Lotfi Khiari

Phosphorus transformations in acid light-textured soils treated with dry swine manure

Organic matter can sorb P in acid soils through metal-organic matter-phosphate complexes. The pyrophosphate extractable Al and Fe and soil C contents were hypothetized to influence P partitioning in Ferro-Humic Podzols. Reaction of added P may be mitigated by adding lime or organic matter as dry swine manure (DSM) together with mineral P fertilizers. Three soils had 40 to 50 g kg-1 of soil organic matter (SOM) content, and 76 to 140 mmol (Al + Fe)pyro kg-1. A peaty soil phase had 200 g SOM kg-1, and 58 mmol (Al + Fe)pyro kg-1. Rates of monoammonium phosphate were 0, 27, 69, and 144 kg P ha-1 in a simulated fertilizer band. Rates of DSM and lime were 800 and 185–369 mg per 35 mL of soil, respectively. After 6 wk of incubation, soil P was fractionated sequentially into aluminium bound P (Al-P), iron bound P (Fe-P), and loosely bound P. Total P, desorbed P and organic P were determined in separate subsamples. A proportion of 79–92% of added P was recovered as Al-P and Fe-P in the three low SOM soils, compare...

Environmental Mehlich-III soil phosphorus saturation indices for Quebec acid to near neutral mineral soils varying in texture and genesis

The Mehlich-III method (M-III) (Mehlich 1984) is a multinutrient agri-environmental routine soil-testing procedure used in many jurisdictions in North America, but one that is affected by soil texture. The PW determined by the Sissingh (1971) method is an index of surface water contamination and desorbed P that is not influenced by soil texture and that can be used to define specific M-III critical environmental indices by soil texture group. Our objective was to define critical environmental indices by relating (P/Al)M-III to PW. We analyzed 275 soil samples from surface, and 175 from subsurface layers, varying in genesis, texture, and pH. The relationship between PW and (P/Al)M-III was influenced by soil properties, particularly soil texture and genesis. Fine-textured (> 300 g clay kg-1) and gleyed soils tended to release more PW at a given (P/Al)M-III compared with coarse-textured (≤ 300 g clay kg-1) and podzolized soils. Using a critical value of 9.7 mg PW L-1 derived from the literature, critical env...

Agri-environmental models using Mehlich-III soil phospho rus saturation index for corn in Quebec

Soil phosphorus (P), which is potentially a risk for environmental contamination, is currently interpreted using soil P saturation in North America. Our objective was to assess the ratio of P to aluminum (Al) in the Mehlich-III (M-III) soil test to build P requirement models for corn and soybean. We analyzed 129 corn and 19 soybean P fertilizer trials. For corn, the (P/Al)M-III ratio improved soil fertility classification compared with PM-III alone. The critical PM-III value as determined by the Cate-Nelson procedure was found to be 31.5 mg PM-III kg-1, close to published values. The critical (P/Al)M-III ratios of 0.025 for > 300 g clay kg-1 soils and 0.040 for ≤ 300 g clay kg-1 soils differed significantly between the two soil groups. For (P/Al)M-III ratios above 0.214, there was no positive response to added P for all soils regardless of texture. Using published critical environmental (P/Al)M-III ratios of 0.076 for > 300 g clay kg-1soils and 0.131 for ≤ 300 g clay kg-1 soils as benchmarks values, agri-...

Soil P-status and cultivar maturity effects on pea-Rhizobium symbiosis

In a green-house experiment, five cultivars of Pisum sativum L. grown on soils from 10 different locations in Tunisia, showed significant differences in nodulation, shoot dry matter (shDM) yield and shoot nitrogen content (shNC). The effect of soil on biological nitrogen fixation, as evidenced by the number and weight of nodules, was mainly attributable to the available phosphorus content. Cate-Nelson ANOVA analysis established a critical value of soil test phosphorus (STP) of 20 mg P kg−1 soil for nodule weight and number for the majority of cultivars. Within cultivars, nodulation varied with maturation period and was correlated with shoot NC. Thus, the overall interaction of soil-P content and cultivar-maturation period were correlated positively with nodulation and to symbiotic effectiveness of strains of Rhizobium leguminosarum bv. viceae indigenous to these soils. Based on an antibiotic susceptibility test and main variable factor analysis of the data obtained, 70 isolates of Rhizobia that nodulate pea, obtained from soils from agricultural sites throughout Tunisia, were identified as belonging to 18 distinct strains. These classes were identified on the basis of symbiotic efficiency parameters (shoot DM yield and shoot NC) as: ineffective (33 isolates), moderately effective (27 isolates), and efficient strains (10 isolates). This study shows that the Mateur site, an agricultural area for millennia in the northern region of Tunisia, harbors rhizobial strains that are highly efficient in fixing N2 with peas. These results also indicate the importance of strain-cultivar interrelationships and specificity.

Improving Physical Properties of Organo-Mineral Fertilizers: Substitution of Peat by Pig Slurry Composts

Some granulated organo-mineral fertilizers (OMF) are made with peat and their utilization is expected to increase mostly because of their advantages over mineral fertilizers. However, peat is a non-renewable resource and could be replaced by sustainable organic materials such as stabilized composted pig slurry. The objectives of this study were to determine the changes of OMF physical properties when 1) substituting peat by composted pig slurry mixtures, 2) changing source of composted mixtures, and 3) increasing the level of organic material in the OMF. Thirty-four mixtures of compost, monoamonium phosphate (MAP), diammonium phosphate (DAP), and peat were granulated in OMF at different proportions. The increase of the compost proportion and the decrease of organic material input (30% vs. 60% of organic materials) improved most physical properties of OMF granule such as bulk and granule densities, total and granular porosities, water content, abrasion fragility, crushing strength, critical relative humidity, and water sorption from moist porous media. In addition, most compost types resulted in similar physical properties of OMF granules. Finding the appropriate organic matter content requires more research and the optimum OMF mixture should be chosen as a function of its combined physical, chemical, and plant response properties.

A soil phosphorus saturation index decreasing scooped weight effect in mehlich‐3 procedure

Abstract The Mehlich‐3 method extracts a quantity of phosphorus (PM3) well correlated with crop yield in acid soils, and a quantity of aluminum (AlM3) well correlated with P sorption capacity of mineral soils. Phosphorus fertility levels in soils are generally determined on a volume basis, while soil sorption capacity for P and P saturation of the soil sorption capacity are assessed on a weight basis. However, scooped weights vary widely among tested soils. The purpose of this paper was to test the stability of a constructed ratio of PM3/AlM3 across a range of soil:solution ratios using 24 soils. Twenty‐four surface soils of different genetical and textural groups were extracted for PM3 and AlM3 without replication. Scooped weights varied between 3.21 and 4.17 g per 3‐mL scooped volume. Reproducibility of volumetric test (3 mL of soil per 30 mL of Mehlich‐3 solution) was within 3% for PM3, AlM3, and 100PM3/AlM3 using two contrasting soils with two replications. Extracted PM3 and AlM3 expressed on a weight...

Soil sample preparation techniques on routine analyses in Quebec affect lime and fertilizer recommendations

Abstract: Inadequate and (or) inconsistent soil sample preparation techniques (SPT) contribute to excessive variance, difficulties in soil test interpretation, and incorrect lime and fertilizer recommendations. The objective of this study was to evaluate the effect of SPT of five laboratories in Quebec (Canada) on chemical parameters measurement reliability. Samples of fine (G1), medium (G2), and coarse (G3) textured soils were collected from the surface layer. Three 500 g portions of each soil were sent to each laboratory for preparation. In addition, all samples were analyzed by the same laboratory for routine analyses. Nested ANOVA in a hierarchical model were performed with components of SPT interlaboratory reproducibility, SPT intralaboratory replicability, and intralaboratory soil analysis repeatability. Before samples were analyzed, we observed an important interlaboratory heterogeneity of particle size distributions for the same samples; due to sample preparation techniques, this can affect results of the analyses. Of all variables analyzed, the only significant, outside acceptable variations due to SPT were (1) pHwater in G1; (2) PM-III, AlM-III, and (P/Al)M-III in G1 and G2; (3) KM-III, CaM-III, MgM-III and organic matter in G3; and (4) MnM-III and CuM-III in G1, G2, and G3. The steps in SPT, mostly drying and crushing, require standardization to reduce the variance of the entire soil testing process.

Classification and assessment models of first year byproducts nitrogen plant-availability from literature data

Byproducts can provide an important amount of nutrients for crops and improve soils properties. According to their C/N, nitrogen (N) mineralization or immobilization may be observed after their application onto agricultural land. Therefore, an indicator is needed to assess byproducts N availability for crops. Thirty-seven studies from the scientific literature on N mineralization or immobilization after application to agricultural land under a wide range of climatic and experimental conditions were collected in order to elaborate models assessing non-composted byproducts N availability during the first growing season according to the C/N ratio. Four methods were used to evaluate N availability: incubation, apparent N recovery (ANR), relative N effectiveness (RNE) and fertilizer equivalence (FE). Since ANR was the model most related to C/N (R2=0.77), this model was used to define six categories of C/N. Results expressed in terms of FE were converted into RNE values. Although RNE is less precise than ANR, efficiencies of byproducts were expressed in terms of average RNE because it is the most appropriate for fertilization grids. Therefore, depending on C/N of non-composted byproducts, six categories were defined. i) high mineralization: +66% RNE and 5≤C/N, ii) moderate mineralization: +33% RNE and 5<C/N≤16, iii) low mineralization: +9% RNE and 16<C/N≤38, iv) low immobilization: -9% RNE and 38<C/N≤90, v) moderate immobilization: -27% RNE and 90<C/N≤140, and vi) high immobilization: -55% RNE and C/N>140.

Volume or Weight Soil Sampling for Extracting Mehlich III Elements with Routine Analyses

ABSTRACT The subsampling of soil for laboratory testing may be done by the volumetric or gravimetric methods. The specific method used may depend on regional or national regulations. Here, we present an analysis of the results, obtained by Mehlich III extraction, of 100 mineral soils and 24 organic soils in Quebec. Samples were selected by independent laboratories and were analyzed using the volumetric method (soil scoop), the volumetric–gravimetric method (using the soil scoop then weighing the scoop), and as a reference, the fully gravimetric method. The results showed that volumetric sampling was inadequate to accurately determine base cation content (KM-III, CaM-III, and MgM-III). Also, the volumetric–gravimetric method was inaccurate in determining the content of PM-III, AlM-III, and FeM-III. Moreover, the results reported using ratio-based indexes showed none of these imprecise behaviors and showed accurate results regardless of the sampling method.