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Modern olive (Olea europaeaL.) mill extraction techniques generate a large amount of two‐phase olive mill waste (OMW) containing up to 90% organic matter. Recycling OMW as a soil amendment may represent a solution for its disposal, especially in Mediterranean areas, where many soils are characterized by very low organic matter levels. A 10‐yr field study was conducted to evaluate the long‐term sustainability of raw OMW disposal as a soil amendment on an olive grove in Elvas, Portugal. The soil was amended with OMW at rates of 0, 30, and 60 Mg ha−1, dry weight equivalent, for 8 yr, with cumulative and residual effects being assessed in the last year and 2 yr after the last application. Long‐term applications of OMW to soil led to cumulative and residual effects on soil physical [aggregate stability and bulk density (Db)], chemical [total organic carbon (TOC) and its humified fractions, total N, available P, and K], and biochemical [dehydrogenase (DH), urease (UR), β‐glucosidase (GLU), alkaline phosphatase (PHO), and arylsulfatase (ARS) activities] properties, and contributed to an increase in olive yields compared with the control (>17%, >1.47 Mg ha−1). However, electrical conductivity (EC) rose significantly with OMW application, especially in the residual year, ranging from 0.513 dS m−1for the unamended soil to 2.29 dS m−1at the 60 Mg ha−1application rate. Repeated addition of OMW to olive grove soils may be a useful strategy for recycling this organic amendment to improve soil fertility and increase yields. However, long‐term use of OMW increases the risk of soil salinity, especially if application rates are >30 Mg ha−1.

Low phosphorus (P) availability is a critical impediment to agricultural use of P-fixing soils. De-oiled two-phase olive mill waste (DTOMW) may be used as a soil amendment that can increase P availability and consequently improve crop production. The aim of this study was to investigate the effect of DTOMW amendments to soil on the fractionation, sorption, and buffering capacity of P in soils collected from a typical olive grove amended in the field with 27 and 54 Mg ha−1of DTOMW for 7 years. Cumulative and residual effects were evaluated in the last year of DTOMW application and 2 years subsequent to the last application. A modified Hedley fractionation scheme was used to evaluate the change in soil P forms, whereas the potential for sorption of P was evaluated by applying the surface Langmuir models to sorption isotherms. The P fractionation results indicated an increase in all P fractions (P< 0.05) in the studied samples. The order of the rates of increase in concentrations of P fractions was HCl-Pi > NaHCO3-Pi ≈ NaOH-Po > HCl-Po ≈ NaOH-Pi > H2O-Pi > NaHCO3-Po > residual P > H2O-Po in the cumulative year, whereas in the residual year, the order of increase was HCl-Pi > NaOH-Po > NaHCO3-Pi > H2O-Pi > NaOH-Pi > HCl-Po > residual P > NaHCO3-Po > H2O-Po. The DTOMW amendments significantly decreased the P sorption maxima (P< 0.05). Most of the total P sorption potential was attributed to low-energy sites, independent of the amendment applications received. The DTOMW soil application decreased indices of P-binding intensity at both high- and low-affinity sites, decreased the P equilibrium buffering capacity, and increased the equilibrium P concentration, indicating that P availability increased with increasing DTOMW rate and also with increasing humified organic matter fraction. This study has shown that in olive grove soils, successive DTOMW amendments may be an effective management practice for controlling their ability to fix inorganic P and increase P availability for the crop for at least 24 months after its application.

Two‐phase olive mill waste (TPOMW) is a by‐product of olive oil extraction, contains up to 90% organic matter, and may be used as soil amendment. To investigate the impact of TPOMW amendments to soil on the fractionation, adsorption, and buffering capacity of P, experiments were conducted on soils collected from a typical olive grove amended for 5 yr with 0, 30, and 60 Mg ha−1of TPOMW. A modified Hedley fractionation scheme evaluated the change in soil P forms while surface models were used to fit the data. The P fractionation results suggested and increase in HCl‐P fraction. Other P pools, such as residual‐P, NaHCO3–Pi, NaOH‐Pi, NaOH‐Po, soluble‐P, and NaHCO3–Po increased to lesser degrees. A two‐surface Langmuir model fit the adsorption data better than a uniform layer model and underestimation of the P adsorption was observed when the traditional Langmuir equation was used. The TPOMW amendments significantly decreased the P adsorption maxima (α = 0.05) and most of the P was adsorbed on low energy sites, independent of the amendment applications received. The TPOMW soil application decreased indices of P‐binding intensity at both high and low affinity sites, decreased the P equilibrium buffering capacity, and increased the equilibrium P concentration (EPC). Coupled with the low energy of P binding, results implied an increase in the readily soluble P, and thus runoff P losses could potentially increase in TPOMW amended soil.

Semiarid Mediterranean soils under intensive continuous cultivation have a net deficit of C, and addition of organic wastes is becoming a common practice as a disposal strategy and an interesting solution to redress this deficiency. A 2‐yr greenhouse study using wheat (Triticum aestivumL.) was conducted to evaluate the potential use of the final solid waste of the new technology of olive‐oil extraction (de‐oiled two‐phase olive mill waste, DTPOMW) as a soil conditioner and amendment agent. Two representative Mediterranean agricultural soils, a Typic Haploxeralf (TH) and a degraded Lithic Xerorthent (LX) were used. Treatments included five DTPOMW rates ranging from 0 to 40 Mg ha−1combined with mineral fertilizer. Significant direct and residual increases in organic C, total N, available K, cation exchange capacity, and aggregate stability were observed in both soils; however, available P decreased significantly. In the first year of the experiment, an application of 40 Mg DTPOMW ha−1had a depressive effect on grain yield and on the N and P content in the wheat grain for the LX soil, while in the TH soil there was a positive effect on yield at the same loading rate. There was an increased residual fertilization and amendment effect of DTPOMW for both soils during the second experimental year, and the grain yields increased by 23 and 202% when 40 Mg DTPOMW ha−1was applied to the TH and LX soils, respectively. For both soils, the best fits to grain yield vs. DTPOMW rates were with a quadratic regression (R2= 0.977, P< 0.001 for TH; R2= 0.983, P< 0.001 for LX). Raw DTPOMW may be a potentially valuable soil amendment agent and source of organic matter, N, and K because it maintains a positive, beneficial effect on wheat grain yield and soil properties for 24 mo following application.

Phosphorus (P) is the most limiting element in the Vertisols of southwestern Spain. There are few studies about P status, and crop responses to recommended P-fertilizer applications are erratic in these soils. The objectives of this work were (i) to investigate the P status and inorganic P fractions in these soils and (ii) to evaluate the relationships between soil inorganic P fractions, available P indices, and P uptake by plants. Total P, organic P, available P indices, and soil inorganic P fractions were studied in surface samples of 19 Vertisols of southwestern Spain. Total P uptake by Agrostis tennuiswas determined after 11 weeks of plant growth in a greenhouse, and was used to measure plant available soil P. Total P ranged from 168 to 482 mg P kg−1; soil organic P ranged from 42 to 125 mg P kg−1and averaged 28% of the total P. Soil inorganic P fractions were determined by a sequential-fractionation procedure (NH4Cl-P, NH4F-P, 0.1 MNaOH, CDB-P, 1 MNaOH-P, and H2SO4-P). Comparative rankings of the various inorganic P fraction quantities were H2SO4-P > NH4F-P > 0.1 MNaOH = 1 MNaOH-P > CDB-P > NH4Cl-P. Most of the inorganic P occurs in the least available form as Ca-P. The following soil test P extracted increasingly higher average amounts of P: Saunder (11.4 mg P kg−1), Truog (14.7 mg P kg−1), Olsen (17.8 mg P kg−1), Jackson (38.4 mg P kg−1) and Bray 2 (119.4 mg P kg−1). Jackson-P showed higher correlation with P uptake by the crop (r= 0.87) than did Olsen-P and Bray-P (r= 0.61 and 0.37, respectively), which are used to evaluate available P in the soils of the region studied. The results suggest that Jackson extractants removed easily soluble P as well as P from Fe and Al oxides. Moreover, organic P was an important fraction in supplying available P. A multiple regression model with Jackson-P, organic carbon, and cation-exchange capacity as independent variables explained 91% of the total variation in total plant P uptake. This implies that P availability and dynamics in these soils are influenced strongly by organic compounds and clay minerals.

Calculations of average molar Kerr constants <mK> of polypeptides of the twenty natural a-aminoacids in the random coil state are presented. The computation was carried out according to the Rotational Isomeric States model with the values of energies, dipole moments and optical anisotropies of the repeating units reported elsewhere. In the case of homopolypeptides, the ratios <mK>/x extrapolated to x?8 range approximately from -6000 to +5000 in units of 10-27V-2m5mol-1. Results obtained for ten actual proteins and three enzymes in the random coil state are also reported; their values of <mK>/x are very sensitive to the kind of aminoacid residues and to the sequence of those residues.

There are few studies about K status and K exchange equilibrium for Vertisols of southwestern Spain, and the K requirements for crop production in this region are not well defined. Moreover, there is no information on the relationship between the kinetics of K release and plant K uptake for these soils. The objectives of this work were (i) to investigate the K status in these soils, (ii) to investigate the kinetics of K release, and (iii) to compare the effectiveness of different extraction techniques for the prediction of K-supplying capacities. Kinetics of soil K release by successive extractions with 0.01 MCaCl2, extractable K using different soil extractants, and total K were studied in surface samples of 19 Vertisols in southwestern Spain. Total K uptake in three cuts of Agrostis tennuisgrown in the greenhouse was used to measure plant-available soil K. The following procedures extracted increasingly higher average amounts of soil K: 2 MNaCl (181 mg K kg−1), 0.1 MHNO3(285 mg K Kg−1), 1 MNH4OAc(371 mg K kg−1), and boiling 1 MHNO3(1328 mg K kg−1). Potassium release kinetics were described best with the Elovich equation, which showed the best fit of the four models tested. Elovich b values were most closely associated with K uptake by Agrostis tennuis(r= 0.942). Potassium extracted by 2 MNaCl and by 0.1 MHNO3showed higher correlation with K uptake by the crop (r= 0.905 and r= 0.899, respectively) than did 1 MNH4OAc (r= 0.724), which is used to extract K in the soils of the region studied. A multiple regression model with K extracted by 2 MNaCl and by 0.1 MHNO3as independent variables also explained 91% of the total variation in K uptake.

Low phosphorus availability is a critical impediment to agricultural use of Vertisols. Several studies have explored the P sorption characteristics of Vertisols, but few have investigated the relationship between soil physicochemical and the P sorption parameters calculated from uniform-surface and two-surface Langmuir equations. Phosphate sorption was investigated in surface-samples of 19 Vertisols in southwestern Spain. The phosphate sorption maxima (PAM) deduced from the uniform-surface Langmuir equationranged from 150 to 2566 mg P kg-1, with a mean value of 1115 mg P kg-1. The calculated sorption maxima (TPAM) for the two-surface Langmuir model ranged from 410 to 15406 mg P kg-1, and the mean value (4296 mg P kg-1) increased about 3 times compared with the basic Langmuir equation. The two-surface Langmuir model fit the sorption data better than the uniform layer model. Therefore, an underestimation of the P-sorption was observed when the traditional Langmuir equationwas used. Total surface area was highly correlated with sorption maxima: n= 0.708***for PAM and 0.900***for TPAM. For the two-surface equation, correlation analysis suggested that the “active” CaCO3(ACCE) was the most active sorbent of P on the high energy sites, whereas citrate-dithionite-bicarbonate extractable Fe (Fed) contributed to P sorption on the low energy sites. The prediction of the PAM and TPAM was improved by combining all or several of following soil properties: Fed, ACCE, clay, and total surface area in a multiple-regression analysis. The equations obtained could offer a rapid estimation of P-sorption in Vertisols of southwestern Spain. Moreover, the results obtained from a greenhouse experiment with Agrostis tennuisand two levels of P (0 and 218 mg P kg-1) showed that the amount of available soil P was a positive function of Fedbut a negative function for ACCE.