Status and distribution of soil sulphur fractions,total nitrogen and organic carbon in camp and non-camp soils of grazed pastures supplied with long-term superphosphate

Summary Topsoils (0–75 mm) from four different soil types were collected from stock camp and non-camp (main grazing area) areas of grazed pastures in New Zealand, which had been fertilised annually with superphosphate for more than 15 years, in order to assess the effects of grazing animals on the status and distribution of soil S fractions and organic matter. These soils were analysed for organic C, total N, total S, C-bonded S, hydriodic acid-reducible S, 0.01 M CaCl₂, and 0.04 M Ca(H₂PO₄)₂-extractable S fractions, and soil pH. Soil inorganic and organic S fractions extracted by NaHCO₃ and NaOH extractants were also determined. The results obtained showed that camp soils contain higher soil pH, organic C, total N, total S, organic (C-bonded S and hydriodic acid-reducible S) and inorganic S fractions, NaHCO₃-and NaOH-extractable soil S fractions but a lower anion retention capacity than non-camp soils, attributed to a higher return of plant litter and animal excreta to camp soils. In both soils, total S, organic S, C-bonded S, and hydriodic acid-reducible S were significantly correlated with organic C (r0.90***, ***P0.001) and total N (r0.95***), suggesting that C, N, and S are integral components of soil organic matter. However, C: N : S ratios tended to be lower in camp (60: 5.6: 1–103: 7.2: 1) than in non-camp soils (60:6.1:1–117:8.3:1). Most (>95%) of the total soil S in camp and non-camp soils is present as organic S, while the remainder is readily soluble and adsorbed S (i.e. Ca(H₂PO₄)₂-extractable S). C-bonded S and hydriodic acid-reducible S constituted 55%–74% and 26%–45% of total S, respectively, reflecting a regular return of plant litter and animal excreta to the grazed pastures. NaHCO₃, and especially NaOH, extracted significantly higher amounts of total soil S (13%–22% and 49%–75%, respectively) than Ca(H₂PO₄)₂ or CaCl₂ (<5%). In addition, NaHCO₃ and NaOH-extractable soil S fractions were significantly rorrelated with soil organic S (r0.94***), C-bonded S (r0.90***) and hydriodic acid-reducible soil S (r0.93***). Differences between soils in either camp or non-camp areas were related to their sulphate retention capacities, as soils with high sulphate retention capacities (>45%) contain higher levels of C-bonded and hydriodic acid-reducible S fractions than those of low sulphate retention soils (<10%). Long-term annual superphosphate applications significantly increased the accumulation of soil organic and inorganic S fractions, and organic C and total N in the topsoil, although this accumulation did not occur when the superphosphate application rates were increased from 188 to 376 kg ha^-1 year^-1.     

Sulphur in soil and light fraction organic matter as influenced by long-term application of superphosphate

Numerous studies have examined the role of light fraction (LF) organic matter in soil C and N cycling, but there is no published information on the amounts and nature of S in LF. The objective of this work was to characterize the S composition of LF in soils receiving different inputs of fertilizer S. Soils (0-7.5 cm) were taken from a long-term experiment (1952-1999) set up to examine the effects of single superphosphate (SP) (applied at 0, 188, or 376 kg ha⁻¹ yr⁻¹, which equates to 0, 21, and 42 kg SO₄-S ha⁻¹ yr⁻¹) on the productivity of an irrigated, grass-clover pasture grazed by sheep. The S content of LF (separated by flotation on NaI solution with specific gravity 1.7) increased by ∼20-30% in response to SP. The LF was enriched in organic S compared with whole soil (S concentration in LF was ∼1000-1400 mg kg⁻¹ vs ∼400-500 mg kg⁻¹ in whole soil), but LF-S represented only 1.3-4.7% of soil S. Most (∼88%) of the S in LF was C-bonded, reflecting the dominance of this form of S in organic matter returned to the soil in dung and plant residues. Hydriodic acid (HI) reducible-S accounted for only ∼12% of LF-S, compared with 28-35% of whole soil organic S. Superphosphate tended to increase total soil N, due to improved clover growth. There was a strong positive relationship between total N and C-bonded S in whole soil and LF, whereas soil HI-S and N were not associated. Increases in C-bonded S where SP was applied appeared to be driven mainly by increases in soil N, which in turn were due to improved clover growth in response to phosphate supplied by SP. Increases in HI-S due to SP application were probably a direct response to inputs of S. As LF is a small pool of S, with a relatively wide C:S ratio (∼200:1), we concluded that it is unlikely to contribute a significant amount of plant-available S.     

Evaluation of extractants for predicting availability of sulphur to mustard in inceptisols

Abstract

Mustard (Brassica juncea) is an important oilseed crop of northern India, which is widely grown in Delhi and adjoining States. This crop has a relatively high requirement of sulphur (S), and is sensitive to S‐deficiency. For predicting response of mustard to S application, several extractants have been tried with variable results. Since selection of a promising extractant for a particular soil needs careful consideration, the present investigation was planned to select the most promising extractant to predict the availability of S to mustard grown on Inceptisols of Delhi. For this purpose, a greenhouse experiment was conducted with twenty soils (two from each often important soil series from the cultivated alluvial soil belt of Delhi. Nine extractants, commonly used for estimating the availability of S, were evaluated and S in soil extract and in plant digest was estimated using the turbiditimetric method. The results indicate that the phosphate salt methods extracted comparatively more S than other extractants. The amount of S extracted by these extractants was found in the following order: KH₂PO₄‐500 ppm P>Ca(H₂PO₄)₂‐500 ppm P>0.001 M HCl>NaOAc+HOAc>heat soluble S>0.15% CaCl₂>l% NaCl> water soluble S>NH₄OAc+HOAc. Simple correlation coefficients of the amounts of S extracted by different extractants and the forms of S with the plant parameters were worked out. To determine the combined effect of soil characteristics on S extraction by different extractants, stepwise multiple regression analysis was carried out. Based on this study, the suitability of the extractants for mustard crops in Inceptisols of Delhi may be arranged as follows: 0.15% CaCl₂>water soluble S>0.001 M HCl>Ca(H₂PO₄)₂‐500 ppm>1%NaCl>NH₄OAc+HOAc>NaOAc+HOAc>KH₂PO₄‐500 ppm P>heat soluble S.     

Comparison of Seven SO4-S Extraction Methods for Analysis by Turbidimetry or ICP Spectrometry

Soil sulfur (S) analyses for fertilizer recommendations in the northern Great Plains often do not reflect crop S requirements. Seven SO₄-S extraction methods with S determination by either turbidometry or inductively coupled plasma emission spectroscopy including Ca(H₂PO₄)₂ and KH₂PO₄ (both containing 500 ug/l P), 0.25 M KCl (40 ºC) and 0.25 M KCl (room temperature), H₂O, DTPA, and Mehlich 3 extractants. Three horizon depths of three soils from a previous field study were used for these comparisons. Average standard deviations for turbidometric determinations were 4.3 times greater than ICP determinations. With turbidometry, S values were H₂O > KH₂PO₄ > Ca(H₂PO₄)₂ > KCl (40 ºC) = KCl, while with ICP, the values were Mehlich 3 > KCl (40 ºC) = KCl > DTPA (diethylenetriaminepentaacetic acid) > KH₂PO₄ > H₂O > Ca(H₂PO₄)₂. Extraction with KCl at room temperature with ICP determination appears to show promise, but further method evaluation is necessary before it can be recommended as a SO₄-S test method.     

Chemical fractionation,water solubility and temporal distribution of sheep faecal sulphur fractions in grazed pastures receiving long‐term sulphate fertilization

Abstract

Although over 40% of excretal S is returned to intensively sheep ‐grazed pastures as faecal S, limited information is available on faecal S fractions, their water solubility and temporal distribution. This study reports results obtained from sheep faeces returned to grazed pastures which have received long‐term annual sulphate applications for 15–20 years. Five freshly‐voided sheep faecal samples (<100 g moist faeces per sample) per sampling were randomly collected at approximately one month intervals over a one‐year growing season. Faeces were fractionated into total S, inorganic SO₄ ^2‐, ester SO₄ ^2‐, Hi‐reducible S and C‐bonded S. Results obtained showed that faecal total S, ester SO₄ ^2‐ Hi‐reducible S and C‐bonded S fractions varied significantly throughout the year. Carbon‐bonded S was the dominant (>80%) faecal S fraction, regardless of faecal total S content or the time of year faecal samples were deposited. Faecal ester SO₄ ^2‐ and inorganic _SO₄ ^2‐fractions accounted for 3.3–7.1% and 0.1–14% of faecal total S respectively. Thus approximately 3.4–21.1% of faecal total S was estimated to be potentially leached or readily available to pasture plants. The Hi‐reducible faecal S fraction was significantly‐correlated (r = 0.59***; *** = P ≤ 0.001) with HCl‐extractable faecal inorganic S, which was considered to represent faecal total SO₄ ^2‐ (ester SO₄ ^2‐ and inorganic SO₄ ^2‐ fractions).

The solubility of different faecal S fractions was determined by sequential extraction of ground (< 1 mm) faeces three times (30 minutes per extraction) with water or 0.01 M Ca(H₂PO₄)₂ solution (1: 5 ratio of faecal DM: extractant). Both amounts of water‐extractable and Ca(H₂PO₄)‐extractable faecal S fractions were found to vary significantly throughout the year. Ca(H₂PO₄)₂ tended to extract more inorganic faecal S than water, attributed to the presence of phosphate and the low pH (pH=4) of Ca(H₂PO₄)₂ extractant. A significant proportion (15–25%) of faecal S was extracted by water and most (70%) of this water‐extractable faecal S was in the organic S fraction. Water‐extractable inorganic faecal S probably originated from the faecal total SO₄ ^2‐ fraction as shown by their significant correlation (r = 0.45** ‐0.63***; ** = P≤ 0.01; *** = P≤ 0.001). Some of the faecal S in water extracts may also originate from the faecal C‐bonded S fraction, as a significant correlation was obtained between C‐bonded faecal S and either water‐extractable faecal organic S (r = 0.53–0.57***; *** = P ≤ 0.001) or water‐extractable faecal inorganic S (r = 0.40–0.41*; * = P ≤ 0.05).

Significant amounts of faecal inorganic SO₄ ^2‐ and ester SO₄ ^2‐ fractions were removed by Ca(H₂PO₄)₂ extractant. The Ca(H₂PO₄)₂‐extractable faecal inorganic S was significantly correlated (r = 0.73***^; *** = P ≤ 0.001) with water‐extractable faecal inorganic S.     

Sulphur mineralization and release of soluble organic sulphur from camp and non-camp soils of grazed pastures receiving long-term superphosphate applications

Summary Topsoils (0–75 mm) from four soil types with different sulphate retention capacities were collected from stock camp and non-camp (main grazing area) sites of grazed pastures in New Zealand which had been annually fertilized with superphosphate for more than 15 years. These soils were analysed for different S fractions and incubated at 30°C for 10 weeks using an open incubation technique in order to assess the extent of S mineralization and the release of soluble soil organic S from camp and non-camp soils during incubation. The soils were preleached with 0.01 M KCl, followed by 0.04 M Ca(H₂PO₄)₂ before being incubated. Pre-incubation leachates and weekly 0.01 M KCl leachates were analysed for mineralized S (i.e., hydriodic acid-reducible S) and total S. Soluble organic S was estimated as the difference between these two S fractions. Results obtained show higher cumulative amounts of all three S fractions in leachates over a 10-week incubation period in camp than in non-camp soils, suggesting that higher mineralization occurred in camp soils. Cumulative amounts of mineralized S from camp and non-camp soils showed a linear relationship with duration of incubation (R ²0.985^***), while the cumulative release of soluble organic S followed a quadratic relationship (R ²0.975^***). A significant proportion (14.6%–40.8%) of total S release in KCl leachates was soluble organic S, indcating that organic S should be taken into account when assessing S mineralization. Mineralized S and soluble organic S were best correlated with 0.01 M CaCl₂-extractable soil inorganic S (R ²=0.767^***) and 0.04 M Ca(H₂PO₄)₂-extractable soil inorganic S(R ²=0.823^***), respectively. Soil sulphate retention capacity was found to influence amounts of mineralized S and soluble organic S, and thus periodic leaching with KCl to remove mineralized S from soils may not adequately reflect the extent of soil S mineralization in high sulphate-retentive soils. In low (<10%) sulphateretentive soils, increasing the superphosphate applications from 188 to 376 kg ha^–1 year^–1 increased S mineralization but not amounts of C-bonded and hydriodic acid-reducible soil S fractions.     

灌溉模式和有机肥配施对水稻产量、光合特性和氮肥利用率的影响

针对湘北地区农业水资源日益紧缺和水稻生产上滥施化学氮肥的现状,为了节约淡水资源、降低化肥用量、实现水肥协同和资源高效利用,设置2种灌溉方式(W₁：全生育期淹水灌溉;W₂：全生育期湿润灌溉)和4个施氮水平(N₀：不施氮肥;N₁：施N量150 kg/hm²,肥料为尿素氮100%;N₂：施N量150 kg/hm²,肥料为尿素氮80%+有机氮(菜枯)20%;N₃：施N量150 kg/hm²,肥料为尿素氮60%+有机氮(菜枯)40%),分析水稻产量、光合特性、氮素代谢和氮肥利用率对灌溉模式和有机肥配施的响应规律。结果表明：与W₁相比,W₂显著增加水稻产量、氮肥利用率、净光合速率、蒸腾速率、气孔导度等;在不同施氮处理下,增加有机肥比例能显著提高产量,N₃、N₂、N₁分别比N₀     

Effect of plant material parameters on nitrogen mineralization in a mollisol

Abstract

The introduction of plant materials into a soil can impact the nitrogen (N) status and the fertilizer requirement for agronomic crop production. Consequently, an accurate estimate of N mineralization from soil organic matter and incorporated plant material is necessary to adequately make a N fertilizer recommendation. The purpose of this study was to evaluate the effect of plant parameters including type, size, incorporation rate, and time after incorporation on N mineralization and to derive localized values for parameters in a widely used potential N mineralization model. Soil from the Ap horizon of a Latahco silt loam was amended with alfalfa (Medicago saliva L.), spring pea (Pisum sativum L.), and winter wheat (Triticum aestivum L.) plant materials sized to either <1,1 to 2, or > 2 mm at rates of 0, 2, 4, and 6%. The soils were incubated at 35°C for 20 weeks. The inorganic N in soils was removed by leaching with 100 mL 0.001M CaCl₂ in 5‐ to 10‐mL intervals followed by 25 mL of a nutrient solution devoid of N (0.002M CaSO₄; 0.002M MgSC>₄; 0.005M Ca(H₂PO₄)2; and 0.0025M K₂SO₄) at 0, 2, 4, 6, 8, 12, 16, and 20 weeks. The main effects of plant material type (PM), size (S), incorporation rate (R), and incubation time (T) and many 2‐, 3‐, and 4‐factor interactions on N mineralization were statistically significant at P=0.05. Based on w ², incubation time (T), and incorporation rate (R) were the two most important factors affecting N mineralization. The amount of N mineralized increased exponentially with increasing time and linearly with the incorporation rate. In addition, the incorporation of plant material not only increased potentially mineralizable N by as much as 5.1 times but also accelerated N mineralization in soil by increasing the N mineralization rate constant 75%.     

Ionic balance,biomass production,and organic nitrogen as affected by salinity and nitrogen source in annual ryegrass

Studies on the effects of salinity and nitrogen (N) fertilization on ionic balance, biomass, and organic N production of annual ryegrass (Lolium multiflorum Lam.) were conducted. Plants grown in sand were irrigated with nutrient solution with an electrical conductivity of 2 or 11.2 dS#lbm^‐1, and N in the form of sodium nitrate (NaNO₃), ammonium nitrate (NH₄NO₃), or ammonium sulfate [(NH₄)₂SO₄] ranging from 0.5 to 9.0 mM. Salinity increased the concentration of total inorganic cations (C) in plants and specifically sodium (Na) by more than 3‐fold higher in plants grown at high salinity as compared with plants at low salinity. Sodium (Na) concentration in roots was higher than in shoots irrespective of the salinity level, suggesting a restriction of Na transport from roots to shoots. The concentration of total inorganic anions (A) increased with salinity and when plants were supplied with nitrate (NO₃), salinity increased the concentrations of NO₃ and chloride (Cl) in plants. Increasing salinity and N concentration in the growth medium increased organic anions concentration in plants, estimated as the difference between C and A. The effect of different N sources on C‐A followed the order: NH₄NO₃ > NO₃ > ammonium (NH₄). The base of organic anions and inorganic ions with salinity contributed significantly to the osmotic potential of plants shoots and roots. Changes in C affected N and organic acids metabolism in plants, since C were highly correlated (p=0.0001) with C‐A and organic N (N_org) concentrations regardless of the salinity level or N source in the nutrient solutions. A high and positive linear dependency was found between N_org and C‐A in plants grown at high and low salinity levels and different N sources, pointing out the close relationship between N_org and organic anions on metabolism under these conditions. The amount of biomass produced was correlated positively with organic anion concentration in plants exposed to different salinity levels. Plant biomass increased with N concentration in the nutrient solution regardless of the salinity level applied. Biomass accumulation decreased while N_org concentration increased with salinity. Organic N content remained unaffected in plants exposed to salinity when grown in N less than 9.0 mM.     

The Effects of Sulphur Application on Yield,Sulphur Content and N/S-Ratio of Grasses for Silage at Six Sites in Finland

Abstract

The effects of sulphur (S) fertilization on forage production, sulphur content and N/S ratio of perennial timothy-meadow-grass (Phleum pratens L.- Festuca pratensis Hudson) and cocksfoot-dominant (Dactylis glomerata L.) swards cropped for one to three years were measured under a silage-cutting regime at six sites in Finland. Soil sulphur status ranged from poor/adequate (fine sand) to good (organic soils). Plant growth responses to supplementary sulphur were small, inconsistent and statistically insignificant. The supplementary S-fertilization increased the sulphur content of forage and decreased N/S-ratios at all sites. However, even in low-S fertilized plots the average sulphur content was very seldomly less than 0.2% on a dry matter (DM) basis, which has been assumed to be an adequate concentration in several foreign studies. High N/S ratios (> 14) were rare. The sulphur content of DM depended more significantly on growth stage and grass species than on supplementary sulphur. According to the results of these experiments, NPKS fertilizers contain sufficient amounts of sulphur to ensure both a good quality and a high yield of grass silage.     

Sulfur mineralization in two soils amended with organic manures,crop residues,and green manures

The mineralization of sulfur (S) was investigated in a Vertisol and an Inceptisol amended with organic manures, green manures, and crop residues. Field‐moist soils amended with 10 g kg^—1 of organic materials were mixed with glass beads, placed in pyrex leaching tubes, leached with 0.01 M CaCl₂ to remove the mineral S and incubated at 30 °C. The leachates were collected every fortnight for 16 weeks and analyzed for SO₄‐S. The amount of S mineralized in control and in manure‐amended soils was highest in the first week and decreased steadily thereafter. The total S mineralized in amended soils varied considerably depending on the type of organic materials incorporated and soil used. The cumulative amounts of S mineralized in amended soils ranged from 6.98 mg S (kg soil)^—1 in Inceptisol amended with wheat straw to 34.38 mg S (kg soil)^—1 in Vertisol amended with farmyard manure (FYM). Expressed as a percentage of the S added to soils, the S mineralized was higher in FYM treated soils (63.5 to 67.3 %) as compared to poultry manure amended soils (60.5 to 62.3 %). Similarly the percentage of S mineralization from subabul (Leucaena leucocephala) loppings was higher (53.6 to 55.5 %) than that from gliricidia (Gliricidia sepium) loppings (50.3 to 51.1 %). Regression analysis clearly indicated the dependence of S mineralization on the C : S ratio of the organic materials added to soil. The addition of organic amendments resulted in net immobilization of S when the C : S ratio was above 290:1 in Vertisol and 349:1 in Inceptisol. The mineralizable S pool (S_o) and first‐order rate constant (k) varied considerably among the different types of organic materials added and soil. The S_o values of FYM treated soils were higher than in subabul, gliricidia, and poultry manure treated soils.     

Carbon and nitrogen mineralization in acidic, limed and calcareous agricultural soils: Apparent and actual effects

Soil pH and calcium carbonate contents are often hypothesized to be important factors controlling organic matter turnover in agricultural soils. The aim of this study was to differentiate the effects of soil pH from those related to carbonate equilibrium on C and N dynamics. The relative contributions of organic and inorganic carbon in the CO₂ produced during laboratory incubations were assessed. Five agricultural soils were compared: calcareous (74% CaCO₃), loess (0.2% CaCO₃) and an acidic soil which had received different rates of lime 20 years ago (0, 18 or 50 t ha⁻¹). Soil aggregates were incubated with or without rape residues under aerobic conditions for 91 days at 15 °C. The C and N mineralized, soil pH, O₂ consumption and respiratory quotient (RQ=ΔCO₂/ΔO₂) were monitored, as well as the δ¹³C composition of the evolved CO₂ to determine its origin (mineral or organic). Results showed that in non-amended soils, the cumulative CO₂ produced was significantly greater in the limed soil with a pH>7 than in the same soil with less or no lime added, whereas there was no difference in N mineralization or in O₂ consumption kinetics. We found an exponential relationship between RQ values and soil pH, suggesting an excess production of CO₂ in alkaline soils. This CO₂ excess was not related to changes in substrate utilization by the microbial biomass but rather to carbonates equilibrium. The δ¹³C signatures confirmed that the CO₂ produced in soils with pH>7 originated from both organic and mineral sources. The contribution of soil carbonates to CO₂ production led to an overestimation of organic C mineralization (up to 35%), the extent of which depended on the nature of soil carbonates but not on the amount. The actual C mineralization (derived from organic C) was similar in limed and unlimed soil. The amount of C mineralized in the residue-amended soils was ten times greater than in the basal soil, thus masking the soil carbonate contribution. Residue decomposition resulted in a significant increase in soil pH in all soils. This increase is attributed to the alkalinity and/or decarboxylation of organic anions in the plant residue and/or to the immobilization of nitrate by the microbial biomass and the corresponding release of hydroxyl ions. A theoretical composition (C, O, H, N) of residue and soil organic matter is proposed to explain the RQ measured. It emphasizes the need to take microbial biomass metabolism, O₂ consumption due to nitrification and carbon assimilation yield into account when interpreting RQ data.     

An evaluation of chemical methods for extracting copper from rice soils

Abstract

Rice (Oryza sativaL. CV. Lemont) was grown on 19 soils, and eight extractants were evaluated for determining the availability of Cu to rice plants. Correlation analyses were employed as criteria for evaluating methods that would provide the best index of Cu availability. The order of removal of Cu from soils was: 0.5NHC1 + 0.05NA1C1₃> 0.5NHNO₃> 0.5 N HC1 > EDTA + NH₄OAc > 0.1NHC1 > EDTA + (NH₄)₂CO₃? DTPA‐TEA, pH 7.3 >>> 1 N NH₄0Ac, pH 4.8.

Uptake of Cu by rice plants was significantly correlated with soil Cu. Among the eight extractants evaluated, Cu extracted with DTPA‐TEA, pH 7.3 was better related to the concentration (r = 0.563 ) and uptake (r = 0.673 ) of Cu by rice plants grown on the soils with different chemical and physical properties.

A significant negative correlation was found between the concentration of Cu in rice plants and the organic matter content of the soils. Each one percent increase in the organic matter of the soils resulted in a corresponding decrease of approximately one mg/kg in the concentration of Cu in the rice‐plant tissue. Multiple regressions of extractable Cu by eight methods with soil organic matter content accounted for from 53.4 to 70.0% of the variations in the prediction of the concentration of Cu in the rice plants. Combinations of other soil chemical properties measured with extractable Cu did not significantly improve the predictability     

Correlation among microbial biomass s,soil properties,and other biomass nutrients

The soil physicochemical characteristics and amounts of microbial biomass C, N, and S in 19 soils (10 grassland, 2 forest, and 7 arable soils) were investigated to clarify the S status in granitic regosols in Japan, in order to determine the relationships between biomass S and other soil characteristics and to estimate approximately the annual Sand N flux through the microbial biomass. Across the sites, the amount of biomass C ranged from 46 to 1,054, biomass N from 6 to 158, and biomass S from 0.81 to 13.44 mg kg_-1 soil with mean values of 438.8, 85.8, and 6.15 mg kg_-1 soil, respectively. Microbial biomass Nand S accounted for 3.4–7.7% and 1.1–4.0% of soil total Nand S, respectively. The biomass C: N, C : S, and N : S ratios varied considerably across the sites and ranged from 3.0–10.4, 32.5–87.7, and 5.0–18.8, respectively. Microbial biomass S was linearly related to biomass C and biomass N. The regression accounted for 96.6% for biomass C and 92.9% for biomass N of the variance in the data. The amounts of biomass C, N, and S were positively correlated with a number of soil properties, particularly with the contents of organic C, total N, SO₄-S, and electrical conductivity and among themselves. The soil properties, in various linear combinations showed a variability of 84–97% in the biomass nutrients. Stepwise multiple regression indicated that biomass C, N, and S were also dependent on SO₄-S as a second factor of significance which could limit microbial growth under the conditions prevailing at the study sites. Annual flux of Nand S was estimated through the biomass using the turnover rates of 0.67 for Nand 0.70 for S to be approximately 129 kg Nand 9.7 kg S ha^-1 y^-l, respectively, and was almost two times higher in grassland than arable soils.     

Immobilized-S, microbial biomass-S and soil arylsulfatase activity in the rhizosphere soil of rape and barley as affected by labile substrate C and N additions

Bulk and rhizosphere soil of rape and barley grown in a calcareous soil were pre-incubated for 7 days at 20 °C with Na₂³⁵SO₄ to partially label soil organic S. The soils were then incubated for 7 days more with increasing levels of two C sources as organic acids (succinic and malic acids) and as glucose (from 0 to 640 mg C kg⁻¹ soil) with or without increasing levels of N (from 0 to 15 mg N kg⁻¹ soil) in the form of ammonium nitrate, in order to mimic rhizodeposition inputs into soil. A second incubation experiment with a single highest dose of the used substrates was undertaken and two destructive soil samplings on days 17 and 35 were carried out. Both incubation experiments showed the intensities of S immobilization in the order: barley rhizosphere>rape rhizosphere>bulk soil. Glucose addition generated positive S priming effects in all studied soils after one week of incubation. Significant correlation coefficients were observed between immobilized-S and microbial biomass-S (r=0.95,p<0.001), arylsulfatase activity (ARS) and microbial biomass-S (r=0.65,p<0.05) on day 17 but not on day 35, whereas significant correlation coefficients were found between arylsulfatase activity and immobilized-S at both days 17 (r=0.79,p<0.01) and 35 (r=0.75,p<0.01). A marked decline of biomass-S noted in substrate-amended treatments at day 35 suggests a quick turnover of this compartment followed by its incorporation into the organic S. Finally, with organic acids high values of ARS per unit of biomass-S were recorded over the two studied dates in the rhizosphere soil of rape. It is concluded that the rhizosphere microbial biomass under rape exhibited more efficient arylsulfatase activity and hence greater turnover of organic S than that under the barley rhizosphere soil.     

NITROGEN–PHOSPHORUS–POTASSIUM EFFECTS ON FORMS OF SULFUR IN LEAVES AND FRUITS OF CUCUMBER

ABSTRACT

The impact that nitrogen (N), phosphorus (P), and potassium (K) application rates on the sulfur (S) fractions in leaves and fruits of greenhouse-grown cucumbers plants (Cucumis sativus L. cv. Brunex) are presented. The treatments were as follows: N (N1=5 g NO₃NH₄/m², N2=10 g NO₃NH₄/m², N3=20 g NO₃NH₄/m², N4=40 g NO₃NH₄/m²), two levels of P (P1=8 g H₃PO₄/m² and P2=16 g H₃PO₄/m²), and two levels of K (K1=20 g K₂SO₄/m² and K2=40 g K₂SO₄/m²). The foliar and fruit contents were determined for total S, organic S and sulfate. The influence of the N treatments on the total S (St: organic S +sulfate) concentration, proved significant, showing a progressive increase in the leaf and fruit concentrations. In the leaves, the P slightly diminished the St concentration but values in the fruits did not appreciably differ from control. The K dosage did not cause the St concentration to differ from that of P, although in the fruit a slightly lower St concentration appeared in the K2 treatment. The response of the organic-S concentration in the leaves resembled that of St, and thus organic S should not be used as a diagnostic method for S status. In the relationship SO₄ ^2-/St, the SO₄ ^2- concentration proved more influential than did the St form, providing a more accurate representation of the potential status of this nutrient in the plant.     

Surface runoff phosphorus (P) loss in relation to phosphatase activity and soil P fractions in Florida sandy soils under citrus production

Phosphorus losses by surface runoff from agricultural lands have been of public concern due to increasing P contamination to surface waters. Five representative commercial citrus groves (C1-C5) located in South Florida were studied to evaluate the relationships between P fractions in soils, surface runoff P, and soil phosphatase activity. A modified Hedley P sequential fractionation procedure was employed to fractionate soil P. Soil P consisted of mainly organically- and Ca/Mg-bound P fractions. The organically-bound P (biological P, sum of organic P in the water, NaHCO₃ and NaOH extracts) was dominant in the acidic sandy soils from the C2 and C3 sites (18% and 24% of total soil P), whereas the Ca/Mg-bound P (HCl-extractable P) accounted for 45-60% of soil total P in the neutral and alkaline soils (C1, C4 and C5 soils). Plant-available P (sum of water and NaHCO₃ extractable P fractions) ranged from 27 to 61 mg P kg⁻¹ and decreased in the order of C3>C4>C1>C2>C5. The mean total P concentrations (TP) in surface runoff water samples ranged from 0.51 to 2.64 mg L⁻¹. Total P, total dissolved P (TDP), and PO₄³⁻-P in surface runoff were significantly correlated with soil biological P and plant-available P forms (p<0.01), suggesting that surface runoff P was directly derived from soil available P pools, including H₂O- and NaHCO₃- extractable inorganic P, water-soluble organic P, and NaHCO₃- and NaOH-extractable organic P fractions, which are readily mineralized by soil microorganisms and/or enzyme mediated processes. Soil neutral (55-190 mg phenol kg⁻¹ 3 h⁻¹) and natural (measured at soil pH) phosphatase activities (77-295 mg phenol kg⁻¹ 3 h⁻¹) were related to TP, TDP, and PO₄³⁻-P in surface runoff, and plant-available P and biological P forms in soils. These results indicate that there is a potential relationship between soil P availability and phosphatase activities, relating to P loss by surface runoff. Therefore, the neutral and natural phosphatase activities, especially the natural phosphatase activity, may serve as an index of surface runoff P loss potential and soil P availability.     

Layer and broiler poultry manure as nitrogen fertilizer sources for cabbage production

Abstract

Floor litter from one‐year‐old laying hens (LHM) and from eight‐week‐old broiler chickens (BCM) were incorporated in the soil of two fields and evaluated as nitrogen (N) sources for cabbage production on a non nutrient‐depleted soil. LHM had 3.4% moisture, 3.84% N and 3.41% phosphorus (P). BCM had 2.3% moisture, 4.46% N and 2.19% P. Field 1 recieved 2.4 t/ha BCM, 3.0 t/ha LHM, whereas Field 2 recieved 4.8 t/ha BCM and 6.1 t/ha LHM. Also, each field received ammonium sulfate [(NH₄)₂SO₄] at a N rate of 100 kg/ha and an unfertilized control treatment. The manure was applied one week before cabbage transplanting on 18 May 1992. Ammonium sulfate was applied in two equal split applications during the growing season. Leaf nitrate‐nitrogen (NO₃‐N) was higher at harvest in plants receiving the higher manure rate than in other treatments (P<0.05). Leaf phosphate (PO₄‐P) was higher in early season in plants receiving LHM at both Tates than in other treatments. Soil BD, EC, NO₃‐N, and P at harvest were not affected by the treatments (P>0.05). Soil pH was reduced by the LHM in comparison to other treatments (P<0.05). Yield was comparable among all treatments (P>0.05) . It may be concluded that low application rates of LHM and BCM are equally effective in supplying the N requirements of cabbage, with BCM recommended when only N is limiting, and LHM when P is limiting.     

Preparation and characterization of model humic polymers containing organic phosphorus

The nature of organic P in soil organic matter was studied by evaluating the incorporation of serine, phosphoserine, ethanolamine, phosphoethanolamine and glycerophosphate into model humic polymers prepared by chemical oxidation of polyphenols. Elemental and functional group analysis indicated that the composition of model humic polymers ranged as follows: organic C, 50.6–56.8%; total acidity, 7.86–11.87m-equiv g^?1; carboxyl, 1.42–2.00 m-equiv g^?1; total hydroxyl, 6.79-10.0 m-equiv g^?1; ash, 6.4–13.9%; E₄/E₆ ratio, 5.34–6.19; organic N, 0.70–1.65% and organic P, 0.254–0.942%. These values are within the ranges reported for soil humic substances. The only non-phenolic compounds incorporated into model humic polymers were those containing free amino groups. The P content of model polymers was not increased by the presence of KH₂PO₄, glycerophosphate, serine or ethanolamine whereas phosphoserine and phosphoethanolamine resulted in model polymers containing 0.254 and 0.942% P, respectively. Further characterization studies of the model polymer containing phosphoethanolamine (HA-PE) showed that most of the C (83.2%), N (79.8%) and P (75.3%) was in the humic acid fraction. Gel filtration of HA-PE showed that 0.5% of the polymer was present in high molecular weight (mol. wt) components (mol. wt > 100,000) and 74.8% of the polymer was in two components of mol. wt 10,000–50,000. The majority of the organic P in HA-PE was associated with the medium molecular weight fractions (79.2%) while 16.8% of the P was associated with materials possessing mol. wt < 10,000. Attempts to demonstrate the presence of organic P functional groups contained in HA-PE by infrared spectroscopy was limited by the relatively small amounts of organic P incorporated into the model humic polymers. The results obtained show that a portion of the unidentified organic P in soil humic substances may arise from the incorporation of organic compounds containing both amino and phosphate ester functional groups during oxidative polymerization of polyphenols.     

Effect of Crop Rotations and Continuous Fertilization on the Status of Silicon (Si) Available in Soil in a 97-Year Permanent Experiment

ABSTRACT

This work aims to study the status of silicon (Si) as a plant nutrient in the soil of Bahtim long-term field experiment in Egypt under the effect of crop rotations system and continuous fertilization. The experiment has been set up since 1912 based on two main factors: (1) crop rotations: mono-cropping (MC), two-year rotation (2Y-R), and three-year rotation (3Y-R), and (2) Fertilization: mineral nitrogen N, phosphorus P, potassium K, and organic farmyard manure FYM. Available N, P, K, and Si in soil were estimated. Productivity of soil was evaluated using Berseem (Trifolium alexndrinum L.) cultivated and harvested in 2019. The plant-available Si (PAS) in soil decreased significantly compared to the control C in case of MC by 70.26%, 2Y-R by 85.09%, and 3Y-R by 92.65% in the direction of N > NP > NPK. Mineral fertilization decreased the PAS significantly by 12.84% N, 29.52% NP, 78.45% NPK compared to the control C in the order of MC > 2Y-R > 3Y-R. Berseem yield (t ha^?1) increased significantly compared with the control C following the order C < N < NP < NPK. The most significant increase in the yield was recorded for the NPK treatments by 224.04%, and 200% in case of MC, 2Y-R, 3Y-R, respectively.