM Method) to develop P desorption isotherms; and (2) to compare the Multiple AEM Method with a sequential-extraction approach using AEMs (termed the Sequential AEM Method) to determine if the manner in which AEMs were used would influence the slope of the desorption isotherm, i.e. the partition coefficient. Both methods yielded well-defined, but numerically different desorption isotherms for all levels of sorbed P. However, estimated Kd values among methods were equivalent in the low and medium levels of P sorbed. The Multiple AEM method was quicker than the Sequential AEM method, but both gave similar Kd values in an agriculturally significant range of soil solution concentrations. These methods should be tested on a range of soil type to determine their suitability in developing P desorption isotherms and to move toward method standardization for desorption isotherms.

Organic anions and phosphorus desorption and bioavailability in a humid Brazilian ultisol

Phosphorus (P) bioavailability is controlled by combined reactions of adsorption/precipitation and desorption/dissolution. Soil P has been fractionated; however, current P metrics do not necessarily measure discrete pools of bioavailable P based on mechanisms of soil inorganic P extraction by plants. Plants can desorb P by creating disequilibria between solid and solution phases (disequilibria desorption) and through the action of exuded organic anions on soil surfaces (ligand desorption). Both desorption mechanisms involve surface reactions of exchange and dissolution. These pools of P are potentially bioavailable pools because they react to plant mechanisms. However, these pools are not well documented. Our study had three objectives: (i) to measure ligand-desorbable P, (ii) to determine if we could separate ligand-exchangeable and ligand-dissolvable pools, and (iii) to investigate the fate of applied fertilizer P as it was incorporated into disequilibria-desorbable and ligand-desorbable pools. All studies used a tropical Brazilian Ultisol. Seven hours of interaction time and 500 &mgr;mol of anions g−1 soil were found optimum for the measurement of ligand-desorbable P. Our data suggested that ligand exchange and ligand dissolution could be operationally separable when anion concentrations were below 1 &mgr;mol g−1. In the short term, P fertilization preferentially put P in the disequilibria-desorbable pool over ligand-desorbable pool. Fractionation of soil bioavailable P must account for the mechanisms that plants and microorganisms have for extracting P from soils, which means they must go beyond the common P fractionation schemes commonly used today, which have their roots in soil pedology.

Nitrogen Recovery and Transformation from a Surface or Sub-Surface Application of Controlled-Release Fertilizer on a Sandy Soil

ABSTRACT Controlled-release fertilizers (CRF) are used to reduce leaching of nutrients, especially nitrate-nitrogen (NO3 −-N) to groundwater, caused mainly by application of soluble N fertilizers to sandy soils in Florida. A leaching column study was conducted to evaluate N release and transformation from a CRF (CitriBlen) over a 16-week period when it was applied on the soil surface or incorporated into the soil. When one pore volume of water was applied to column weekly or biweekly, the CRF released urea-N slowly over time with three peaks of release on 3–4, 8, and 12 week after application. Both ammonium-nitrogen (NH4 +-N) and NO3 −-N were leached in large amounts on week 2, likely from soluble forms of N. Cumulatively, the most leached N at the end of study was in the NH4 + form, followed by the NO3 − form. The sum of all N forms leached and volatilized accounted for 53–69% of total N applied. Total N recovery was 70% and 93% of total N applied for surface and sub-surface application of the fertilizer, respectively. It was indicated that the better recovery rate found with sub-surface application may have been due to minimized N loss by volatilization. Sub-surface application of fertilizer resulted in more than three times NH4 +-N remained in soil, compared with surface application. On average for both application treatments throughout 16-week period, 5.8 h was required for ammonification and 4.7 d for nitrification to occur after N release from the fertilizer. Characterization of CRFs for specific soil type, leaching volume and cycle, and application manner as well as knowledge of N requirement of the crop will allow for the Best Management Practices of these fertilizers, thus obtaining optimum yields and minimizing nutrient losses from CRFs.

Leachability and Vegetable Absorption of Heavy Metals from Sewage Sludge Biochar

Management of industrial wastes has been one of the most challenging problems in most urban municipalities due to increasing waste volume with limited disposal areas, and energy-consum‐ ing and high-cost treatment processes for disposal. In Japan, although the total volume of the industrial waste generated has been relatively constant since 1990 being approximately 400 million tons per year, remaining capacity of the final disposal for the industrial waste has decreased by approximately 20% since 1994, reaching to 172 million m3 in 2007 (Ministry of the Environ‐ ment Government of Japan, 2011). This disposal capacity is predicted to be filled in the average of 8.5 years for Japan, and 3.6 years for Tokyo Metropolitan areas. Due mainly to high cost of treatment for proper disposal, illegal dumping of the industrial waste has been a new problem despite of severe regulation and monitoring of affected areas. The number and total volume of unsolved cases of illegal dumping and improper disposal of the waste were 2,610 and 1.78 million tons, respectively, in 2010 (Ministry of the Environment Government of Japan, 2011).

Priming effect of bamboo (Phyllostanchys edulis Carrière) biochar application in a soil amended with legume

Abstract Biochar application to soils can mitigate carbon dioxide (CO2) by increasing soil carbon (C) sink, but also causes increased CO2 released from soils through priming effects of soil organic carbon (SOC). However, priming effects of biochar application on SOC are complex, showing inconsistent results, and further complicated when applied with other substrates such as organic amendment (OA). Incubation experiments were conducted using Typic Durudand with bamboo (Phyllostanchys edulis Carrière) biochar (400°C) and OA (crotalaria) applied individually, simultaneously or with biochar applied 5 weeks prior to OA application. After 56 d of incubation, cumulative CO2 released from soils with no amendments (control), biochar only (BC), OA only (OA), simultaneous (BC+OA), and differently timed (BCP+OA) applications reached 313, 326, 1270, 1535 and 1311 mg CO2 kg−1, respectively. The OA application distinctly increased CO2 released from the soils due to its decomposition. The OA decomposition rates were comparable with OA and BC+OA, while those with BCP+OA were lower than those with other treatments during early incubation. Net CO2 (CO2-(treatment) − CO2-control) from soils with BC, OA, BC+OA and BCP+OA yielded 13, 957, 1222 and 998 mg CO2 kg−1, respectively. Primed CO2-BC of 13 mg CO2 kg−1 was equivalent to 4.2% of priming effect relative to CO2-control. Primed CO2-BC+OA [net CO2-BC+OA − (net CO2-BC + net CO2-OA)] and primed CO2-BCP+OA were 252 and 28 mg CO2 kg−1, equivalent to 26% and 2.9% of priming effects relative to sum of net CO2-BC + net CO2-OA, respectively. The priming effect with BC was negligible likely because of limited amounts of biochar labile C to induce co-metabolism, while BC+OA showed a modest priming effect most likely as a result of co-metabolism induced by additional mineralization of presumably SOC and/or biochar, because the OA decomposition rates were not affected by biochar application. The priming effect with BCP+OA was comparable to that with BC likely due to changes in soil properties caused by biochar application prior to OA, likely from slowed decomposition rates of OA.

Nutrient Mobility and Availability with Selected Irrigation and Drainage Systems for Vegetable Crops on Sandy Soils

A wide variety of vegetable crops is produced on varying types of soils including sandy soils where the production can be maximized as long as proper fertilization, irrigation and drainage systems are implemented. However, most sandy soils have low waterand nutrient-holding capacities, hence appropriate irrigation scheduling is critical for proper plant health as well as for minimizing water requirement. Healthy crops are better able to withstand pest and disease pressures, as well as produce a high quality commercial product. Irrigation management should be geared towards maintaining optimum moisture and nutrient concentrations within the plant root zone. If this goal is achieved, crops will take up their maximum amounts of water and nutrients with minimum wastage. Equally important, excessive irrigation will reduce water use efficiency, as well as require more water and contribute to potentially negative environmental impacts. It is crucial to recognize how nutrients move and transform in soils after the application for improved application efficiencies and reduced environmental losses. However, different irrigation and drainage systems practiced on sandy soils for vegetable production can complicate the dynamics of mobility and availability of nutrients and water. Yet, the number of researches on this matter has not been as many as needed. Therefore, this review attempts to summarize characteristics of sandy soils for vegetable production (Section 2), clarify pros and cons of different irrigation and drainage systems practiced on sandy soils (Section 3), and elucidate the nutrient mobility and availability for vegetable production under different irrigation systems specifically on sandy soils (Section 4), in which the soil environment can greatly differ from other soil types in terms of nutrient dynamics in soil.