Phosphorus-Sorption Characteristics and Phosphorus Buffer Coefficients of Some Important Soils in Lao PDR

An estimated 97 percent of the soils in Laos are characterized by low phosphorus (P). This characteristic, together with high acidity, constrains food crop production. The P status, sorption, and associated properties were evaluated for fifteen important agricultural soils from the uplands. Soil pH values ranged from 4.5 to 5.9. Soil organic carbon (C) varied from 7.0 to 22.9 g kg^?1. Soil clay varied from 179 to 709 g kg^?1. The cation exchange capacity (CEC) also varied from 4.30 to 32.1 cmol_c kg^?1. Extractable P levels of thirteen of the fifteen soils were P deficient with medium to very high P sorption, indicating substantial fertilizer P requirements. Dithionite and oxalate aluminum and iron predicted P sorbed at 0.2 mg P L^?1. The extractable P increase per unit added P, P buffer coefficient (PBC), was low, also indicating high P sorption. Field studies are needed to confirm predictions of P requirements.     

天鹅湖潟湖表层沉积物磷的吸附容量及潜在释磷风险

研究了天鹅湖潟湖表层沉积物对磷的吸附容量,分析了沉积物磷吸附指数(PSI)、磷吸附饱和度(DPS)及由这两个指标构成的磷释放风险指数(ERI),预测了不同区域沉积物磷的潜在释放风险。结果表明,沉积物的PSI变化范围为7.44~28.53 mg L/100 gμmol,湖北部和中部沉积物的PSI值较高;DPS与PSI的变化趋势相反,变幅为0.85%~4.99%,表现为湖南部和中部沉积物的DPS高于北部。沉积物的PSI与磷的理论吸附容量(Qmax)呈极显著正相关(P0.01),而DPS与沉积物各理化参数间的相关性较差。有机质(OM)、活性铝(Alox)和粘粒是表层沉积物对磷持留的主要影响因素。此外,天鹅湖潟湖表层沉积物的ERI变化范围为2.93%~44.70%,磷释放诱发富营养化的风险处于中度范围,其中东南部发生富营养化的风险较高     

Effects of equilibrating salt solutions on phosphate sorption by soils

Abstract

Several equilibrating salt solutions have been used in the studies of P sorption by soils and sediments. This study was conducted to evaluate the effects of 10 salt solutions on estimation of P sorption by soils. Results obtained showed that, when the equilibrating solution was made to contain 0.01M with respect to CaCl₂, Ca(NO₃)₂, CaSO₄, MgCl₂, KCl, LiCl, Nacl, or KHCO₃, the amount of P sorbed by soil always exceeded the amount sorbed from the soil‐water system. In comparison with the amount of P sorbed from water, 0.01M NaHCO₃ reduced P sorption by soils. Use of THAM buffer (0.05M pH 7.0) to control the pH increased P sorption by some soils and decreased P sorption by others, relative to that sorbed from the soil‐water system. The results indicated that inclusion of salts in the equilibrating solution for P‐sorption studies should be avoided, especially in studies related to water quality.     

磷在土壤中有效性的衰减

培育试验表明,磷与红壤中有效性的衰减可分为快反应（3小时）阶段和慢反应阶段,前者有效磷以直线关系下降,后者则为一渐减性曲线。快反应阶段磷有效性的衰减量和土壤活性铝含量显著相关,但与活性铁和交换铝相关不显著。用红壤、潮土、板浆白土三种性质不同的土壤进行的生物试验表明,产量也随着土－磷作用时间延长而下降,而且有一个终止时间,中性水稻土在8个月培育后产量即可不再下降,石灰性潮土为16个月,而酸性红壤在28个月以上,影响产量衰减的可能和磷在土壤中的双核化（转化为环状双核结构）和吸收作用有关,它们在程度上和延续时间上不同土壤不同,在水稻土上最弱,延长时间最短,而在红壤上作用最强,延长时间最长,潮土处于两者之间。     

Assessing alternative approaches to predicting soil phosphorus sorption

Twenty‐five pasture soils were sampled from high‐rainfall zones of southeastern Australia to examine relationships between soil properties, and between soil properties and P buffering capacity (PBC) measures. Correlations between PBC values and soil properties were generally poor, with the exception of oxalate‐extractable Al (Al_ox) (r ≥ 0.97). Predictions of PBC were further improved when clay, as well as Al_ox, was included in a linear regression model (r² ≥ 0.98). When Al_ox and oxalate‐extractable Fe were excluded from the modelling exercise, a more complex three‐term linear regression model, including pH_H2O, exchangeable H and cation exchange capacity, adequately fitted both PBC values of the 25 soils examined in this study (r² ≥ 0.76). However, the Al_ox, Al_ox plus clay and the three‐term models gave poor predictions of the PBC values when the models were validated using 28 independent soils. These results emphasize the importance of model validation, because predictive models based on soil properties were not robust when tested across a broader range of soil types. In comparison, direct measures of PBC, such as single‐point P sorption measures, are more practical and robust methods of estimating PBC for Australian soils.     

Prediction of phosphorus requirements of Desmodium intortum cv. greenleaf using a phosphorus sorption index and extractable phosphorus

Abstract

The rates of applied phosphorus required for 90% maximum yield of Desmodiim intortum cv. Greenleaf were calculated from pot experiments using 24 fertilized and unfertilized soils from the Atherton Tableland, Queensland, Australia.

Phosphorus required was highly correlated (r² = 0.94) with the phosphorus sorbed (P sorbed) by the soils at a supernatant solution P concentration of 0.08 ppm. P sorbed was found to be a function of phosphorus buffer capacity at 0.08 ppm ("PBC") and phosphorus extractable by acid (0.005 M H₂S0₄) or bicarbonate (0.5 M NaHCO₃). PBC was highly correlated (r² = O.84) with a phosphorus sorption index ("PSI") derived from one addition of 500 μg P g^‐1 soil.

Combining PSI with acid or bicarbonate extractable P in a multiple regression equation allowed the estimation of phosphorus required with multiple correlation coefficients of R² = 0.80 and R² = 0.83 respectively.     

Characteristics of P accumulation and distribution at the maturity stage of Brassica Napus varieties with different phosphorus use efficiency for grain production

Phosphorus (P) is one of nutrients essential for plant growth. The differences in P content, accumulation, and distribution among 98 rapeseed (Brassica napus) varieties with different P use efficiency for grain production (PUEg) were studied. The results showed that there were highly significant differences in P contents of the whole plant and various organs among different rapeseed varieties. Furthermore, PUEg had significantly negative correlations with P accumulations in whole plant, stems, shells, and seeds. The correlation analysis showed that the correlation coefficient of PUEg and P distribution ratio in stems was smaller, and it was significantly negatively correlated in shells, while it showed highly positive correlations in seeds. It indicated that P content in rapeseed plant stems and shells appeared to be transported into seeds to increase P distribution in seedpods at the late maturity stage, which could help improve PUEg.     

Enzymatic hydrolysis of organic phosphorus in extracts and resuspensions of swine manure and cattle manure

Animal manure can be a valuable resource of P for plant growth. Organic phosphates (P_o) are considered bioavailable if they can be hydrolyzed to inorganic P (P_i). Therefore, investigation of the susceptibility of manure P_o to hydrolysis may increase our understanding of manure P_o bioavailability. In this study, we demonstrate that three orthophosphate-releasing enzymes, acid phosphatase from wheat germ, alkaline phosphatase from bovine intestinal mucosa, and fungal phytase from Aspergillus ficcum, were able to hydrolyze certain amounts of P_o in animal manure. A scheme of sequential enzymatic release of P_o in manure was developed and then used to investigate changes in swine and cattle manure P distribution after storage at –20°C, 4°C or 22°C for about a year. Assuming that the P distribution in manure maintained at –20°C remained unchanged (i.e., similar to fresh manure), bioavailable P (P_i and enzyme-hydrolysable P_o) in swine manure remained relatively constant [72.8–76.3% of total P (P_t)]. Soluble but enzymatically unhydrolysable P_o (P_ue) increased from 7.2% to 32.1% of P_t during storage at 4°C. In cattle manure, bioavailable P decreased from 71.6% to 62.9% of P_t, and P_ue increased from 21.7% to 37.2% of P_t during storage at 22°C. These data indicated that the major change during the storage of animal manure for a year was the increase in P_ue, so manure P solubility may increase with storage, but the increase would not produce more bioavailable P in the manure. The effects of storage on the bioavailability of manure P should be further investigated to develop an efficient manure-P management strategy.Trade or manufacturers' names mentioned in the paper are for information only and do not constitute endorsement, recommendation, or exclusion by the USDA-ARS     

有机磷在调节土壤磷素保持与释放过程中的作用

以巢湖沿岸土壤和沉积物为对象,分析了速效磷、藻类可利用性磷、有机磷含量和碱性磷酸酶活性的空间变化格局,并测定了磷吸附参数.结果表明,土壤有机磷含量差异显著,以草地最高,而速效磷和藻类可利用性磷含量无明显差异;酶活性及速效磷含量与有机磷含量呈显著正相关,土壤对正磷酸根的吸附量与土壤中有机磷含量呈正相关;湖泊沉积物中有机磷含量与周边土壤中有机磷含量显著正相关.因此,土壤有机磷及其酶促水解过程是调节沉积物作为磷源或磷汇功能的关键因素之一.     

长期施肥对酸性土壤磷形态及有效性的影响

为明确长期施肥对集约化果园土壤磷形态、分布特征及其有效性的影响,本研究对琯溪蜜柚主产区29个果园的土壤进行调查研究,采用张守敬和Jackson的酸性土壤无机磷分级方法,研究蜜柚果园土壤磷素累积对土壤磷形态及有效性的影响。结果表明：在集约化蜜柚果园中,土壤磷素累积丰富,随树龄增加土壤速效磷含量上升显著,且土壤磷形态在不同土层存在显著性差异;当全磷含量≤0.5 g/kg时,土壤磷形态主要以有机磷、铁磷为主,随着全磷含量的上升,铝磷含量、占比均显著上升;多元线性回归和逐步回归分析结果表明本试验中铝磷与速效磷相关性最好。果园土壤已经形成一个巨大的磷库,且有效性较高,可适当减少磷肥投入,降低土壤磷含量,减少经济成本,提高生态效益。     

长期定位施肥对土壤磷素吸持特性与淋失突变点影响的研究

通过对黄土旱塬地区长期(26a)定位施肥条件下的不同施肥处理的土壤磷素及其吸持参数的测定,以及通过室内模拟试验对土壤磷素淋失突变点的测定,研究了土壤磷素吸持参数、土壤磷素淋失突变点和部分土壤性质之间的关系。结果表明,经过26年的长期施肥,M75P60和M75N120P60处理的Olsen-P含量比CK处理的提高了10.7和9.8倍,全磷(T-P)含量比CK处理的提高了60.4%和57.7%。长期磷肥和有机肥投入可以减低土壤磷素的最大吸附量(Qm),而提高土壤磷素的吸附饱和度(DPSS),M75N120P60处理的Qm比CK的减低了49.92%,而DPSS比CK的提高了21.5倍。相关分析表明,黄土旱塬土壤的Qm与Olsen-P、T-P和CaCl2-P呈极显著的负相关关系(P<0.01),与土壤有机质呈显著负相关关系(P<0.05)。零净吸附浓度磷(EPC0)与Olsen-P和CaCl2-P呈极显著正相关关系,与T-P和SOM也达到显著正相关,而与pH值的关系不显著,但土壤磷最大缓冲能力(MBC)与pH值的关系达到极显著。DPSS与Olsen-P、T-P、CaCl2-P和SOM呈极显著正相关关系。土壤磷素淋失的Olsen-P突变点值与土壤吸持参数Qm呈极显著正相关,与MBC也达到显著正相关,与DPSS、Olsen-P、T-P和CaCl2-P呈极显著负相关关系。该地区土壤磷素淋失的Olsen-P突变点值与DPSS15%的值极为吻合,即可以用DPSS15%值作为该地土壤磷素淋失的突变点值。     

风沙土不同有机组分对磷的吸附特征影响

采用平衡吸附法研究了风沙土不同有机组分对磷的吸附特征影响,可为有机组分吸附态磷携载量估算提供依据。结果表明：去除有机质后的风沙土对磷的吸附能力大大降低,其碳标化饱和吸附量（Гmo）c和吸附分配系数（ko）c分别只能达到重组的27.76%和8.45%,说明有机质是影响磷在风沙土上吸附特征的重要因素;磷在轻组有机组分上的吸附以分配作用为主（koc=51.02）;风沙土有机组分中的重组有机质对磷的吸附起主导作用（Гmoc=388.35mg.kg-1）,重组有机组分中的紧结态腐殖质（胡敏素）对磷的吸附起关键作用（Гmoc=1007.96mg.kg-1）,影响机制主要为稳、紧结态腐殖质是形成土壤疏松多孔团聚体结构的重要胶结物质。在其所形成的有机矿质复合体中除分配作用吸附外,还存在着孔隙填充方式的磷吸附;考查土壤对磷的吸附能力不但要考虑有机质的含量,更要考虑有机质的存在形态,它也是影响土壤对磷吸附特征的重要因素。以重组为基准,轻组有机组分以及重组有机组分中稳结态腐殖质和紧结态腐殖质携载的吸附态磷分别可按0.69倍以及1.37、2.75倍估算。     

Relationship between Soil Phosphorus Availability and Phosphorus Loss Potential in Runoff and Drainage

Abstract

Elevated soil phosphorus (P) content is common in the central coastal valleys of California, the result of decades of the intensive vegetable production. Undesirably high P concentration in surface water in this region stimulated interest in evaluating techniques to rank the potential for soil P loss to the environment. Phosphorus availability of 25 representative soils from fields in vegetable rotations were evaluated by the following techniques: bicarbonate‐extractable P (P_bc)–calcium chloride, extractable P (P_cc), P extractable by iron‐impregnated paper (P_Fe), P extractable by anion exchange resin (P_ae), and the degree of P saturation (P_sat). A column study was conducted in which these soils were evaluated for soluble P concentration in runoff and leachate from two simulated irrigation events. There were strong correlations among all measures of soil P availability (r=0.66–0.90). Runoff soluble P was most strongly correlated with P_cc, P_ae, and P_bc (r=0.98, 0.93, and 0.91, or 0.98, 0.90, and 0.85 in the first and second irrigation, respectively). The relationship of runoff soluble P to P_bc, P_ae, and P_cc was characterized by a change point; runoff soluble P from soils <50 mg kg^?1 P_bc was minimal, whereas at higher P_bc runoff P reached levels of environmental concern. Leachate soluble P was also correlated with P_cc, P_ae, and P_bc (r=0.84–0.99). Across soils, leachate soluble P averaged 1.4 mg L^?1, compared to 0.11 mg L^?1 for runoff P. We conclude that P_cc, P_ae, and P_bc are useful tests to rank the potential for P loss in irrigation runoff or drainage. Given the relative complexity of the P_ae technique, P_bc and P_cc appear to be the most practical soil tests for this purpose.