ALBERT

Description: The objective of this study was to compare several methods of estimating the availability of soil nitrogen to plants. Total soil N, organic matter content, mineralized N during a 2 wk incubation at 35 °C, organic N in 6 N HC1, 0.01 M NaHCO3 and 1 N KCl extracts, and finally mineral N extracted by 2 N KCl were evaluated and contrasted with N uptake by sugar beets cultivated on 19 soils in a greenhouse experiment. The relative yield or plant N uptake gave the highest correlation coefficients when both mineral and organic N fractions in soil extract were considered. The incubation methods gave the best correlation coefficient with relative yield (R2 = 0.85**). N contents in NaHCO3 extract were more correlated with relative yield or N uptake than total N, organic matter contents or N extracted by 6 N HCl or 1 N KCl. The UV absorbance values obtained at 205 nm with 0.01 M NaHCO3 extract were also well correlated with relative yield (R2 = 0.78**) and plant N uptake (R2 = 0.66**). At this wavelength, as well as at 220 nm, the absorbance was affected by mineral and organic N contents in the extract. However, at 260 nm, the UV absorbance was only related to organic N in the extract; consequently these absorbance values were less correlated with relative yield (R2 = 0.49**) or N uptake (R2 = 0.27*). Furthermore, the absorbance measured at 205 nm was too sensitive to NO3-N and organic N concentration and this relationship was not linear in the high-N concentration range. The UV absorbance at 220 nm in the 0.01M NaHCO3 extract seemed to be a promising method to evaluate the availability of soil N. Key words: Soil nitrogen, incubation, ultraviolet absorbance, hydrolyzable nitrogen

Description: The objective of this study was to evaluate different available P extracting methods in relation with soil properties, oat yield and plant P uptake. Six chemical extractants (Bray-1, Bray-2, new Mehlich, North Carolina DA-4, DA-10, and Olsen) and two anion exchange resins (F− and HCO3−) were compared on 42 acid soils. The DA-4, DA-10, new Mehlich, and HCO3− resin methods showed the best correlation with oat yield and plant P uptake. The Bray-1, Bray-2 methods were significantly less correlated than the other methods. The HCO3− resin was better than F− resin to predict plant P uptake and yield. Available P levels as determined by these eight methods were classified poor, medium and rich by the Cate and Nelson procedure. Oxalate extractable Al, pH (NaF), pH (H2O), exchangeable (Ca + Mg), forms of P, maximum P fixation capacity and soil texture have great influence on the plant P uptake. Soil organic matter content and oxalate-extractable Fe had significantly less important an effect. The Bray-1 and Bray-2 methods were the most affected by soil properties especially oxalate-extractable Al. The P-HCl/P-DAF ratio proposed by Mehlich to identify forms of soil P indicated that seven soils contain predominantly Ca-P and 21 soils with predominantly Al-P and Fe-P. This ratio was related with oxalate extractable Al (r = − 0.32*), pH NaF (r = − 0.59**), pH H2O (r = 0.52**) and exchangeable Ca + Mg (r = 0.55**). The maximum P fixation capacity (M) ranged from 150 to 4200 μg P/g soil and was closely related with oxalate-extractable Al (r = 0.81**), pH NaF (r = 0.74**), pH H2O (r = − 0.36*) and Mehlich ratio (r = − 0.33*). The maximum P buffering capacity (Mb) of soils was also measured and showed the best correlation with oxalate-extractable Al (r = 0.84**) and pH NaF (r = 0.53**). Key words: Soil testing, available P, anion exchange resins, P fixation, oxalate-Al, forms of P

Description: Seven chemical methods (Bray-II, Bray-I, North Carolina DA-4, DA10, Mehlich II, Mehlich III and Olsen) and two anion exchange resins (F− and [Formula: see text] forms) were evaluated on 43 soils with pH varying from 6.4 to 7.88. A greenhouse experiment was carried out with ryegrass receiving two treatments (without P fertilization and 150 mg kg−1 soil) on these soils. The Olsen's method and the two anion resins used as reference ones were effectively the better correlated with P uptakes (r = 0.83**–0.87**) and relative yield (R2 = 69.3–70.2%). The Mehlich II, Mehlich III and to a lesser extent Bray-I methods showed good correlations with these reference methods (r = 0.77**–0.83**) and with plant P uptakes (r = 0.73**–0.79**) or relative yields (R2 = 48.9–55.1%). The Bray-II, DA-4 and DA-10 methods may dissolve some calcium phosphates such as apatites or tricalcium phosphate in some soils and thus overestimated their available P content. The P amounts extracted by these methods were less correlated with P uptakes (r = 0.57*–0.67**) or relative yields (R2 = 14.4–31.4%). On the other hand, the DA-4 extractability was diminished in soils containing more than 3% of carbonates. Although the Ca-P was the predominant form in these soils, the P fixation capacity (M) and maximum P buffer (Mb) capacity were mostly related with Al and Fe-oxalate contents. However, the low Mb values obtained from these soils indicated that the P concentration in soil solution is more favored with respect to adsorbed P. Organic matter and clay contents, pH (H2O), exchangeable Ca and carbonate contents had some effects on the extraction capability of some methods without affecting plant P uptakes. Key words: Available P, soil testing, anion exchange resins, soil properties, P fixation

Description: The efficiency of 15N-labelled fertilizer on early harvested potaotes (Solanum tuberosum L., 'Norland') was studied in field experiments on two soil series (Saint-Damase loamy sand and Soulanges sandy loam) during a 2-yr period. The 15NH415NO3 fertilizer was band applied at 0 and 140 kg N ha−1 in 1985 and 0, 70, 140 kg ha−1 in 1986 and four harvests were made during the growing season. The foliage was in full canopy development at 65 or 75 d and its dry matter yield increased significantly with the application of fertilizer-N. At this time about 70% of the total N uptake was in the foliage. From this peak, foliage N decreased gradually with time to about 28% at 95 or 100 d as N was transferred to the tubers. The N concentration in tubers was nearly constant during the growing season. As tuber dry matter increased at each successive harvest, N uptake increased proportionally. Between the first two harvest dates, from 65 to 75 d, the average rates of N accumulation in tubers were 2.1 and 4.5 kg N ha−1 d−1 for the control and N fertilized plot, respectively. The root dry matter and N concentration increased with fertilizer-N and were generally lowest on the final harvest day. Marketable tuber yield responded to N fertilization on the severely N-deficient fields in 1985. But in 1986, the 140 kg N ha−1 treatment delayed the growth of marketable tubers. The percentage of N derived from fertilizer (Ndff) was also very high in 1985 fields and was at a maximum at 65 d (64–69%) with the 140 kg N ha−1 treatment. These values were lower for the same treatments in 1986 fields (39%) because of the larger amounts of available N in soils. The maximum coefficient of utilization (ICU) of labelled fertilizer N was 72–76% in 1985 and 63–68% in 1986. At the final harvest, about 36–50% of the applied fertilizer-N was found in the tubers. Key words: Nitrogen fertilization, 15N-labelled fertilizer, N use efficiency, harvest periods, potato

Description: The objectives of this study were to compare the EUF procedures (50, 200 and 400 V) and some chemical methods (1 N NH4OAc, 0.01 M CaCl2, 1 N HNO3) in order to estimate the K fertility levels of 60 Quebec soils. The EUF-50 V-K quantities corresponded to CaCl2-K while EUF-(50 + 200 + 400 V) to acetate-K. The relations between EUF-(50 V)-K, EUF-(200 V)-K to Acetate-K were improved when introducing clay contents, CEC values and K saturation levels. On the other hand, soil pH, carbonate and exchangeable (Ca+Mg) contents had significant effects on the relations between EUF-400 V-K and Acetate-K. A greenhouse experiment, using ryegrass as the test plant, was carried out on these soils with two treatments (complete fertilization with and without K). EUF-400 V-K, Acetate-K and EUF-(50 + 200 + 400 V)-K were the best criteria to estimate relative yields and K uptake by the plant. EUF-(50 + 200 V) underestimates K fertility level for soils rich in clay, having high pH (H2O) or exchangeable (Ca+Mg) contents. Higher correlation coefficients for K uptake by the plant were obtained in multiple regression where EUF-(50 + 200 V)-K and EUF-400 V-K were taken into account. The relation between plant K uptake and K values determined by all methods were improved by considering the K saturation levels on cation exchange sites. Acetate-K contents explained up to 88% of the variation in K uptake when K saturation level was introduced. Finally, this method can overestimate the K fertility levels for soils rich in clay or organic matter. Key words: Electro-ultrafiltration, available K, soil properties, exchangeable K

Description: The objective of this study was to compare different available-P extracting methods on 83 Québec soils. The alkaline Olsen’s method and five acid chemical extractants (Bray-1, Bray-2, new Mehlich, North Carolina double acid DA-4 and DA-10) were compared with each other and with two anion-exchange resin methods. The ratio of P-HCl/P-DAF of Mehlich was used to identify the group of soils with predominant P-Ca forms [Formula: see text]. Within this soil group, the Bray-2, DA-4 and DA-10 methods extracted more P and they were less correlated with all the other methods (r = 0.01 to 0.48*). The Bray-1 and Mehlich methods showed good relationships with Olsen, F−- and HCO3−-form resin methods (r = 0.80** to 0.89**) for this soil group, with the exception that Bray-1 solution was more affected by the presence of free carbonates. In the soil group containing more than 0.6% oxalate-Al, the Bray-1, Bray-2 and DA-10 methods extracted more P than the Mehlich, DA-4 or Olsen methods. The F−-form exchange resin extracted more P than that in the HCO3− form. The depressing effect of free iron oxides on the DA-4 method was also observed with the soil group containing more than 0.6% oxalate-Fe. The contents of DA-4-P were less correlated with those of other methods (r = 0.74** to 0.88**) in this soil group. On the other hand, the Olsen, F− and HCO3− resins extracted more of the P-Fe forms from these soils. The DA-4 method was further influenced by the soil organic matter (OM) contents. The relationships between P-Olsen, P-HCO3−-resin with the other chemical methods were also improved by taking into account the contribution of OM contents. Soil texture influenced mostly Bray-2, Bray-1, DA-4 and DA-10 extractable P. The Mehlich, Olsen and F−-resin extractable P was less affected by clay contents while the HCO3−-resin was the most consistant over a wide range of soil textures. Key words: Available-P, anion-exchange resins, new Mehlich extractant, P-forms, soil testing

Description: The objective of this study was to compare extractable potassium levels removed from soils by electro-ultrafiltration (EUF) and by conventional chemical soil tests. Accordingly, concentrations of potassium removed from soils by three EUF and six chemical extraction procedures were compared, on a group of 50 soils which contained less than 20% clay and on a second group of 52 soils which contained from 20 to 50% clay, by means of regression and correlation techniques. The following three EUF extraction procedures were tested: (i) 50 V at 5-min; (ii) 50 V at 5-min plus 200 V at 25-min; and (iii) 300 V at 15-min. Results indicated that the concentrations of soil K found in the combined anolyte and catholyte of the EUF or removed by the chemical procedures were very closely related (r-values generally greater than 0.90). However, EUF was less efficient in removing K from soils containing higher proportions of clay than NH4OAc, the new Mehlich solution, or the double acid mixture used at 1:30 wt/vol soil-solution ratio. As soil K fractions extracted by different EUF procedures were closely related among themselves as well as between the chemical methods tested, EUF would not provide soil fertility information that could not be obtained by less laborious and expensive chemical procedures. Key words: Soil testing, NH4OAc, double acid, new Mehlich extractant, electro-ultrafiltration

Description: Resin extraction procedures are widely used to simulate nutrient uptake by plant roots. The objective of this study was to compare an anion exchange resin in three forms: F, Cl and HCO3, and a mixed anionic-cationic exchange resin in H-OH form to a 32P isotopic exchange method in their ability to extract soil P, and to predict plant-available P for oat (Avena sativa L.) grown in the glasshouse. Thirty-four soils varying widely in chemical and physical properties, and in P contents, were extracted for 24 h at a soil-to-solution ratio of 1:80 with 1 g resin. Increasingly higher P quantities were obtained by isotopic exchange after 1 min (E1 7.61 mg kg−1), Cl-resin (27.3 mg kg−1), HCO3-resin (40.5 mg kg−1), F-resin (75.1 mg kg−1) and H-OH resin (130 mg kg−1). The Cl and HCO3 resins extracted a constant ratio of E1-P in strongly acidic and weakly acidic to neutral soils; this was not the case for the other resins. The pH values of the resin-soil-solution system were related to the natural logarithm of the amount of rapidly exchangeable Ca. The Cl and HCO3 resins best predicted P uptake and relative yield of oat growing on 34 soils. These two methods were superior to chemical methods in evaluating soil P status and fertilizer response of oats. The relationships between the amount of soil P desorbed by the HCO3 and F resins and by plant uptake were improved when the P buffering capacity (MBC) was included in the multiple regression equation. The P intensity factor was most important for the H-OH and Cl resins. In general, desorption of soil P with exchange resins improves, compared to chemical extradants, the evaluation of the P-supplying power of soils. Key words: 32P, anion exchange resin, available P, extraction method