The effect of various sources and dose of phosphorus on residual soil test phosphorus in different soils

Catena 105 (2013) 21–28

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The effect of various sources and dose of phosphorus on residual soil test phosphorus in different soils Mustafa N. Shafqat a, b,⁎, Gary M. Pierzynski b a b

Department of Biosciences, COMSATS Institute of Information Technology, Islamabad, Pakistan Department of Agronomy, Kansas State University, Manhattan, KS 66502, USA

a r t i c l e

i n f o

Article history: Received 18 May 2012 Received in revised form 7 January 2013 Accepted 10 January 2013 Keywords: Animal manure phosphorus Soil test phosphorus Residual phosphorus Crop phosphorus uptake

a b s t r a c t Soil test phosphorus (STP) finds its agronomic utility for the recommendation of phosphorus (P) fertilizer to crops and in risk assessment of offsite soil P movement from an environmental perspective. The objective of this research was to understand the influence of P from several P sources applied at 0, 50 and 150 mg P kg−1 on STP in six different soils both before crop P removal (NBP0) and after the first (NBP1) and seventh harvest (NBP7) of corn (Zea mays L.). The P was extracted with Bray1 solution from animal P sources alone as well as from soils amended with P sources. The various net Bray1 (NBP) levels were computed by subtracting Bray1 levels in the control treatments from the P amended treatments. The results suggested that monogastric P sources contained relatively large proportions of Bray1 than ruminants. However, when gross Bray1 levels were expressed as percent of total P, the hog (Sus scrofa) manure (HM) and cattle (Bos taurus) manure 2 (CM2) had identical proportions while sewage sludge (SS) and turkey (Meleagris gallopava) litter (TL) had the least amount of Bray1 extractable P. Both cattle manures and HM resulted in significant higher concentration of NBP0 and NBP1 in most soils among the animal P sources. All P sources in the Eram–Lebo soil and all soils amended with TL at both levels of P application had the least amounts of NBP0 and NBP1. The greatest proportion of total residual P was detected as Bray1 in HM and the least in TL. These findings will be helpful for land managers with high soil test P levels who are under P regulation to help discern how various P sources affect soil Bray 1P. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Animal manures are considered as valuable agricultural by-products and are commonly used in modern agriculture to supply nutrients to the crop plants. Previously, these materials were disposed of through soil application on the basis of crop nitrogen (N) needs which allow for disposal of large quantities of animal manures per unit area (Sims, 1995). However, the major drawback in this approach is that more phosphorus (P) would be added than is removed through the harvested crop. Thus repeated application of animal manures would eventually build up P levels in the soils where it would likely become an environmental threat rather than having any agronomic significance (Shafqat and Pierzynski, 2010; Sims et al., 1998; Toth et al., 2006). Many soils in the continental USA and Europe are high in available P, especially those located in close proximity to animal production facilities. These P rich soils can result in the transport of P in the form of soluble and particulate P to nearby streams and contributes to the deterioration of surface water quality through eutrophication (Pierzynski et al., 2004).

⁎ Corresponding author at: Department of Biosciences, COMSATS Institute of Information Technology, Islamabad, Pakistan. Tel./fax: +92 51 8318471. E-mail address: [email protected] (M.N. Shafqat). 0341-8162/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.catena.2013.01.003

Soil testing for available P was started in the middle part of the last century and used for fertilizer recommendations. It consisted of extracting a soil sample with chemical solutions and the amount of P extracted would represent an index P value against which the likelihood of increased grain yield of a crop to P fertilizer additions would be estimated (Havlin et al., 2004). The important methods of soil P testing included those which used 0.025 M HCl and 0.03 M NH4F solutions (Bray and Kurtz, 1945), 0.5 M NaHCO3 solution adjusted to pH 8.5 (Olsen et al., 1954) and the Mehlich-3 extracting solution which consisted of acetic acid, ammonium nitrate, ammonium fluoride, nitric acid and chelating agent EDTA (Mehlich, 1984). The first method (Bray and Kurtz, 1945) worked well for acid and neutral soils, the Olsen's (Olsen et al., 1954) proved valuable for calcareous soils, and the procedure developed by Mehlich (Mehlich, 1984) was equally useful for soils across a wide range of pH values. All STP methods employ four basic reactions to extract P including anion exchange, acid dissolution, complex formation with solution cations which bind P, and hydrolysis of cations (Sims, 2000). Recently, there is growing interest among the scientific community in the use of STP for environmental monitoring. Many studies have indicated strong relationships between STP and the amount of soluble and particulate P in runoff (Andraski and Bundy, 2003; Shroeder et al., 2004; Torbert, et al., 2002). Moreover, STP was also constituted an important component of P site index procedure used by many States to provide risk assessment

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M.N. Shafqat, G.M. Pierzynski / Catena 105 (2013) 21–28

for the movement of P from an agricultural field to nearby surface water. Other parameters of the P index include the identity of the P sources, rate of application, geographical position, rainfall amount, and type of soil (Lemunyon and Gilbert, 1993). The amount and forms of P in animal manure are influenced by the digestive system, age of the animal, feed additives, and waste processing methods (Barnett, 1994; Dou et al., 2002; Maguire et al., 2003; Poulsen, 2000). The proper growth of the monogastric animals is heavily dependent on supplemental P as they lack phytase in their digestive systems which hydrolyzes the grain phytate P. Therefore, digestion and absorption efficiency is low and a considerable proportion of supplement P mixed with feed is excreted in the manure (Wodzinski and Ulla, 1996). Wienhold and Miller (2004) reported that manure generated by swine fed on low phytate corn grain had lower total P (20 g kg−1) and a higher N to P ratio (4.5) compared to those fed on traditional corn which had higher total P (34 g kg−1) and a lower N to P ratio (3.3). Moreover, the water extractable fraction was less in manure from swine fed on low phytate corn than the traditional corn grains. Similarly, dairy manure treated with salts of Ca, Al, and Fe resulted in increases in Bray1 in the order of Ca treated>Al treated ≥untreated> Fe treated> control, suggesting greater efficiency in reducing the solubility of P by the salts of Al and Fe than Ca (Kalbasi, and Karthikeyan, 2004). Moreover, poultry manure treated with water treatment residual rich in Al, alum (Al2(SO4)3.14H2O), and ferrous sulfates caused reductions in water soluble P factions compared to the untreated poultry manure. Findings from another study suggested that treatment of poultry manure with Al and Fe sulfates caused a significant reduction in both dissolved and total P (Hunger et al., 2004; Seiter et al., 2008; Shreve et al., 1995). Similarly, the treatment of raw sewage with salts of Al, Fe and Ca resulted in lower solubility of P (Hinedi et al., 1989; Maguire et al., 2001). Despite variations in the P content, nature and solubility of P in the animal manure, current manure management guidelines hardly differentiate between the manures, and assume that P in all manures would behave similarly. Therefore, in this study we would monitor the nature of and amount of Bray1 extractable P in different manures alone and as influenced by different P application levels in many different soils both before and after crop P removal. Specifically, we will test the following hypotheses: A) there will be no difference in Bray1 concentrations in different animal P sources, B) the net increase in Bray 1 would be similar in soils amended with manures from monogastric, ruminants and with P fertilizers prior to crop P removal C) the level of P application from different P sources would likely result in proportional increase in Bray1 concentrations across all soils, and D) the net Bray1 levels after harvest one and at the end of study (harvest seven) would be similar for all P sources.

kg −1 soil and allowed to stand for 24 h. An unamended (control) from each soil was also prepared in a like manner. Therefore, there were total of 78 treatments (6 soils* 6 P sources * two P levels + 6 controls) which were arranged in randomized complete block design with three replications. Each pot was sown with 10 seeds of Pioneer corn hybrid 4662 and thinned to 6 plants per pot 10 days after germination. All treatments were harvested 35 days from the date of sowing and a total of seven harvests were achieved during the course of this study. Corn dry weight was recorded after each harvest. Total P uptake was calculated for each treatment and each harvest by multiplying tissue P concentration with plant biomass and was subsequently pooled for all harvests. The complete description of the experiment is available in Shafqat and Pierzynski (2011) and the data on total P uptake in the same study was utilized (Table S1 and data set S1 in the supporting information [Shafqat and Pierzynski, 2011]) for the determination of residual P after harvest 7 and 1, respectively. Briefly, total P uptake from the control treatments in each soil were subtracted from the P amended treatments which were subsequently subtracted from the P application dose for the determination of residual P in each treatment. Soil samples were collected both before cropping and after harvests 1 and 7 for the determination of Bray 1 concentrations (Bray and Kurtz, 1945). The Bray 1 concentrations were also determined from animal manure samples in a like manner. Prior to crop P removal at time zero (T0), the Bray 1 concentrations were determined from soils amended with different P sources and total increase was referred as total Bray 1 concentrations (TBP) (Table S1 supporting information). Net Bray 1 concentrations at time zero (T0) and after harvests 1 and 7 were determined by subtracting the Bray 1 concentrations of the control treatments from the P amended treatments and referred to as NBP0, NBP1, and NBP7, respectively. Phosphorus concentrations in the soil extracts were determined by the procedure of Murphy and Riley (1962). 2.3. Statistical analysis The General Linear Model (Proc GLM) of statistical analysis system (SAS, 2009) was utilized for the testing of various hypotheses using analysis of variance. In case of significant interaction effect the influence of each factor at the levels of other factors were compared while in the absence of interactions, only main effects of the each treatment were compared by utilizing least significant difference (LSD) procedure at alpha value of 0.05. 3. Results and discussion 3.1. Bray1 concentrations in different P sources

2. Material and methods 2.1. Collection of soils and animal P sources Six soils used in the present study were collected from different parts of the state of Kansas, USA. Five animal/organic P (Po) sources were utilized and consisted of two types of stock piled cattle manures, turkey litter, solid hog manure and biosolids. Triple super phosphate (TSP) was included as an inorganic P source for comparative purposes. All soils and animal P sources were air dried, ground to pass b2 mm sieve and stored at room temperature prior to their use in the greenhouse study. Complete descriptions of soils and P source properties are available elsewhere (Shafqat and Pierzynski, 2011). 2.2. Greenhouse study Two kg of each of the 6 soils was amended with 50 and 150 mg P kg −1 from each of the P sources and placed into a plastic pot lined with a plastic bag. These pots were later brought to 200 ml water

Bray 1 concentrations ranged from 2050 to 9300 mg P kg −1 in CM2 and HM, respectively (Table 1). Overall, both cattle manures had lower concentrations of Bray 1 compared to the other P sources. In fact, the Bray1 concentrations in the HM and SS were four to five times higher compared to the levels in CM2 and were nearly double when compared to levels in CM1. The TL had Bray1 levels which were twice as much as in CM2 but the difference was relatively small when compared to CM1. The difference in gross Bray1 levels in both cattle manures (4320 and 2050 mg P kg−1 in CM1 and CM2, respectively) was attributed to the total P levels which were twice as high as in CM1 (8.8 g kg−1) compared to CM2 (3.8 g kg−1). Interestingly, trends opposite both cattle manures were seen in other P sources. The total P content was 17, 21, and 27 g P kg−1 for the HM, TL and SS respectively, but HM had a Bray1 concentration of 9300 mg P kg−1 which was higher than the 5375 and 7910 mg P kg −1 found in TL and SS, respectively. These variations in Bray1 levels could partly be attributed to the amount of supplemental P in the animal diet, the nature of digestion system of the animals, and treatment processes during the waste processing. Cattle

M.N. Shafqat, G.M. Pierzynski / Catena 105 (2013) 21–28 Table 1 Total phosphorus and Bray1 concentrations of different animal P sources used in the study. P sources

CM1 CM2 TL HM SS

Total P

Bray-1

a Expected increase in Bray-1 (mg P kg−1)

g kg−1

(mg P kg−1 P source)

50 mg total P kg−1

150 mg total P kg−1

8.8 3.8 21.0 17.0 27.0

4320 (b49.1%) 2050 (54.0%) 5375 (25.4%) 9300 (54.7%) 7910 (29.3%)

25 27 13 27 15

75 81 39 81 45

CM1 = cattle manure1, CM2 = cattle manure 2, TL = turkey litter, HM = hog manure, SS = sewage sludge a Expected increase in Bray 1P concentrations were measured by multiplying percent Bray 1P levels in each P source with given rate of total P applications. b Bray-1 levels expressed as percent of total P in respective P source.

are ruminants while the TL, HM and SS-P sources would reflect monogastric digestive processes. The hydrolysis of Po contained in the forages is achieved by the involvement of enzymes such as phytases and phosphatases in the ruminants while these enzymes are absent in monogastric animals (Angel et al., 2002; Wienhold and Miller, 2004). Therefore, monogastric animals are dependent on much higher doses of external P supplements in their diet for their normal growth. This was also reflected in much higher excretion levels of P in their manures than in both cattle manures. As far as the influence of waste processing was concerned, we used fresh HM without any treatment, while TL had considerable bedding material mixed with the excreta and SS was aerobically digested with lime added as a stabilizing agent during waste processing. These treatments had caused a reduction in the levels of Bray1 in the TL and SS compared to HM. Previously, Cooperband and Ward Good (2002) had identified the presence of biogenic minerals of lower solubility in the waste from TL which resulted in much lower levels of water soluble P when mixed with soils than when mixed with cattle manure. Similarly, Haynes and Judge (2008) reported a presence of large amounts of CaCO3 in the poultry manures which ameliorated the acidity of the surface soil. Moreover, spreading of hydrated lime to control pathogens is also a common practice which leads to higher levels of calcium in the bedding material (Bennett et al., 2005). When gross Bray1 concentrations of P sources were expressed as a percentage of total P (Table 1), the relative distribution was HM ≥ CM2 > CM1 > SS > TL. Total P concentrations for TL and SS were higher than that of the remaining P sources but the proportion of that P extractable with Bray extract was much lower. In fact, both HM and CM2 had nearly 54% of the total P in Bray1 pool while CM1 contained 49% but SS and TL had only 29 and 25% of the total P, respectively. These results suggest that addition of these P sources to soil on an equal P basis might cause varying effects on Bray 1 concentrations. This was also reflected in the calculations of the expected increase in Bray 1 levels that might result when mixed at either 50 or 150 mg P kg−1 (Table 1). Turner and Leytem (2004) found that HM contained 78% of the total P in water soluble and NaHCO3 extractable fractions with corresponding values of 55% in cattle manure and 33% in TL. The results for their sum of both labile pools are in close agreement with the results in this study. Turner and Leytem (2004) also discovered that reactions of P with Ca were important in controlling P solubility. Manures with relatively high concentrations of water – or NaHCO3 – extractable Ca also had a high proportion of P present in easily extractable forms. Conversely, manures requiring an HCl solution to extract significant amounts of Ca also had a low proportion of P present in easily extractable forms. Toor et al. (2005) suggested that increased levels of dietary Ca resulted in higher levels of insoluble Ca–P precipitates in manure and litters. Further, Kalbasi and Karthikeyan (2004) added Fe, Al and Ca salts to different animal manures and found that manures treated with Al and Fe had lower amounts of Bray1 extractable P than manures stabilized with Ca.

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3.2. Interactive effect of P source and doze of application on Net Bray 1 concentrations at T0 (NBP0) The application of TSP at 150 mg P kg−1 resulted in 139.5 and 136 mg P kg−1 of NBP0 in the Wabash and Woodson soil respectively, which were the highest means, and significantly different from all other treatments (Table 2). Among the Po sources applied at the 150 mg P kg−1, the highest NBP0 was 83.2 mg P kg−1 found with CM1 amended Crete soil which was significantly different from most Po source treatments, except the Woodson soil amended with CM1, CM2 and SS as well as HM amended Crete soil which were not significantly different. The lowest value of NBP0 for the 150 mg P kg−1 application was 25.2 mg P kg−1 for TL amended Eram–Lebo soil which was significantly lower than most other P source/soil combinations at the same level of P application, but was not statistical different when compared to SS amendment of the same soil (27.8 mg P kg −1) and with TL amended Wabash, Ulysses, and Harney soils. The comparison of P sources at the highest P application dose suggests that TL resulted in significant lower values of NBP0 across all soils compared to the other P sources (Table 2). The only exceptions were SS amended Ulysses and Harney soils which were statistical at par with TL in the respective soils. Applications of all P sources in the Eram–Lebo and Harney soils resulted in lower amounts of NBP0 and were statistical at par with each other. The only exception was CM2 which had significantly more (48.9 mg P kg−1) NBP0 in the Harney than in the Eram–Lebo soil (36 mg P kg−1). Most Po sources within each soil were also statistically identical to each other. However, there were few exceptions such as TL which produced significantly lower amounts of NBP0 compared to other Po sources in most soils and the other treatment was SS amended Harney soil which had significantly lower concentrations than the CM2 in the same soil. As far as the response of various P source treatments at P applications of 50 mg P kg−1 was concerned, the Harney soil amended with TSP resulted in 49.5 mg P kg−1 of NBP0 and was significantly different from all treatments at the same level of P application. The CM1 amended Harney and SS amended Woodson soil resulted in 26.9 and 25.1 mg P kg−1 of NBP0, respectively, and these means were the highest among the Po sources and were significantly different from most P source treatments in the Eram–Lebo, Wabash and in Harney soils. The TL consistently produced lower values of NBP0 compared to other P sources, but unlike at the higher level of P application, less variability in the amount of NBP0 was found for most P sources across all soils. We recovered >90% of the total P applied as TSP at 150 mg P kg −1 in the Wabash and Woodson soil as net Bray1 (Table 2 and Table S2 supporting information) followed by 49, 40, 31 and 26% in Ulysses, Crete, Harney and Eram–Lebo soils, respectively. The TSP had 100% of the P in water and citrate soluble fractions that were easily extractable by the Bray1 solution, especially in the Wabash and Woodson soils. More recovery in both soils suggested that P from TSP remained in water soluble form and/or loosely held onto the surfaces of soil constituents and easily displaced with the fluoride ions supplied by Bray1 solution. This seemed to be true in the case of the Woodson soil which had the highest sand content among all soils and thus would have the least surface adsorption reactions. The greater recovery in Wabash soil might be attributed to the presence of soluble organic compounds in the soil solution owing to its highest soil organic matter (SOM) content among all soils in the study (32 g kg−1). Evidence suggests that these soluble organics generally compete with orthophosphate in the soil solution for surface adsorption reactions (Inskeep and Silvertooth, 1988). The lowest recovery of NBP0 was found in the Eram–Lebo and Harney soils. The Eram–Lebo soil had the lowest initial STP values (4.5 mg P kg−1) and highest clay content while Harney soils had the highest initial STP value (44 mg P kg−1) and pH, among all soils. Surface adsorption reactions onto mineral surfaces in the Eram–Lebo soil, while rapid precipitation of P into secondary precipitate of Ca and Mg in the Harney soil may explain the

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Table 2 Interactive effect of P source and levels of application on net Bray 1 concentrations at T0 (NBP0) in different soils.a P sources

P rates (mg P kg−1)

Eram–Lebo

Crete

Wabash

Woodson

Ulysses

Harney

27.5 20.5 y–e* (41%) 80.1 bc (53.4%) 22.5 x-c* (45%) 72.4 b–e (48.3%) 19.2 y–f* (38.4%) 50.3 j–o (33.5%) 18.7 y–g* (37.4%) 61.1 e–j (40.7%) 25.1 v–b* (50.2%) 77.0 b–d (51.3%) 46.0 l–s (92%) 136 a (91%)

23.0 19.1 y–g* (38.2%) 55.4 h–m (36.9%) 20.2 y–e* (40.4%) 68.5 c–g (45.7%) 13.9 b*–g* (27.8%) 36.5 q–v (24.3%) 16.4 z–g* (32.8%) 57.1 g–l (38.1%) 14.5 a*–g* (29%) 46.1 l–s (30.7%) 18.6 y–g* (37.2%) 73.2 b–e (48.8%)

44.4 26.9 u–a* (53.8%) 46.3 l–s (30.8%) 23.3 w–c* (46.6%) 48.9 j–q (32.6%) 13.6 b*–g* (27.2%) 30.6 t–y (20.4%) 14.6 a*–g* (29.2%) 42.1 n–t (28.1%) 13.5 b*–g* (27%) 37.4 p–v (24.9%) 49.5 j–p (99%) 46.5 l–s (31%)

mg P kg−1 b

CM-1

0 50 150

CM-2

50 150

TL

50 150

HM

50 150

SS

50 150

TSP

50 150

4.6 7.4 f*g* (14.8%)c 34.5 s–x (23%) 8.1 e*–g* (16.2%) 36.0 r–v (24%) 6.7 g* (13.4%) 25.2 v–b* (16.8%) 9.6 d*–g* (19.2%) 35.1 s–w (23.4%) 8.7 e*–g* (17.4%) 27.8 u–z (18.5%) 9.3 d*–g* (18.6%) 39.3 o–u (26.2%)

23.8 17.1 z–g* (34.2%) 83.2 b (55.5%) 18.9 y–g* (37.8%) 65.5 d–h (43.6%) 13.0 b*–g* (26%) 44.3 m–s (29.5%) 16.8 z–g* (33.6%) 72.0 b–f (48%) 17.9 z–g* (35.8%) 63.2 e–i (42.1%) 21.3 y–d* (42.6%) 59.6 f–k (39.7%)

21.4 12.5 c*–g* (25%) 44.9 l–s (29.9%) 12.3 c*–g* (24.6%) 47.9 k–r (32%) 8.0 e*–g* (16%) 37.5 p–v (25%) 9.1 d*–g* (18.2%) 52.1 i–n (34.7%) 14.5 a*–g* (29%) 54.5 h–n (36.3%) 22.0 x–c* (44%) 139.5 a (93%)

a Soil×P rate×P source interaction effect on net Bray1 concentrations at T0 is significant at Pb 0.01. Means with the same letter/letters in columns and across rows are not significant at Pb 0.05. Means with letters having dash line (−) represent all letters present between the two alphabets. Means with letter containing * symbol represent letter starting after z. b Bray 1 concentrations in the control treatments. Total P uptake from control treatments during seven harvests are included for comparative purpose. See Table S1-supporting information. c Parenthesis contains values indicating proportion of net Bary1 as percent of total P added at time zero in the respective treatments.

relatively low increases in Bray 1 extractable P after P additions. Both mechanisms can reduce the bioavailability of P to crops and the efficiency of applied P fertilizer (Sposito, 2008). The results of increases in NBP0 agreed with the Bray1 levels in animal manures when expressed as percent of the total P and not with the gross P extracted from these P sources. Any deviation of NBP0 from the expected Bray1 levels (Table 1) upon addition to the soil might reflect various soil and P source interactions that might either lower or increase the levels of NBP0. Both cattle manures and HM had almost 50% of the total P in the Bray 1 fraction but Crete soil amended with CM1 and HM and Woodson soil amended with both cattle manures at 150 mg P kg −1 were the only treatments where we extracted similar proportions (~50% of the total P) as found in these P sources prior to mixing with soils. The Woodson soil showed the greatest extractability where most Po sources had >40% of the total P as NBP0 (Table 2 and Table S2 supporting information), in all other soils it ranged from 25 to 33% for the three animal manures (CM1, CM2 and HM). However, the results for TL and SS were following different trends as both had b30% of the total P extracted with Bray 1 solution prior to mixing with soil. However, the amount of P extracted in SS amended Crete and Woodson soil mixed with highest dose of P application were 40 and 50% of the total P respectively, while it ranged from 19% to 34% in other SS treatments with the lowest values in the Eram–Lebo soil and highest in the Wabash soil, respectively. For TL, the Eram–Lebo soil had the lowest (17%) and the Woodson soil the highest (33%) recovery of NBP0, while all other treatments had extractable proportions similar to that found in TL (~25%) prior to mixing with soil. These results suggest that the nature of P in the TL is such that soil properties have minimal or no effect on Bray 1 extractability. Conversely, SS which also had b 30% of the total P in the Bray1 fraction, when mixed with Woodson and Crete soil resulted in greater extractability (42 and 50% respectively). Partial support for these differences was provided by He et al. (2010) where it was found that TL had most P associated with Ca, while SS not only had more P associated with Ca but significant higher P was also found associated with metals such as Al, Fe, Zn and Mn. Moreover, the solubility of P was mostly

controlled by reactions of calcium with P in the animal manures (Cooperband and Ward Good, 2002) but once mixed with soils it might shift from calcium to aluminum and iron oxides. Moreover, the nature of calcium associated P would also differ between the P sources as well. For example, Cooperband and Ward Good (2002) identified biogenic Ca and Mg phosphates of low solubility in TL as compared to cattle manure which resulted in lower water soluble P when added to soil. The NBP0 ranged from 17 to 26% of total P at the higher level of P addition and from 13 to 18% at the lower level of P application in the Eram–Lebo soil (Table 2). The corresponding proportion of Bray1 of the P sources not extracted ranged from 8 to 28% at the higher level and between 12 to 36% of the total P at the lower level of P application respectively. However, much higher values of NBP0 that ranged from 33 to 54% at higher level and between 38 to 50% at lower level for most Po sources were found in the Woodson soil. In fact >90% of the total P added from TSP at higher level was extracted in Bary1 in this soil. Moreover, an increase of 8 to 20% at higher level and between 13 to 20% of the total P at lower level was monitored for TL and SS respectively. Regarding cattle manures in Woodson soil, it stayed the same (~ 50%) at higher but decreased by 10% at the lower levels of P application. Similarly, ~ 10% reductions in Bray1 from HM amended treatments were also monitored at both levels of P application. The effect of high initial STP (44.4 mg P kg −1) became more evident in the Harney soil where most Po sources at lower level of P application released near identical proportions of Bray1 as contained in themselves. The only exception was HM which showed a reduction of 24% in the Bray 1 extractable P. However, at higher level of P application, nearly all P sources had shown a reduction in Bray 1 concentrations that ranged from as low as 5% for TL and SS treatments to ~ 20% for the rest of Po sources and reduction as high as 60% of the total P was reported in the TSP treatment. The reasons for these variations in net Bray 1 in these three soils are already explained in the aforementioned paragraphs. Most Po sources had shown a reduction of nearly 25% in the Bray 1 at higher level and between 10 to 35% at lower level of P application compared to P sources alone in Wabash

M.N. Shafqat, G.M. Pierzynski / Catena 105 (2013) 21–28

soil. This soil had the highest SOM (32 g/kg) among all soils and indigenous soluble organics might play a role in decreasing the adsorption of added inorganic P as would be the case for TSP. The Ulysses and Crete soil had identical initial STP values but variations in the results could be attributed to the high pH of Ulysses soil which might neutralize some of the extracting power of Bray1 solution. 3.3. Interactive effect of P source and dose of application on Net Bray 1 concentrations at T7 (NBP7) The results regarding the influence of P sources applied at different doses on the levels of NBP7 for six different soils are presented in the Table 3. The Crete soil amended with TSP at 150 mg P kg−1 resulted in 36.5 mg P kg−1 of NBP7 which was the highest value and was significantly different from all treatments in the study. Among the Po sources, the Woodson soil amended with SS at the highest level of P application had 19.6 mg P kg−1 of NBP7 and was significantly different from all Po treatments in the study, the only exception being the Crete soil with the same treatment (NBP7 =18.6 mg P kg−1). The concentrations of NBP7 resulted from the application of CM2 at the aforementioned dose were 7.0, 5.6, and 7.6 mg P kg−1for the Eram–Lebo, Ulysses and Harney soils respectively, and were statistically at par with each other but were significantly different from the Crete, Wabash, and Woodson soils which were at 14.3, 13.1 and 10.9 mg P kg −1 respectively. Trends similar to CM2 were seen for the rest of Po sources applied at 150 mg P kg−1. However, the values of NBP7 for TSP at 150 mg P kg−1 in the Crete and Wabash soils were 36.5 and 23 mg P kg−1 respectively, which were not only significantly different from each other but also different from other soils receiving the same amendment as well. At the lower dose of P application (50 mg P kg −1), TSP amended Crete soil had a NBP7 concentration of 7.1 mg P kg −1 and was significantly different from all treatments with exception of TL and SS amended Woodson soils which had NBP7 concentrations of 5.2 and

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3.9 mg P kg −1, respectively. All other P sources at this P application dose resulted in statistical similar amounts of NBP7. Finally, NBP7 concentrations for all P sources at 150 mg P kg −1 level were significantly higher compared to that at lower level (50 mg P kg −1) used in the study. When data on NBP7 was converted into the percentage of the residual P (Table 3 and S2 supplementary information), the Crete soil amended with TSP had 19 mg P kg −1 of residual P and out of which NBP7 made up of 38%. In fact, the Crete soil amended with TSP had identical levels of NBP7 (38%) when expressed in percent of the residual P despite the large difference in amount of residual P at lower level of P addition (19 mg P kg −1) compared to the higher level of P application (106 mg P kg −1). This value (38%) was also identical to what was seen at T0 suggesting the nature of interactions of soluble P from TSP with the soil constituents were such that near identical P amounts were extractable both prior to crop P removal and after the seventh harvest. As far as the Po sources at lower level of P application were concerned, the Woodson soil amended with SS had the highest contribution of its residual P (26.6 mg P kg −1) towards %NBP7 (14.6%) while the lowest was negligible (0.1%) in both TL amended Eram–Lebo and Ulysses soils, despite having different final amounts of residual P, 34.5 and 28.8 mg P kg −1 for both soils, respectively. In fact, all soils amended with TL contained more residual P but least of it was contributed towards %NBP7 (range from 0.1 to 7.0 mg P kg −1) in comparison to the other P sources. However, nature of P in the HM was such that most of P added was taken up by the plants and resulted in the lowest amount of residual P which ranged from as low as 12 mg P kg −1 in the Ulysses soil to as high as 25 mg P kg −1 in Wabash soil at the lower level of P application. At higher level of P application, the TL had the greatest amount of residual P that ranged from 97 to 114 mg P kg −1 and the lowest % of NBP7 while HM had the lowest residual P which ranged from 55 to 82 mg P kg −1 but larger proportion of the residual P (~18%) was

Table 3 Interactive effect of P source and levels of application on net Bray 1 at T7 (NBP7) in different soilsa. P sources

P rates (mg P kg−1)

Eram–Lebo

Crete

Wabash

Woodson

Ulysses

Harney

10.0 (40.0) 2.0 v–z (23.0-8.7%) 14.9 d–f (87–17.1%) 2.0 v–z (27.9-7.2%) 10.9 g–m (87–12.5%) 5.2 p–x (36.2-1.4%) 13.9 e–h (108–12.9%) 1.4 yz (20–6.9%) 10.9 g–m (58–18.7%) 3.9 q–y (26.6-15%) 19.6 bc (78–25.1%) 2.4 u–z (19–12.6%) 13.9 e–h (48-28%)

12.2 (20.0) 0.4 yz (21.7-1.8%) 7.2 m–r (85–8.4%) 0.01 z (23–0.04%) 5.6 p–v (80–7.0%) 0.03 z (28.8-0.1%) 5.3 p–w (106–5.0%) 0.6 yz (12.3-4.5%) 9.4 i–o (55–17.1) 0.3 yz (18.7-1.6%) 7.7 l–p (79–9.7%) 2.2 v–z (32.5-6.7%) 15.4 de (108-14%)

19.0 (37.0) 1.4 yz (25.8-5.4%) 9.0 j–p (92–9.8%) 0.6 yz (24.2-2.4%) 7.6 l–q (87.6–8.7%) 1.0 yz (32.7-3.0%) 6.3 o–t (111–5.6%) 1.3 yz (14.6-8.9%) 11.3 f–l (70-16%) 1.0 yz (22.9-4.3%) 8.3 k–p (83–9.9%) 3.3 s–z (27.6-12%) 15.3 de (102-15%)

mg P kg−1 b

CM-1

0 50 150

CM-2

50 150

TL

50 150

HM

50 150

SS

50 150

TSP

50 150

c

3.45 (21.0) 1.0 yz (30.1-3.3%)d 6.7 o–s (94.5-7.0%) 0.4 yz (29.5-1.3%) 7.0 n–s (94–7.4%) 0.3 yz (34.5-0.1%) 3.8 r–y (106–3.5%) 0.8 yz (21–3.8%) 6.0 o–u (82–7.0%) 1.3 yz (28.5-4.5%) 8.1 k–p (106–7.6%) 1.5 x–z (22.7-6.6%) 14.5 e–g (106-15%)

5.5 (50.0) 2.4 u–z (34.0-7.0%) 12.2 e–j (91–13.5%) 2.8 t–z (35–8.0%) 14.3 e–g (102-14%) 2.8 t–z (40–7.0%) 10.6 h–n (114–9.2%) 1.7 w–z (23–7.4%) 14.2 e–h (74–19.2%) 3.5 r–z (27.7-13%) 18.6 dc (97–19.1%) 7.1 m–r (19.2-38%) 36.5 a (106-38%)

7.5 (34.0) 0.9 yz (28.8-3.1%) 11.7 e–k (95–12.3%) 0.6 yz (32.7-1.8%) 13.1 e–I (95–13.8%) 1.5 x–z (33.5-4.4%) 12.1 e–j (97–12.4%) 0.3 yz (25–1.1%) 11.0 g–l (79–13.8%) 2.7 t–z (27.3-9.8%) 15.3 de (96–16.2%) 2.8 t–z (27.6-10%) 23 b (95-24%)

a Soil×P rate×P source interaction effect on net Bray P concentrations at T7 is significant at Pb 0.01. Means with the same letter/letters in columns and across rows are not significant at Pb 0.05. Means with letters having dash line (−) represent all letters present between the two alphabets. Means with letter containing * symbol represent letter starting after z. b Bray 1 concentrations in the control treatments. c Total P uptake from control treatments during seven harvests are included for comparative purpose. See Table S1-supporting information. d Bold face values refers to the amount of residual P left at the end of seven harvest in each treatment, while italic values refers to the proportion of net Bray1 as percent of remaining residual P in each treatment.

26

M.N. Shafqat, G.M. Pierzynski / Catena 105 (2013) 21–28

extractable with Bray 1 solution. The Eram–Lebo and Harney soils amended with P sources had residual P values that contributed lowest proportion towards NBP7 compared to other soils. Surface adsorption of P in the Eram–Lebo soil and precipitation reactions and formation of more stable secondary precipitates of lower solubility in the Harney soils might be the contributing factors. Both cattle manure had near identical percent values of NBP7 as well as the amounts of residual P suggesting similar characteristics of P contained in both manures and their subsequent reactions with the soil constituents. The SS amended Woodson soil was unique because it had the least residual P at both levels of SS application but still a considerable proportion was contributed towards NBP7 in this soil compared to other soils used in this study. 3.4. Interactive effect of P source and dose of application on Net Bray1 concentrations at T1 (NBP1) There has been an increasing utility of agronomic STP for the purposes of environmental monitoring especially in the past decade emphasizing the need to study changes in STP following removal of easily bioavailable P from an animal or fertilizer P source in the first growing season or the first harvest. Generally, the reduction in STP after the first harvest might reflect the lower availability of P for the subsequent crops in the cycle. However, when we consider using the same STP value for environmental purposes, the magnitude of reduction or increase following the crop harvest resulting from residual P might also indicate the levels of risk that a particular soil might pose regarding offsite P movement to the nearby fresh water resource. The data regarding the interactive effect of P source and levels of application on NBP1 are presented in Table 4. The Wabash soil amended with 150 mg P kg −1 with TSP resulted in 78.1 mg P kg −1 of NBP1 and was significantly different from all treatments included in the study. Similarly, the Harney soil amended with the

same level of TSP and the Crete soil amended with HM and CM1 resulted in NBP1 levels of 70.6, 65.1 and 64.1 mg P kg −1 in decreasing order respectively and were significantly higher than all other treatments in the study but not statistically different from each other. As far as a given Po source across all soils was compared at the 150 mg P kg −1 level of addition, both cattle manures (CM1 and CM2) resulted in the highest concentrations at 55.1 and 64.1 mg P kg −1of NBP1 in the Crete soil, respectively, while the highest concentrations were 65.1 and 53.5 mg P kg −1 for the HM and SS, respectively, found in the Crete soil and were significantly different from the treatments receiving the same P source across all soils. However, the few exceptions were the Woodson soil amended with CM1 and SS which were not statistically different from each other. Contrary to the above, the TL amended Woodson and Crete soils had NBP1 levels of 36 mg P kg −1 and were statistically equivalent to TL application in Harney soil but statistically different from the rest of the soils. The basic trends were similar to what we had reported under NBP0, with TL that resulted in significantly less amounts of NBP1compared to the other sources. However, there were some treatments where relative to NBP0, we found an increase such as in Harney soil amended with TSP or had the similar amounts of Bray1 such as in all other P source treatments applied at 150 mg P kg −1 in the Harney soil. The magnitude of decline in Bray 1 for all the P sources was small after harvest 1 relative to T0 in the Eram–Lebo soil compared to the other soils. The trends at the lower level of P application were similar to what were reported at T0. However, the Harney and Woodson soils amended with TSP were showing the greatest reductions in NBP1 relative to NBP0 where the values of net Bray were decreased from 49 and 46 mg P kg −1 to 17.6 and 19.6 mg P kg −1, respectively. As far as the data on the percentage of the residual P contributed towards NBP1 were concerned (Table 4 and S2 in supplementary information), the treatments which had the highest amounts at T0 (Woodson soil amended with TSP at both levels and Wabash soil

Table 4 Interactive effect of P source and levels of application on net Bray 1 at T1(NBP1) in different soilsa. P sources

P rates (mg P kg−1)

Eram–Lebo

Crete

Wabash

Woodson

Ulysses

Harney

21.3 (17.0) 12.6 x-c* (38.4-33%) 51.3 d-g (133–38.6%) 11.6 z-d* (41.7-28%) 50.3 d-g (130–38.6%) 10.3 z-f* (44–23.5%) 36 k-n (137-26%) 11.0 z-e* (36.3-30%) 43.3 h-j (104-42%) 15.0 v-z (41.6-36%) 51.6 d-f (120-43%) 19.6 t-v (32.8-60%) 55.6 d (93-60%)

17.0 (8.0) 11.0 z-e* (37.8-29%) 47.3 f-h (133–35.6%) 13.3 w-b* (38.7-34%) 52.3 d-f (126–41.5%) 6.3 d*-h* (42-15%) 25.0 r-t (135–18.5%) 10.0 z-g* (32.3-31%) 43.6 h-j (106-41%) 9.6 z-g* (38-25%) 34.6 m-o (127-27%) 18.0 u-x (44.6-40%) 40.0 j-m (133-30%)

33.3 (17.0) 19.3 uv (43.3-45%) 48.0 e-h (135–35.5%) 18.6 u-w (40.9-46%) 47.3 f-h (130–36.3%) 10.3 z-f* (44-23%) 32.0 n-q (138-23%) 14.3 v-a* (37.2-38%) 43.3 h-j (121-36%) 11.6 z-d* (42-28%) 33.3 n-p (131-25%) 17.6 u-y (39.8-44%) 70.6 b (127-55%)

mg P kg−1 b

CM-1

0 50 150

CM-2

50 150

TL

50 150

HM

50 150

SS

50 150

TSP

50 150

c

4.1 (4.1) 5.0 f*-h* (39–12.6%)d 27.4 q-s (133–20.6%) 5.6 e*-h* (39.2-14%) 27.8 p-s (131-21%) 3.3 h* (41.7-7.9%) 11.7 z-d* (134–8.7%) 4.7 g*h* (32.6-14%) 22.9 s-u (119–19.2%) 7.2 c*-h* (39.1-18%) 25.1 r-t (139-18%) 6.2 d*-h* (36.8-17%) 29.9 o-r (128-23%)

18.8 (22.0) 12.3 y-c* (47.6-26%) 55.1 d (139–39.6%) 14.7 v-z (49.5-30%) 64.1 c (147–43.6%) 6.5 d*-h* (49.3-13%) 35.5 l-n (145–24.5%) 13.4 w-a* (40–34.2%) 65.1 bc (130–49.9%) 9.9 z-g* (44.5-22%) 53.5 de (142-38%) 7.1 c*-h* (46–15.4%) 35.1 l-o (135-26%)

16.8 (8.0) 9.5 z-g* (41-23%) 39.1 j-m (134–29.2%) 10.1 z-g* (45.2-22%) 45.8 g-i (135-34%) 7.8 b*-h* (44.8-17%) 30.5 n-r (132-23%) 8.8 a*-h* (38.5-23%) 40.2 j-l (117-34%) 11.5 z-d* (40.6-28%) 41.5 i-k (129-32%) 11.1 z-e* (39.8-28%) 78.1 a (126-62%)

a Soil×P rate×P source interaction effect on net Bray1 P concentrations at T7 is significant at Pb 0.01. Means with same letter/letters in columns and across rows are not significant at Pb 0.05. Means with letters having dash line (−) represent all letters present between the two alphabets. Means with letter containing * symbol represent letter starting after z. b Bray 1 concentrations in the control treatments. c Total P uptake from control treatments during seven harvests are included for comparative purpose. See Table S1-supporting information. d Bold face values refers to the amount of residual P left at the end of seven harvest in each treatment, while italic values refers to the proportion of net Bary1 as percent of remaining residual P in each treatment.

M.N. Shafqat, G.M. Pierzynski / Catena 105 (2013) 21–28

amended with TSP at 150 mg P kg −1) still had the highest percent of Bray 1 (~ 60%). However, the same treatments also showed the largest decrease in percent Bray 1 following harvest 1 (~ 30%). The Harney soil amended with TSP at 150 mg P kg −1 was the only treatment that was showing a nearly two fold increase in net Bray 1 from 30 to 55.1% after the harvest 1. In fact all P sources when applied at 150 mg P kg −1 in the Harney soil resulted in increase of net Bray 1 that ranged from 3 to 5% of the residual material after harvest 1. The greatest reductions were evident in TL amended Eram–Lebo soils at both levels of P addition along with Crete and Ulysses soil amended with 50 mg P kg −1 which were almost showing a 50% reduction in percent net Bray 1 contributed by the residual TL following harvest 1 when relative data in the respective treatments were compared prior to the crop P removal. However, the TL was the only P source which had the lowest percentage of NBP1 (~ 23%) under most soils compared with the other P sources used in the study. All Po sources at both levels of P application nearly had the same proportion of net Bray 1 both before and after harvest 1 in the Wabash soil, while HM amended with both doses across all soils also maintained similar proportion towards net Bray 1 when both times were compared on relative scale. Therefore our results suggest that soils testing high in available P initially, plus receiving P at the highest level of addition, might show higher STP following harvest 1 than prior to crop P removal. Similarly, the P sources such as HM might maintain similar levels of net Bray 1 both at T0 and T1. The least residual P was seen with HM amended soils and the most was found with TL among the Po sources. Interestingly, the nature of residual P in the TL was such that it was contributing the least towards the Bray 1 while in HM after harvest 1, residual P contained significant higher proportion of net Bray 1 despite luxury consumption of soluble P in the HM amended soils. Therefore, it is helpful to be aware of the nature of residual P as it would influence the net Bray 1 after crop harvest. But it does seem that soil having low initial STP levels with high clay contents such as Eram–Lebo, might not be a concern as well as soils receiving TL and in some cases SS might not contribute too much towards net Bray 1 after the first harvest. However, soils such as Woodson and Wabash which were either high in sand or organic matter receiving TSP might contain large proportion of residual P in pools of STP. The same is true for soils containing high initial STP which might cause greater solubility of added P following crop removal of P. And finally, the P sources which might have a greater percentage of Bray 1 concentration might have the propensity to maintain higher contribution towards Bray 1 both prior and after the first harvest. This variable amount of reduction for different P sources at T1 had important significance from both agronomic and environmental perspective. For the P sources which had the greatest reductions following harvest 1 would be considered beneficial as lower values in STP would likely pose lesser risk for the offsite P transfer. But form an agronomic perspective, a rapid reduction after harvest 1 would mean greater probability of the need for additional P to support crop growth.

4. Conclusion The monogastric P sources contained relatively large concentrations of Bray 1 than P from P sources originating in ruminants. However, when gross Bray 1 levels were expressed as percentage of total P, the HM and CM2 had identical proportion while SS and TL had the least amount of Bray 1 extractable P. Both cattle manures and HM resulted in significant higher concentrations of NBP0 and NBP1 in most soils among the animal P sources. All P sources in Eram–Lebo soil and all soils amended with TL at both levels of P application had the least amounts of NBP0 and NBP1. The greatest proportion of total residual P was detected as Bray 1 in HM and the least in TL in this study.

27

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