Total P Content Research Articles

Characterization and Risk Assessment of Nutrient and Heavy Metal Pollution in Surface Sediments of Representative Lakes in Yangxin County, China

Increased urbanization and industrialization globally have led to the widespread pollution of water bodies (e.g., lakes) by heavy metals (HMs) and nutrients. These pollutants accumulate in water and surface sediments, posing risks to both aquatic organisms and human health. In November 2022, surface sediment samples from three lakes—Lianhua Lake, Mati Lake, and North Lake—were collected to assess nutrient (nitrogen and phosphorous) and HM content. Total N (TN), total P (TP), and HM concentrations were analyzed. The pollution status was evaluated using comprehensive pollution index (FF) methods and the potential ecological risk index (RI) (Eri). The results were as follows: (1) Variations in nutrient and HM contents were observed among the three lakes. Lianhua Lake exhibited the highest average TN content (1600 mg/kg), while North Lake had the highest average TP content (2230 mg/kg). The average concentrations of Cd, Hg, and As in the surface sediment surpassed the soil background values of Hubei Province, reaching 1.41, 2.74, and 1.76 times the background values, respectively. Notably, Hg exceeded the standard in Lianhua Lake by 3.39 times, followed by North Lake (2.52 times) and Mati Lake (2.24 times). (2) The FF and potential Eri revealed that the average RI values for Mati Lake, North Lake, and Lianhua Lake were 106.88, 126.63, and 162.18, respectively. These indices categorized the ecological risk levels as moderate, while nutrient salts in the surface water reached a severe pollution level. (3) Correlation and PCA indicated that Cu, Pb, Cd, and Ni were linked to mineral smelting, aquaculture feed, and agricultural fertilizers. Hg and nutrient salts originated from atmospheric deposition of surrounding domestic waste water and traffic exhaust gases. Agricultural activities seemed to contribute to As concentration in the lakes, while Cr has its main origin in the weathering of the rock matrix.

Phosphorus absorption kinetics and exudation strategies of roots developed by three lupin species to tackle P deficiency.

Different lupin species exhibited varied biomass, P allocation, and physiological responses to P-deprivation. White and yellow lupins had higher carboxylate exudation rates, while blue lupin showed the highest phosphatase activity. White lupin (Lupinus albus) can produce specialized root structures, called cluster roots, which are adapted to low-phosphorus (P) soil. Blue lupin (L. angustifolius) and yellow lupin (L. luteus), which are two close relatives of white lupin, do not produce cluster roots. This study characterized plant responses to nutrient limitation by analyzing biomass accumulation and P distribution, absorption kinetics and root exudation in white, blue, and yellow lupins. Plants were grown in hydroponic culture with (64µM NaH2PO4) or without P for 31days. Under P limitation, more biomass was allocated to roots to improve P absorption. Furthermore, the relative growth rate of blue lupin showed the strongest inhibition. Under + P conditions, the plant total-P contents of blue lupin and yellow lupin were higher than that of white lupin. To elucidate the responses of lupins via the perspective of absorption kinetics and secretion analysis, blue and yellow lupins were confirmed to have stronger affinity and absorption capacity for orthophosphate after P-deprivation cultivation, whereas white lupin and yellow lupin had greater ability to secrete organic acids. The exudation of blue lupin had higher acid phosphatase activity. This study elucidated that blue lupin was more sensitive to P-scarcity stress and yellow had the greater tolerance of P-deficient condition than either of the other two lupin species. The three lupin species have evolved different adaptation strategies to cope with P deficiency.

An analysis of long-term Everglades Stormwater Treatment Areas performance using structural equation models

Phosphorus (P) retention in Stormwater Treatment Areas (STAs) is influenced by various external and internal variables, making it necessary to employ multivariate techniques to understand the complex relationships among them. This study used 14 years of monthly data from four STAs (STA-1E, -1W, −2, and − 3/4) to explore the factors influencing long-term STA performance and function related to P retention. Structural Equation Model (SEM) with predictive variables of inflow total P (TP), total nitrogen (TN) and calcium (Ca) concentration, hydraulic loading rate (HLR), and water pH and temperature was applied to evaluate similarities and differences among individual STA performance. The SEM results suggested an improvement in operational performance of STAs over time. All models explained a substantial portion of the variation in retention rate of TP (R2 > 0.63), but only a small portion of the variation in outflow TP concentration (R2 < 0.24). Notable differences were observed among the four STAs. The relationship between inflow and outflow TP concentration differed among the STAs. Furthermore, inflow TN concentration was positively correlated with the TP retention rate in STA-1W, and outflow TP concentration in STA-2, while the co-precipitation of P with Ca likely played a critical role in STA-3/4. These findings highlight the complexity of P removal in STAs and emphasize the need for site-specific management strategies. Further studies should consider incorporating long-term observation of key vegetation and soil variables (e.g. vegetation coverage and soil TP content, etc.) to inform more effective approaches to optimize P removal and enhance the performance of STAs in water treatment and ecosystem restoration efforts.

Distribution of phosphorus and potassium in selected rice cultivated soils and their accumulation in rice grains under farmer-managed field conditions in Sri Lanka

Rice (Oryza sativa L.) is the staple food in Sri Lanka and phosphorus (P) and potassium (K) are major nutrients for the rice plant. However, the variation of P and K contents (mg kg−1) in rice soils and rice grains as affected by agro-climatic zones (ACZs), water source used (i.e., major irrigation, minor irrigation and rain-fed) and cropping systems adopted (i.e., fallow, vegetable, perennials, other field crops) by Sri Lankan farmers are not well elucidated, and are thus investigated in the present study. A total of 200 rice soil and 230 rice grain samples across the country were collected from farmer fields, representing different ACZs, water sources used, and cropping systems adopted using a stratified random sampling approach. The total and available P and K contents in rice soil, and the P and K contents in rice grains were determined. The plant-available P contents in soil were similar among ACZs, water sources, and rice-based cropping systems. Exchangeable K content was higher in rice fields where vegetables were cultivated in the previous season. Grain P and K contents were similar among the water sources used and rice-based cropping systems. Grain P content was the lowest in the Low country Wet zone. Soil available-P and total-P contents (r = 0.29, p &lt; 0.0001), and grain P and K contents were positively correlated (r = 0.51, p &lt; 0.0001). The knowledge generated in the present study is important in P and K nutrient management in rice cultivation in the country.

Leaf nitrogen and phosphorus stoichiometry of the halophytes across China.

Halophytes play a crucial role in the ecological restoration of saline and alkaline land and hold promising benefits to food security in China. Although a variety of aspects of halophytes have been extensively addressed, there is still a lack of overall understanding of the leaf nitrogen (N) and phosphorus (P) stoichiometric characteristics, especially at a national scale. We compiled a national dataset of 311 observations from 113 sampling sites across China to explore the changing trends and influencing factors on leaf N and P concentrations, and N:P ratio of halophytes. The results showed that leaf N concentration decreased significantly with increasing latitude (LAT), which was mainly driven by the mean annual temperature (MAT) and mean annual precipitation (MAP). The leaf P concentration increased remarkably with increasing longitude (LON), which was induced by the variation in soil total P (TP) content. The leaf N:P ratio increased as LAT increased and LON decreased, which was potentially regulated by the MAT, MAP, and soil TP content. The scaling exponents of the N-P relationship differed significantly among halophyte types and were 0.40, 0.87, and 1.39 for euhalophyte, pseudohalophyte, and recretohalophyte, respectively. The leaf N concentration exhibited significant differences among ecosystem types and halophyte types, whereas the leaf P concentration and N:P ratio remained relatively stable. In summary, the leaf N concentration and N-P scaling exponent might be the classification criteria for halophyte types from the perspective of plant nutrient resource allocation. Moreover, this study characterized the spatial distribution and allocation strategy of leaf N and P stoichiometry in halophytes by data integration analysis, providing the basic information for nutrient management in the processes of the future domestication and introduction of halophytes.

Spatial and temporal variations of soil nutrients of cropland in Northeast China from the 1980s to the 2010s.

In recent years, the degradation of cropland soils in Northeast China, such as "thinned, barren, and hardened", has become increasingly serious, with consequences on sustainable development of agriculture. Based on the data from Soil Types of China (1980s) and Soil Series of China (2010s), we examined the change patterns of soil nutrient conditions across different regions and soil types in Northeast China over the past 30 years through the statistical analysis of large samples. The results showed that: 1) from the 1980s to the 2010s, soil nutrient indicators in Northeast China changed to different degrees. Soil pH decreased by 0.03. Soil organic matter (SOM) content decreasd most prominently, by 8.99 g·kg-1 or 23.6%. Soil total N (TN), total P (TP) and total K (TK) contents showed increasing trends, with increases of 17.1%, 46.8%, and 4.9%, respectively. 2) Changes in soil nutrient indicators differed across different provinces and cities. Soil acidification in Liaoning was the most obvious, with pH decreasing by 0.32. SOM content in Liaoning decreased most significantly, by 31.0%. Soil TN, TP, and TK contents in Liaoning increased most significantly by 73.8%, 248.1% and 44.0%, respectively. 3) The changes of soil nutrients varied greatly among soil types, with brown soil and kastanozems showing the greatest decrease in pH. The SOM content of all soil types showed a decreasing trend, with 35.4%, 33.8% and 26.0% reduction in brown soil, dark brown forest soil and chernozem respectively. The greatest increase in TN, TP and TK contents were observed in brown soil by 89.1%, 232.8%, and 48.5%, respectively. In summary, declining organic matter content and soil acidification were the core problems of soil degradation in Northeast China from the 1980s to the 2010s. Reasonable tillage methods and targeted conservation strategies are critically needed to ensure the sustai-nable development of agriculture in Northeast China.

Effects of Organic Materials on Phosphorus Fractions and phoD-harboring Bacterial Community in Karst Soil

Efficient utilization of organic materials based on the rich resources in the karst region can promote soil fertility. Microorganisms have a crucial influence on soil phosphorus availability. phoD is considered to be the encoding phosphatase gene that can reflect the hydrolysis of organophosphorus compounds for the soil bacterial community. Molecular analysis of the phoD-harboring bacterial gene provides insight into promoting soil phosphorus availability under different fertilization managements. However, the effects of organic materials on soil phosphorus fractions associated with phoD-harboring bacterial communities are poorly understood. This study comprehensively investigated the effects of organic materials on soil phosphorus availability and explored environmental drivers of phoD-harboring bacteria in the Karst region. Here, six treatments were designed in the field as follows:non-fertilized control (CK), inorganic fertilization (NPK), inorganic fertilization combined with straw (NPKS), inorganic fertilization combined with manure (NPKM), inorganic fertilization combined with sludge (NPKL), and inorganic fertilization combined with sugarcane ash (NPKA). The phoD-harboring bacterial community in Karst region soil was analyzed using high-throughput sequencing. The results showed that the content of total P (TP), Olsen-P, and Ca2-P increased with the years after organic material application, whereas the content of CaCl2-P first decreased and then increased. Compared to that under the CK treatment, organic material application, especially NPKL treatment, significantly increased soil total nitrogen (TN), TP, Olsen-P, CaCl2-P, and Ca2-P contents, followed by those in the NPKA and NPKM treatments. Correlation analysis showed that the contents of CaCl2-P, Ca2-P, and Olsen-P were significantly positively correlated with soil exchangeable calcium (Ca-ex) content. Redundancy analysis (RDA) showed that TN, Ca-ex, soil organic carbon (SOC), and total potassium (TK) contents were the key factors affecting soil P fractions. Using high-throughput sequencing, we found that only NPKS increased the richness of phoD-harboring bacteria compared to that under the control treatment. No significant difference was observed in the phoD-harboring bacterial community among all treatments. The RDA model selected the Ca-ex, TK, Olsen-P, pH, and SOC as the key environmental predictors for the phoD-harboring bacterial community. In summary, soil phosphorus availability can be improved through the input of organic materials and inorganic fertilizer combined with manure, sludge, and ash. These additions were suitable for nutrient management and sustainable development in farmland soil in the Karst region of Guangxi.

Soil nutrient contents and stoichiometry within aggregate size classes varied with tea plantation age and soil depth in southern Guangxi in China

Abstract. Soil ecological stoichiometry offers a tool to explore the distribution, cycling, limitation, and balance of chemical elements in tea plantation ecosystems. This study aimed to explore how soil organic C (OC) and nutrient contents (total N (TN), total P (TP), Ca2+, Mg2+, Fe2+, and Mn2+) as well as their stoichiometric ratios (C/N, C/P, N/P, Ca/Mg, and Fe/Mn) varied with tea plantation age (8, 17, 25, and 43 years) and soil depth (0–10, 10–20, 20–40, and 40–60 cm) within aggregates in southern Guangxi in China. Our results showed that tea plantation age and soil depth significantly affected soil nutrient stoichiometry in different sizes of aggregates. Among different ages of tea plantations, soil OC, TN, and TP contents as well as C/N, C/P, and N/P ratios significantly decreased as the soil depth increased. In addition, soil Ca2+ and Mg2+ contents were significantly lower in the surface soil layer than the deeper soil layer, whereas soil Fe2+ and Mn2+ contents showed opposite trends, and no significant differences were detected in Ca/Mg and Fe/Mn ratios among different soil depths. At the 0–40 cm soil depth, continuous planting of tea corresponded to increases in soil OC, TN, Fe2+, and Mn2+ contents, whereas soil Ca2+ and Mg2+ contents significantly decreased over time. During the process of tea growth, the losses of soil Ca2+ and Mg2+, especially Ca2+ (as indicated by the decrease in the soil Ca/Mg ratio), led to soil acidification, which reduced Fe2+ absorption and enhanced Mn2+ uptake by tea plants (as indicated by the increase in the soil Fe/Mn ratio). In general, tea plantation age affected the variations of soil nutrient contents and stoichiometry, and such effects were more obvious at the 0–40 cm soil depth, in contrast to the 40–60 cm soil depth.

Variations in Soil C, N, P Stocks and Stoichiometry With Soil Depth and Forest Types in Qilian Mountains of Northwest China

Forests ecosystem plays a significant role in supplying multiple services given the unique properties of forest soils, in which the elements of C, N, and P are essential to support soil fertility and site productivity. However, soil properties at different soil depths between plantation forests (PF) and natural forests (NF) have not been well quantified. Therefore, the current study was carried out in the Qilian Mountains of northwest China to determine the difference between PF and NF in the soil properties, both physical (e.g., bulk density, BD) and chemical (e.g., pH value, the contents, stocks, and stoichiometry of soil organic carbon (SOC), total N (TN), and total P (TP)). Research analyzed soil samples at different depths (0–20, 20–40, 40–60, 60–80, and 80–100 cm). The results showed that the soils’ pH values and BD were significantly higher (p≤ 0.05) in PF than in NF and increased with soil depth. The contents of SOC, TN, and TP decreased considerably with soil depth and then stabilized at the soil depth of 80–100 cm. The NF showed significantly higher (p≤ 0.05) SOC, TN, and TP contents than PF, confirming that the soil quality of PF had not fully recovered yet. The stocks of SOC and TN quickly decreased with soil depth up to 40–60 cm and stabilized gradually. Additionally, the soil stoichiometry of C:P and N:P decreased significantly with rising soil depth, while the C:N ratio remained unchanged. The N:P and C:P ratios were lower in PF than in NF, while the C:N ratio was higher in PF than in NF. In conclusion, the results show that the soils of NF present significantly higher stocks of SOC and TN but lower (or nearly equal) TP stocks than PF (under the same age group and tree species composition). These results imply that maintaining NF and avoiding their replacement by PF can help keep higher soil quality and related ecosystem services.

Soil Phosphorus Sources and Their Relative Water Solubility and Extractability

ABSTRACT Soil testing is a tool used to predict crop response to residual soil phosphorus (P). It is commonly perceived that high soil test P indicates high potential for off-site movement and impact on surface water quality. However, P source potentially confounds the relation between soil test P and soil P solubility. This study evaluated how soil test P (Mehlich-1 and Mehlich-3) and total P (TP) related to water-soluble P (WSP) for manure-(n = 120) and fertilizer-amended (n = 120) soils, and soils forming in phosphate-rich parent material (phosphatic soils; n = 60). Results document marked differences in slopes of WSP as a function of soil test P and TP for the three P sources. Manure-amended soils showed the highest regression coefficients (R 2 = 0.89, 0.89 and 0.92) and slopes for WSP but phosphatic soils, in contrast, showed no tendency for increased WSP with increasing soil test P or TP despite having the highest range of TP content. Fertilizer-amended soils had lowest values for all P measures. Manure-applied P accumulated to much higher levels in these sandy soils than P applied as inorganic P suggesting the latter is either quickly recovered by crops or lost. Phosphate minerals in naturally phosphatic soils do not likely constitute the same extractable P pool as for agriculturally amended soils. Hence, soil test extractions may not be well-calibrated for phosphatic soils. Standard soil test P values may not be a reliable indicator of high P leaching loss potential for naturally phosphatic soils, to the extent that WSP is related to leaching risk.

Expression of PHT1 family transporter genes contributes for low phosphate stress tolerance in foxtail millet (Setaria italica) genotypes.

This is a first comprehensive study to analyze the 12 PHT1 family phosphate transporter genes in 20 foxtail millet genotypes for the improvement of millets and other crops for phosphate use efficiency. Phosphorus (P), absorbed from soil solutions as inorganic phosphate (Pi), is a limiting nutrient for plant growth and yield. Twenty genotypes of foxtail millet (Setaria italica) with contrasting degree of growth and Pi uptake responses under low Pi (LP) and high Pi (HP) supply were chosen based on a previous study. To gain molecular insights, expression dynamics of 12 PHosphate Transporter 1 (PHT1) family (SiPHT1;1 to 1;12) genes were analyzed in these 20 genotypes and compared with their Pi and total P (TP) contents. SiPHT1;1, 1;2, 1;3 and 1;8 genes were expressed in shoot tissues of three (ISe 1209, ISe 1305 and Co-6) of the LP best performing genotypes (LPBG); however, they were expressed in only one of the LP worst performing genotype (LPWG) (ISe 748). More importantly, this is correlating with higher shoot Pi and TP contents of the LPBG compared to LPWG. Apart from this condition, expression of SiPHT1 genes and their Pi and TP contents do not correlate directly for many genotypes in other conditions; genotypes with low Pi and TP contents induced more SiPHT1 genes and vice versa. Promoter analysis revealed that genotype ISe 1888 with a high level of SiPHT1;8 expression possesses two additional root box motifs compared to other genotypes. The PHT1 family genes seem to play a key role for LP stress tolerance in foxtail millet and further studies will help to improve the P-use efficiency in foxtail millet and other cereals.

The impact of different morphological and biochemical root traits on phosphorus acquisition and seed yield of Brassica napus

Abstract Oilseed rape (Brassica napus L.) is an important crop in China. Although its yields are restricted by phosphorus (P) supply, the response of its root system to P supply has not been explored systematically. This study aimed to investigate the contribution of root morphological and biochemical traits to P acquisition from soils with deficient P (30 kg P2O5 ha−1) and sufficient P (90 kg P2O5 ha−1) supplies in the field at the leaf development, stem elongation, flowering, pod development and ripening stages. The total root length and root surface area in the surface soil (0−10 cm soil layer) were both reduced significantly by decreasing P supply. However, a larger root/shoot ratio and root length ratio were observed in plants with the deficient P supply at the flowering stage. Roots of plants with a deficient P supply also secreted more acid phosphatase and organic acid into the rhizosphere from stem elongation to pod development than plants with a sufficient P supply. Seed yield (SY), shoot dry weight (SDW) and total P content (TPC) were strongly correlated with root morphological traits at the leaf development and flowering stages, especially with the coarse root length (CRL) and root surface area in the surface soil. However, there were no correlations between SDW or TPC and root biochemical traits (rhizosphere pH, acid phosphatase activity and organic acid content). It is hypothesized that greater CRL in the surface soil (0−10 cm soil layer) at the leaf development and flowering stages, served as a scaffold for fine roots, enhancing soil exploration and P acquisition, and, thereby, increasing seed yield.

Nitrogen and phosphorus losses from paddy fields and the yield of rice with different water and nitrogen management practices

The assessment and control of losses of nitrogen (N) and phosphorus (P) from paddy fields is critical to improve the quality of water and atmosphere on earth. A field experiment was conducted to investigate the effect of three N managements (local common N fertilization practice, urea mixed with controlled-release N fertilizer, and optimized and reduced N fertilizer, designated CN, U + CRF and ON, respectively) on N and P losses through runoff and leaching from a paddy field, and yield of rice under shallow-irrigation and deep-sluice (SIDS) and continuous flooding irrigation (FI) in the Jianhan Plain of China in 2016. The results showed that, compared with FI, SIDS significantly reduced the frequency of irrigation and amount of irrigation water, resulting in an increase of 16.2% in rainfall use efficiency, and therefore, a reduction in the amount of surface runoff and water that had leached. This was responsible for the decreased total N (TN) and total P (TP) losses through runoff leaching under SIDS. The U + CRF and ON treatments resulted in a significant reduction in losses of TN through runoff and leaching and the loss of TP through leaching compared to CN. SIDS resulted in comparable or greater soil TN and TP contents in the 0–40 cm soil depths after rice harvest; N and P accumulation at the jointing, filling and maturity stages; and yield of grain compared to FI. Moreover, the U + CRF and ON improved or maintained accumulation of N and P and yield of rice compared to CN. Compared with FI coupled with CN, SIDS coupled with the U + CRF or ON treatments significantly reduced losses of N and P from paddy fields and enhanced or maintained the accumulation of N and P and yield of rice grains. In conclusion, SIDS coupled with the new N management could be an effective approach to reduce losses of N and P from paddy fields and would be a positive improvement for high yield of middle-season rice grains in the Jianhan Plain of central China and other regions with similar environments.

Effects of different management approaches on the stoichiometric characteristics of soil C, N, and P in a mature Chinese fir plantation

Carbon (C), nitrogen (N), and phosphorus (P) are commonly used to evaluate soil quality. However, still little is known about the effects of human activities on soil C, N, and P. In this study, we compared the stoichiometric characters of soil C, N, and P in a mature Chinese fir (C. lanceolata) plantation under four forest management approaches: uncut as a control (NC), clear-cutting (CC), controlled burning after clear-cutting (CCB) and conversion into a tea garden (TG). We measured the total C (TC), total N (TN), and total P (TP) contents and evaluated the ratios of C:N, C:P, N:P, and C:N:P in each treatment. The results showed that: (1) the contents of TC and TN in all management approaches decreased with increasing soil depth, while the TP content in NC, CC, and CCB decreased at first, then increased. More importantly, there was no significant difference in TP content under the four management approaches. (2) The ratios of C:N, C:P, N:P, and C:N:P decreased with increasing soil depth. Interestingly, the ratio of C:N was lower than that of C:P in every management approach. (3) Despite the different management approaches (NC, CC, CCB, and TG), the ratios of soil C:N:P were relatively stable, which were 24:4:1, 26:4:1, 21:3:1, and 21:3:1, respectively. CCB showed the greatest negative effect on soil TC, TN, and TP contents, suggesting it might be beneficial to avoid this approach for Chinese fir management.

Enhanced soil aggregate stability limits colloidal phosphorus loss potentials in agricultural systems

BackgroundColloid-facilitated phosphorus (P) transport is recognized as an important pathway for the loss of soil P in agricultural systems; however, information regarding soil aggregate-associated colloidal P (Pcoll) is lacking. To elucidate the effects of aggregate size on the potential loss of Pcoll in agricultural systems, soils (0–20 cm depth) from six land-use types were sampled in the Zhejiang Province in the Yangtze River Delta region, China. The aggregate size fractions (2–8 mm, 0.26–2 mm, 0.053–0.26 mm and < 0.053 mm) were separated using the wet sieving method. Colloidal P and other soil parameters in aggregates were analyzed.ResultsOur study demonstrated that 0.26–2 mm small macroaggregates had the highest total P (TP) content. In acidic soils, the highest Pcoll content was observed in the 0.26- to 2-mm-sized aggregates, while the lowest was reported in the < 0.053 mm (silt + clay)-sized particles, the opposite of that revealed in alkaline and neutral soils. Paddy soils contained less Pcoll than other land-use types. The proportion of Pcoll in total dissolved P (TDP) was dominated by < 0.053 mm (silt + clay)-sized particles. Aggregate size strongly influenced the loss potential of Pcoll in paddy soils, where Pcoll contributed up to 83% TDP in the silt + clay-sized particles. The Pcoll content was positively correlated with TP, Al, Fe, and the mean weight diameter. Aggregate-associated total carbon (TC), total nitrogen (TN), C/P, and C/N had significant negative effects on the contribution of Pcoll to potential soil P loss. The Pcoll content of the aggregates was controlled by the aggregate-associated TP and Al content, as well as the soil pH value. The potential loss of Pcoll from aggregates was controlled by its organic matter content.ConclusionWe concluded that management practices that increase soil aggregate stability or its organic carbon content will limit Pcoll loss in agricultural systems.

The total P estimation with hyper-spectrum – A novel insight into different P fractions

Phosphorus (P) is one of the main characterization parameters of soil fertility and an important element affecting vegetation growth. This paper used the multivariate stepwise regression to estimate the soil P concentration through multiple mathematical transformation of the original spectrum, evaluate the accuracy of different models, and determine the optimal modeling method. The total P (TP) is classified as loosely adsorbed P (Ad-P), P bound by iron oxides or hydroxides (Fe-P), aluminum-bound P (Al-P), calcium-bound P (Ca-P) and residual P (Re-P). Then the relationship between various P fractions and soil properties and their spectral characteristics were analyzed. The effects of different P fractions on total P (TP) estimation were discussed from the aspects of selected bands, corresponding forms and spectral transformation forms, the direct and indirect estimation models are constructed respectively, which provided a new idea for soil spectrum estimation of soil properties. The results show that (1) Al-P is the main component of TP, and its spectral characteristics are not obvious, and the correlation coefficient between Al-P and TP is 0.437, which is the main reason for the stability of TP estimation model. (2) Soil organic matter and Ca-P have the greatest influence on TP estimation. When the band is less than 1200 nm, soil organic matter concentration is the main factor affecting TP estimation. When the wavelength is greater than 1200 nm, Ca-P is the main factor affecting TP estimation. (3) An indirect estimation model of TP was developed by using Ca-P, the R2 of the calibration reached 0.78, and the R2 of the validation reached 0.66, the model is stable and can be used to estimate TP content. It is proved that it is a feasible method to estimate the TP content through the spectral characteristics of P fractions, the relationship between organic matter and TP is not the only key reason for the successful estimation of TP.

Distribution of phosphorus fractions with different plant availability in German forest soils and their relationship with common soil properties and foliar P contents

Abstract. Repeated, grid-based forest soil inventories such as the National Forest Soil Inventory of Germany (NFSI) aim, among other things, at detecting changes in soil properties and plant nutrition. In these types of inventories, the only information on soil phosphorus (P) is commonly the total P content. However, total P content in mineral soils of forests is usually not a meaningful variable with respect to predicting the availability of P to trees. Here we tested a modified sequential P extraction according to Hedley (1982) to determine the distribution of different plant-available P fractions in soil samples (at depths of 0–5 and 10–30 cm) from 146 NFSI sites, encompassing a wide variety of soil conditions. In addition, we analyzed relationships between these P fractions and common soil properties such as pH, texture, and soil organic carbon content (SOC). The total P content among our samples ranged from approximately 60 to 2800 mg kg−1. The labile, moderately labile, and stable P fractions contributed to 27 %, 51 %, and 22 % of the total P content, respectively, at a depth of 0–5 cm. At a depth of 10–30 cm, the labile P fractions decreased to 15 %, whereas the stable P fractions increased to 30 %. These changes with depth were accompanied by a decrease in the organic P fractions. High P contents were related to high pH values. While the labile Hedley P pool increased with decreasing pH in absolute and relative terms, the stable Hedley P pool decreased in absolute and relative terms. Increasing SOC in soils led to significant increases in all Hedley P pools and in total P. In sandy soils, the P content across all fractions was lower than in other soil texture types. Multiple linear regression models indicated that Hedley P pools and P fractions were moderately well related to soil properties (with r2 values that were mostly above 0.5), and that the sand content of soils had the strongest influence. Foliar P contents in Pinus sylvestris were reasonably well explained by the labile and moderately labile P pool (r2 = 0.67) but not so for Picea abies and Fagus sylvatica. Foliar P contents in all three species could not be related to specific Hedley P pools. Our study indicates that soil properties such as pH, SOC content, and soil texture may be used to predict certain soil Hedley P pools with different plant availability on the basis of large soil inventories. However, the foliar P contents of tree species cannot be sufficiently well predicted by the soil variables considered here.

Dynamics of soil physical and chemical properties within horizontal ridges-organic fertilizer applied potato land

Although the horizontal (contour) ridge has been shown to be significantly effective in reducing erosion within potato land in our previous study, it tends to enhance waterlogged in the soil by which the productivity of crop may be decreased. Beside the availability of organic materials, the dimension of ridge may also affect the waterlogged. However, their impact on the soil properties have been yet less paid attention. This study was aimed to identify the effect of horizontal ridges dimensions on soil physical and chemical properties over organic fertilizer applied potato land. Totally 9 potato plots of 3×3 m2 were prepared in Serang village, Purbalingga with three different dimensions and replications of the horizontal ridges: 30× 30×30 cm3 (HR30), 30×40×30 cm3 (HR40), and 30×50×30 cm3 (HR50). Petroganik (C-org: 12.5%, C/N ratio: 10-25) fertilizer of 20 ton ha-1 was applied into these plots. Soil samples were collected from each plot at 0, 8, 35, 71, and 91 days after planting using 100-cc ring samplers. The physical (volumetric water content, dry bulk density, permeability) and chemical (total-N, total-P) properties of soil were then analyzed in laboratorium using gravimetric and Kjeldahl-Colorimetric method, respectively. The results showed that the soil volumetric water content and dry bulk density increased with increasing the ridges dimensions, of which the highest values of 0.450 cm3cm-3 and 0.730 gcm-3 each were found in HR50. Conversely, the soil permeability decreased with increasing the ridges dimensions, of which the highest value of0.027 cms-1 was encountered in HR30. The soil total-N and total-P contents were slightly fluctuated, of which the highest values of 4.111 and 2.213 tonha-1 each were seen in HR40. Thus, the horizontal ridge with 40 cm-width might be the most suitable for the organic potato cultivation.

Use of plant growth promoting Rhizobacteria (PGPR) and mycorrhizae to improve the growth and nutrient utilization of common bean in a soil infected with white rot fungi

Extensive use of fertilizers and pesticides led to dangerous ecological effects and therefore the biological approaches have been widely recommended to prevent further deterioration for the environment. The current study was conducted to explore the potentiality of using single or combined inoculations by mycorrhizae, Bacillus subtilis and Pseudomonas fluorescence for controlling the infection of common bean plants with Sclerotium rolfsii on one hand and as bio-fertilizers for improving plants nutritional status on the other hand. The soil of study was mildly infected with S. rolfsii and contained high total-P content. Thus, minimal P inputs were added to the inoculated soil in the form of rock phosphate. Activities of plant defense enzymes i.e. chitinase, peroxidase and polyphenol oxidase were determined under the greenhouse conditions and the results obtained herein indicated that activities of such enzymes increased significantly owing to bio-agent inoculations. In this concern, combined treatments resulted in further significant increases over the single ones. A field study was then conducted for two successive years and the results reveal that single inoculations increased straw and green pod yields as well as the uptake of P and Fe by plants as compared with the non-inoculated treatment. Combined inoculants recorded further significant increases in these parameters even when compared with the fungicide treated plants. Generally, straw and pod yields obtained from the second growing season were significantly higher than those attained in the first growing one. Our study confirms the success of the used bio-treatments in minimizing soil pollution through fertilizer and/or pesticide inputs.

Comparison of phosphorus sorption characteristics in the soils of riparian buffer strips with different land use patterns and distances from the shoreline around Lake Chaohu

Purpose The construction of riparian buffer strips has become increasingly important due to the effective phosphorus (P) retention of the strips, thus preventing eutrophication in freshwater ecosystems. The key mechanism is P sorption in soils. To provide some suggestions for increasing the sorption ability of P, the relationships between P sorption behavior and both land use patterns and distance from the shoreline were determined. Materials and methods In April, July, and October 2013, field investigations were carried out along the shoreline of Lake Chaohu. Eleven sections, including 36 sampling sites at different distances from the shoreline, were chosen, and these sections contained different types of riparian buffer strips, such as grassland, farmland, forest, wetland, and forest/grassland. The P species, sorption parameters, and dominant vegetation species were analyzed. Results and discussion The total P (TP) and P sorption maximum (Q(max)) showed no recognizable seasonal variation and were closely correlated with the distance from the shoreline. The further the distance from the shoreline, the higher the TP and Q(max) values, suggesting that soil traits could determine the P sorption extent. However, the Olsen-P content and equilibrium P concentration (EPC0) fluctuated greatly, with the peak occurring in spring and the minimum occurring in summer in the majority of the sampling sites. In addition, positive relationships existed between the TP content and the Q(max) value as well as the Olsen-P content and the EPC0 value. Canonical correlation analysis (CCA) further showed that the Olsen-P content and EPC0 values were closely related to the dominant vegetation species, indicating that land use patterns played a decisive role in regulating the P sorption strength and the level of available P. Conclusions To effectively adsorb P (increase Q(max)) and prevent P leaching (reduce the EPC0), we recommend changing the land use patterns (more constructed wetlands and forests with grass) in riparian buffers.