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Addition of organic residues and their composts to enhance soil fertility results in organic N mineralization and transformations that may have profound effects on chemical processes. Our hypothesis is that carbonate precipitation and dissolution reactions are driven by proton consumption and release by organic N mineralization and nitrification. In the present study we evaluated the role of N-rich animal waste on carbonate dissolution/precipitation in a range of soil types. To discriminate the effects of organic C mineralization from nitrification we added a nitrification inhibitor, dicyandiamide (DCD), which slows NH 4 + oxidation without interfering with soil C respiration. Calcareous and non-calcareous soils were incubated with a pasteurized chicken manure (PCM) amendment with and without nitrification inhibitor DCD and control soil with and without DCD. Soil solution pH, extractable NH 4 + and NO 3 − , CO 2 emission and the concentrations of major cations in soil solution were determined. PCM application without DCD resulted in a pH increase in the first few days of the incubation followed by a pH decrease. DCD application effectively inhibited the nitrification process and the reduction in soil pH. The high correlation between nitrification and the reduction in pH indicated that the nitrification process was the main source of protons released, which led to carbonate dissolution and CO 2 emission from CaCO 3 . Application of DCD to PCM reduced CO 2 emission in PCM amended soils, especially in the earlier part of the incubation of calcareous soils. Furthermore, we found a linear 0.7:1 relation between the sum of cations (mostly Ca 2 + plus Mg 2 + ) released to solution due to proton production by organic N mineralization and nitrification that occurred in all soils with PCM applied, without DCD. Whereas, application of DCD to the PCM treatment inhibited nitrification and there was little or no proton production.

Root and microbial respiration is considered to be the main source of CO2 production in soil; however, calcite dissolution in calcareous soils may contribute to the emitted CO2. The major aim of this research was to quantify the contribution of CaCO3 dissolution to CO2 emission from a soil with and without the addition of an organic residue. Emissions of CO2 and its δ13C from incubated noncalcareous (Golan Heights [GH], −26.23‰) and calcareous (Bet She'an [BS], −11.47‰) soils with and without the addition of a pasteurized chicken manure (PCM, −23.2‰) were determined. During 56 d of incubation, 445 and 1804 mg kg−1 CO2–C emitted from BS and GH soils, and PCM application caused additional emission of 2430 and 1884 mg kg−1 CO2–C, respectively. The NO3−–N concentrations in the control BS and GH soils were 46 and 133 mg kg−1 and PCM application increased it to 508 and 577 mg kg−1, respectively. The emitted CO2–δ13C from BS and GH soils were −20.0 ± 0.2‰ and −27.2 ± 0.09‰ and application of PCM changed it to −20.6 ± 0.42‰ and −23.7 ± 0.16‰, respectively. Consequently, the contributions of the inorganic source to CO2–C emission from BS without and with PCM and from GH with PCM were 113.4, 417.5, and 176 mg kg−1 (26.5, 14.5, and 5% of the total), respectively. We suggest that oxidation of organic matter, mineralization of organic N, NH4 nitrification, oxidation of organic S, and production of organic acids caused chemical dissolution of calcite and CO2 emission. Ignoring this process will result in overestimation of the respired C.

The mechanism by which the anionic polymers interact with platelets of 2:1 clay minerals is not fully understood. The objective of the present study was to evaluate the effect of the electric field associated with the basal and edge surfaces of the clay minerals on the adsorption of anionic polymers. Two negatively charged polymers, PAM90 and ACC86, of the same molecular weig ht (2 × 105 g mol−1) but with different degrees of hydrolysis (90 and 20%, respectively), were used. The effect of pH (6, 10), NaCl concentration (0, 10 mmolC L−1) and clay particle size on PAM90 adsorption by pyrophyllite and the effect of NaCl concentration on the adsorption of these polymers by Na-montmorillonite in aqueous suspensions were studied. Adsorption of PAM90 on pyrophyllite was greater at pH 6 than at pH 10 and greater in 10 mmol L−1 NaCl than in distilled water. Adsorption of PAM90 on pyrophyllite increased with decreasing particle size. On pyrophyllite the high-charge-density PAM90 was adsorbed to a greater extent than the low-charge-density ACC86; by contrast, ACC86 adsorption was greater than that of PAM90 on Na-montmorillonite. These results were attributed to the repulsive forces which develop between the negatively charged extended-chain polymer and the extended negative electric field associated with the basal surfaces, around the Na-montmorillonite platelets. The results may suggest that the edge surfaces play a major role in PAM adsorption.

Polyacrylamide (PAM) is a long-chain synthetic polymer that acts as a strengthening agent, binding clay particles together. The interaction between anionic PAM and clay particles is not well understood yet. This interaction was evaluated by rheological measurements for Na-montmorillonite suspensions. Three anionic PAMs of three molecular weights (MWs) (3.5 ( 10 3 , 2 x10 5 , and 8 ×10 6 g mol -1 ) at similar hydrolysis levels (>85%) and three anionic PAMs at various degrees of hydorlysis (DH) (15, 33, and 92%) of similar MW were studied. In an electrolyte-free clay suspension at DH >85%, only the polymers with high MWs (2 X 105, and 8 x 10 6 ) could form a three-dimensional structure of clay platelets. The smallest polymer molecule size (3.5 x 10 3 ) was too short for bonding two adjacent platelets. At similar MW, the effect of the polymers increased with DH. At NaCl concentration of 10 mmol c L -1 , at which the attractive forces between clay platelets were weak, the polymers had a significant impact on flow behavior. The effectiveness of the polymers increased with increasing MW and DH. At NaCI concentration of 100 mmol c L -1 , the three polymers of DH > 85% stabilized floes that already existed in the clay suspension. The effectiveness of the polymers in bridging adjacent clay flocs increased as their DH decreased. The polymer conformation factor has a greater impact on clay structure stabilization in suspension than the electrostatic repulsion effect. The clay structure stability was increased with increasing polymer electrostatic negative charge for similar molecular weights.

Rheolo gical measurements were used to evaluate the particle-particle associations of Na-rich montmorillonite in suspensions, under various electrolyte concentrations. A 2% free electrolyte clay sus- pension showed pseudoplastic flow behavior and had a high apparent viscosity, attributed at low shear rates to the high volume fraction of the suspended clay platelets, the flexibility of the platelets, and the presence of edge-to-edge association. The breaking of edge-to-edge associations and the progressive orientation of the individual platelets in the direction of flow contribute to the reduction in viscosity with increasing shear rate. The compression of the diffuse double layer at a NaCI concentration of 10 mEq L -t contributes to the free movement of the individual platelets, even at low shear rates. The flow behavior changed from pseudoplastic to plastic at an NaCI concentration of 100 mEq L-L At this electrolyte concentration, face-to-face associations of specific junction points at certain areas of the planar surface are probably occurring. The apparent viscosity of the clay suspension for the two particle-size ranges (

Over the last decade there has been a dramatic shift in global agricultural practice. The increase in human population, especially in underdeveloped arid and semiarid regions of the world, poses unprecedented challenges to production of an adequate and economically feasible food supply to undernourished populations. Furthermore, the increased living standard in many industrial countries has created a strong demand for high-quality, out-of-season vegetables and fruits as well as for ornamentals such as cut and potted flowers and bedding plants. As a response to these imminent challenges and demands and because of a ban on methyl bromide fumigation of horticultural field soils, soilless greenhouse production systems are regaining increased worldwide attention. Though there is considerable recent empirical and theoretical research devoted to specific issues related to control and management of soilless culture production systems, a comprehensive approach that quantitatively considers all relevant physicochemical processes within the growth substrates is lacking. Moreover, it is common practice to treat soilless growth systems as static, ignoring dynamic changes of important physicochemical and hydraulic properties due to root and microbial growth that require adaptation of management practices throughout the growth period. To overcome these shortcomings, the objectives of this project were to apply thorough physicochemical characterization of commonly used greenhouse substrates in conjunction with state-of-the-art numerical modeling (HYDRUS-3D, PARSWMS) to not only optimize management practices (i.e., irrigation frequency and rates, fertigation, container size and geometry, etc.), but to also “engineer” optimal substrates by mixing organic (e.g., coconut coir) and inorganic (e.g., perlite, pumice, etc.) base substrates and modifying relevant parameters such as the particle (aggregate) size distribution. To evaluate the proposed approach under commercial production conditions, characterization and modeling efforts were accompanied by greenhouse experiments with tomatoes. The project not only yielded novel insights regarding favorable physicochemical properties of advanced greenhouse substrates, but also provided critically needed tools for control and management of containerized soilless production systems to provide a stress-free rhizosphere environment for optimal yields, while conserving valuable production resources. Numerical modeling results provided a more scientifically sound basis for the design of commercial greenhouse production trials and selection of adequate plant-specific substrates, thereby alleviating the risk of costly mistrials.

The use of organic residues as soil additives is increasing, but, depending on their composition and application methods, these organic amendments can stimulate the emissions of CO(2) and N(2)O. The objective of this study was to quantify the effects of management practices in irrigated sweet corn (Zea mays L.) on CO(2) and N(2)O emissions and to relate emissions to environmental factors. In a 3-yr study, corn residues (CR) and pasteurized chicken manure (PCM) were used as soil amendments compared with no residue (NR) under three management practices: shallow tillage (ST) and no tillage (NT) under consecutive corn crops and ST without crop. Tillage significantly increased (P < 0.05) CO(2) and N(2)O fluxes in residue-amended plots and in NR plots. Carbon dioxide and N(2)O fluxes were correlated with soil NH(4) concentrations and with days since tillage and days since seeding. Fluxes of CO(2) were correlated with soil water content, whereas N(2)O fluxes had higher correlation with air temperature. Annual CO(2) emissions were higher with PCM than with CR and NR (9.7, 2.9, and 2.3 Mg C ha(-1), respectively). Fluxes of N(2)O were 34.4, 0.94, and 0.77 kg N ha(-1) yr(-1) with PCM, CR, and NR, respectively. Annual amounts of CO(2)-C and N(2)O-N emissions from the PCM treatments were 64 and 3% of the applied C and N, respectively. Regardless of cultivation practices, elevated N(2)O emissions were recorded in the PCM treatment. These emissions could negate some of the beneficial effects of PCM on soil properties.