Inorganic P Research Articles

Effect of amending high phosphorus soils with flue-gas desulfurization gypsum on plant uptake and soil fractions of phosphorus

Flue gas desulfurization (FGD) gypsum, a coal combustion by-product, can be used to decrease water-extractable soil P, thereby lowering the potential for P export to surface waters. This decrease results from a conversion of loosely bound inorganic P (IP) which is readily desorbable to water, to less soluble Al- and Fe-bound IP and, to a lesser extent, calcium-bound IP pools. Although this conversion has little effect on predictors of plant-available soil P (e.g., Mehlich-3 P), little is known about the plant uptake of P over several growth cycles after high P soils are amended with FGD. In a greenhouse experiment, we measured P uptake by ryegrass (Lolium perenne) using a modified Stanford–Dement procedure (three growth cycles), and the extent to which IP was being removed from each soil IP fraction (Hedley fractionation), for three soils treated with FGD gypsum (equivalent to 22.4 Mg ha−1). Treatment with FGD decreased water extractable soil P 38 to 57%, but had little effect on Mehlich-3 soil P. During the first growth cycle, the shift from resin IP to less available Al, Fe, and Ca IP remained stable. Repeated growth cycles of ryegrass removed resin IP and thus, had a continued effect on lowering water-extractable P. After three growth cycles and harvests, ryegrass dry-matter production was not affected by FGD treatment (P > 0.05), although cumulative P uptake (20%) and P concentration of ryegrass tops (25%) were greater in FGD treated than untreated soils. Our results confirm that treatment of high P soils with FGD gypsum decreases water-extractable P by conversion to soil IP fractions that are stable with time, does not decrease plant production, and suggests that the potential for P export in surface runoff may be reduced for several years.

PHOSPHORUS PARTITIONING AND PHOSPHATASE ACTIVITY IN SEMI-ARID REGION SOILS UNDER INCREASING CROP GROWTH INTENSITY 1

Reduction in the use of fallow in traditional wheat-fallow cropping systems, along with other management changes such as reduced tillage, raise questions about nutrient management, particularly phosphorus (P) management, in such soils. Phosphorus is focused on because of its low soil mobility and its common application in wheat cropping systems. Consequently, we initiated a study with the following objectives: (i) Measure changes in soil available P status during the fallow year under two different cropping intensities; (ii) Determine differences in P status with soil depth and topographic position; (iii) Relate changes in P fractions (organic, inorganic) to P availability; and (iv) Relate P availability (as measured by Bray and Kurtz [B&K] extraction) to soil phosphatase activity. We sampled soils by depth, topographic position, and season during the fallow year in farmers’ fields used for wheat-fallow (w-f) or wheat-proso millet-fallow (w-m-f) cropping systems located near Sidney, Nebraska. Soils were analyzed for B&K-P, total P (TP), inorganic P (IP), organic P (OP), organic matter (OM), and phosphatase activity. Soils under w-m-f were up to 5 mg P kg−1 soil higher in B&K-P than those under w-f, but differences were not significant. Soils at footslope positions were significantly higher in OP, IP, TP, OM, and phosphatase activity, probably because of a combination of deposition of eroded soil and higher average soil moisture content. Differences in P-related properties across seasons were inconsistent. B&K-P was strongly correlated to phosphatase activity, OM, IP, and TP (all P < 0.0001). The general absence of differences in any measured quantity between cropping systems suggests that cropping intensity can be increased in semiarid climates such as the study site, at least over the short-term, without concerns of inducing P deficiencies. Phosphatase activity, although related to P availability, does not offer greater benefits in predicting soil P supply than established soil tests.

Moderately resistant phosphorus forms in subtropical ultisol of Argentina

The efficiency of phosphorus (P) fertilization may be improved through knowledge of soil P fraction changes with time. This study examined: i) the distribution of P fractions according to Hedley's fractionation scheme and ii) the sequential changes in soil organic P (OP) and inorganic P (IP) in a typical Kandihumult, under favorable conditions for mineralization and under depletion conditions, with and without P fertilization. Soil P fractions considered were IP‐resin, IP‐ and OP‐bicarbonate, and IP‐ and OP‐hydroxide. The soil is characterized by the predominance of moderately resistant P, in organic and inorganic fractions. In the presence of favorable conditions for mineralization, a substantial decrease in moderately resistant organic P was observed, enhanced even more by fertilizer incorporation. The decrease of total extracted P (TPe) before depletion situations was mainly produced in the moderately resistant fraction, that registered a decrease of 23% (of this value 65% were due to OP). The main fate of the fertilization, in both situations (active mineralization as well as depletion) was moderately resistant inorganic phosphate.

Atmospheric input of nitrogen and phosphorus to the Southeast Mediterranean: Sources, fluxes, and possible impact

Estimates of the sources and wet deposition fluxes of inorganic nutrients (PO43−, NO3−, NO2−, NH4+) have been made using a long‐term wet atmospheric deposition measurement at three sites along the Mediterranean coast of Israel. The nutrient composition in rainwater indicated a dominant anthropogenic source for NO3− and NH4+ and a continental, natural, and anthropogenic, rock/soil source for PO43−. The calculated long‐term dissolved inorganic N (IN) and inorganic P (IP) fluxes were 0.28 and 0.009 g m−2 yr−1 to the coastal zone and estimated as 0.24 and 0.008 g m−2 yr−1 to the Southeast (SE) Mediterranean, with a possible increasing pattern of the annual dissolved IN fluxes. Concentration of total and seawater leachable IP (LIP) from dust was examined on 20 Whatman 41 filters collected during 1996. The mean total IP concentration in dust was 0.13 ± 0.11% (geomean = 0.09%), with a mean of 387 ± 205 μg IP per g of dust leached by seawater. LIP from dust varies between 6 and 85% (mean of 38%) of the dry total IP. Dust of desert‐type (Saharan) events exhibited lower LIP solubility in seawater (∼25%, median) than air masses of European origin (∼45%, median). The calculated ratio of wet deposition to total (wet and dry) deposition here of 0.2 showed the importance of dry deposition of P in the SE Mediterranean basin compared to atmospheric inputs into the northwestern basin. The total IP and seawater LIP fluxes from dry deposition were estimated as 0.04 and 0.01 g m−2 yr−1, respectively. Atmospheric inputs of bioavailable N and P represent an imbalanced contribution to the new production of 8–20 and 4–11%, respectively, and reinforce the unusual N:P ratios (∼27) and possible P limitation in the SE Mediterranean.

Frações fosfatadas em mudas de Eucalyptus

Com o objetivo de avaliar os teores e o efeito do tempo de omissão de fósforo nas frações de P em diferentes espécies de eucalipto, instalou-se um experimento em condições controladas no Departamento de Solos da Universidade Federal de Viçosa - UFV, no período de fevereiro a julho de 1993. Avaliou-se, em câmara de crescimento, o comportamento das frações fosfatadas em mudas das seguintes espécies de eucalipto: E. clöeziana ,E. grandis ,E. pellita ,E. pilularis e E. urophylla, quando submetidas à omissão de P. Foi fornecida às plantas uma solução nutritiva com elevado teor de P (8 mg L-1 de P) por vinte e quatro horas. Após esse período, eliminou-se o P da solução nutritiva e analisaram-se as frações de P total solúvel em ácido (Pts), fósforo inorgânico (Pi) e fósforo orgânico (Po), nos tempos de 0, 10 e 20 dias após a omissão do nutriente. Os compartimentos analisados foram as partes apicais e basais de folhas e raízes. A omissão do P da solução nutritiva causou queda no conteúdo de Pts e Pi em todas as espécies, embora em diferente magnitude. E. clöeziana apresentou o maior conteúdo de Pts. Com o aumento do tempo de omissão, as espécies de eucalipto apresentaram redução no percentual de participação do Pi em relação ao Pts, seguido de maior participação relativa do Po nos diversos compartimentos analisados. E. pellita e E. grandis apresentaram um padrão mais homogêneo de comportamento das frações fosfatadas com o tempo de omissão, quando comparadas às outras espécies. Entretanto, essas espécies apresentaram baixos teores de Pi já aos 10 dias de omissão de P, indicativo de um baixo "poder tampão interno de Pi" em relação às outras espécies avaliadas.

Phosphorus fractions in argentine soils of different pedogenesis

Abstract The distribution of phosphorus (P) in different organic and inorganic fractions was examined in five Argentinean soils of different pedogenesis. Soils were sequentially extracted to determine resin‐P, bicarbonate‐P, and hydroxide‐P fractions. Inorganic P (IP) predominated in all soils, specially moderately resistant IP (MRIP) in Entisol, Vertisol, and Ultisol. Both MRIP and labile IP (LIP) were important in Mollisol. Organic P (OP) was at a lower concentration in all soils and moderately resistant OP (MROP) was highest in all soils, except for the Mollisol. In intermediate evolution soils, labile P (LP) was very important, Mollisol had the highest value of LP%, and the lowest was for the Ultisol, demonstrating greater dynamics of P fractions in the Mollisol, soils of high productivity in the Pampean Prairie.

Bioavailable phosphorus dynamics in agricultural soils and effects on water quality

The transport of bioavailable phosphorus (BAP, i.e., algal available) in agricultural runoff can accelerate freshwater eutrophication. As procedural and theoretical limitations have restricted BAP estimation in agricultural soils and runoff, a routine method was developed using iron oxide-impregnated paper strips (Fe-oxide strips) as a sink for BAR Fe-oxide strips were used to investigate the amounts and seasonal dynamics of BAP in 12 Oklahoma soils over 2 years and the effect of agricultural management on BAP loss in runoff from these 12 and 8 additional sites over 4 years. The sites involved native grass, wheat ( Triticum aestivum L.), sorghum [ Sorghum bicolor (L.) Moench.], and peanut ( Arachis hypogaea L.). The strip P content of unfertilized soils was higher in winter (October–March; 10–19 mg kg −1) than spring months (May–June; 3–6 mg kg −1). For the P-fertilized soils, the strip P content increased from 8–17 mg kg −1 prior to P application (20–25 kg ha −1 yr −1 to 33–42 mg kg −1 immediately following application. Seasonal dynamics of strip and organic (OP) and inorganic P (IP) fractions indicated mineralization of moderately labile OP, as a function of phosphatase enzyme activity, and release of moderately labile IP and fertilizer P, as a function of P sorption capacity; these are the major processes controlling the strip P content of unfertilized and fertilized soil, respectively. Dissolved organic P did not reduce the efficiency of IP sorption by the Fe-oxide strips and removal of P from the strips by NaOH rather than H 2S0 4 minimized hydrolysis of OP sorbed on the strip. The loss of BAP in runoff was a function of watershed management. Over the 4-yr study, BAP losses increased in the order reduced till (98 g ha −1 yr −1), native grass (160 g ha −1 yr −1), no till (382 g ha −1 yr −1), and conventional till (678 g ha −1 yr −1). Although the total P loss was 93% lower from no till than conventional till, 73% was bioavailable for no till compared to only 28% for conventional till. Clearly, strip P is a dynamic soil property, which, along with watershed management, can influence the bioavailability of P loss in runoff. Thus, the BAP content of runoff in conjunction with runoff and erosion potential may provide a more reliable index of the trophic response of receiving water bodies than dissolved or total P.

NITROGEN AND PHOSPHORUS FORMS IN SOILS RECEIVING MANURE

Increasing production of beef, poultry, and swine from confined feeding operations in the Southern Plains necessitates that larger amounts of mannure be applied to limited areas of agricultural land. If long-term manure applications of nitrogen (N) and phosphorus (P) in manure exceed crop removal, the accumulation of soil N and P can result in levels that pose a problem of concern to both surface and groundwater resources. We investigated the effect of beef feedlot manure, poultry litter, and swine slurry applications (100-1000 kgN and 37-270 kgP ha −1 yr −1 ) for up to 35 years on the forms of N and P in 20 soils from the Southern Plains. Manure applications increased amounts of organic soil N but had little influence on the distribution or availability of N forms measured. In contrast with N, manure increased available inorganic P (IP) fractions 15 to 187 mg kg −1 (bicarbonate extractable). Although manure also increased labile bicarbonate extractable organic P (OP) on average 162%, there was a general shift from OP dominace in untreated soils (64%) to IP in treated soils (60%). The major portion of this IP increase was Ca-bound (HCl extractable). The large amounts of Ca added in manure (2-60 g Ca kg −1 ) tended to dominate inorganic P availability reactions in manure-treated soils relative to untreated soils, even with soils of pH 6.0. Thus, current soil P tests, particularly acid-based extractants (Bray 1 and Mehlich 3), may overestimate soil P levels available for plant uptake or transport in runoff

Effect of Rainfall and Subsequent Drying on Nitrogen and Phosphorus Changes in a Dryland Fallow Loam

Abstract36Chloride placed at 15‐ or 30‐cm depth in 15‐cm diameter cylinders of fallow loam was leached to at least 50 cm during and immediately following rainfall &gt; 1.75 cm. As the soil dried following rainfall 36Cl moved upwards. Nitrate content of leachates from a lysimeter experiment corroborated the leaching aspects of the 36Cl expcriment.In the 0‐ to 2.5‐cm segment of a second‐year fallow loam which was sheltered from rainfall, moisture was below the wilting percentage and NO3−N and bacterial numbers declined as the soil gradually dried out. In the 2.5‐ to 15‐cm segment, moisture was in the available range, yet moisture and NO3‐N changes were small.In unsheltered fallow loam, NO3‐N production in the 0‐ to 2.5‐cm depth was primarily a function of soil moisture change: ΔNO3−N = −0.55 − 1.11 ΔM, (r = −0.94**), and ΔNO3‐N = −0.45 ‐ 0.56 ΔM, (r = −0.81*) in the second‐ and first‐year fallow, respectively; (M = % moisture and Δ = daily change). The increase in NO3‐N during drying seemed to be more a result of upward movement than of nitrification. There was a negative linear relationship between ΔNO3‐N and Δ bacteria in the 0‐ to 2.5‐cm soil segment. Sodium bicarbonate soluble inorganic P (IP) generally exceeded NaHCO3 soluble organic P (OP). In second‐year fallow, P was unaffected by environmental conditions. In first‐year fallow ΔIP in the 0‐ to 2.5‐cm segment was directly related to rainfall (r = 0.98**), to ΔM (r = 0.97**), and to Δ bacteria (r = 0.88**), and inversely related to ΔNO3‐N (r = −0.76*).