Seasonal Changes in Phosphorus and Phosphatase Compositions in Soils enriched with Broiler Litter

1. Seasonal Changes in Phosphorus and Phosphatase Compositions in Soils enriched with Broiler Litter R.N. Mankolo1, Z.N. Senwo and T.D. Ranatunga1 1 Department of Plant and Soil ScienceAlabama A&M University, Normal, AL, 35762 ABSTRACT CONCLUSION In the United States, the poultry industry generates over 50% of the agricultural profits while utilizing nearly 80% of the grain produced for feeds. An estimated 1 kg of litter is generated for each kg of broiler litter produced and of which over 90% is land applied. Laboratory analyses were conducted to quantify phosphorus (P) and phosphatase compositions in soils enriched with broiler litter. Results indicated that the various P forms decreased with depth and were significantly (P < 0.01) affected by season. The lowest phosphatase activity occurred in fall compared to spring. Phosphatase activity was affected by depth in the first year compared to year two. Phosphorus fractionation was performed on each soil using the scheme developed by Hedley et al. (1982) and modified by Tiessen and Moir (1993). The Po fractions (H2O, HCl, NaHCO3, NaOH, and H2SO4) were extracted sequentially and measured with inductively coupled plasma emission spectroscopy (ICP-AES), while, Pi was measured colorimetrically (Murphy-Riley,1962). The approach to assay for phosphatase activity is described by Tabatabai (1994). It involves the extraction and quantitative determination of μg p-nitrophenyl released when soil is incubated with p-nitrophenyl phosphate or bis-p-nirtophenyl phosphate in MUB adjusted to pH 6.5, 11, and 8 for acid and alkaline phosphomonoesterase and phosphodiesterase . Enzyme activities were assayed on < 2 mm field-moist samples in duplicate and control and expressed on a moisture- free basis. Statistical analyses were performed to assess the effects of soil depth and sampling time on soil P fractions (SAS/STAT, 1996). Least significant difference analysis (LSD) was performed for mean separation. The decrease in phosphatase activity with depth can be attributed to decreased biological activity. Overall, high P fractions and phosphatase activity under warm conditions indicates that factors such as temperature and plant development significantly affected the activity of microbial populations which apparently influence P mineralization. Broiler litter application tends to promote the formation of less Po fractions at the expense of more Pi through mineralization.Our results indicate there was consistently higher inorganic (>36 to 63%) than organic (13 to 17%) P in treated surface soil (0– 5 cm). More total P was accumulated in the non-labile (49 to 57% ).   Results Cont’d. The depth and time affected NaOH-Po fraction and showed the highest P content with the soil surface and subsoil for both season. However the warm season showed larger increase in NaOH-Po but a smaller increase for the cold season. The difference among season was observed during the first year. This fraction was not found significant among treatments in the first and second years.The increase in soil NaOH-Po over time and season may be explained by the P source and probably the decomposition and release of easily hydrolysable Po compounds in BL. The distribution of NaHCO3-Po for the two surface layers showed lower P contents compared to the inorganic forms and to the NaOH-Po fraction under the two years. The increase of NaHCO3-Po in cold season the second year was greater than what was observed the first year although some of the increases were not statistically significant. Similarly different trends in NaHCO3-Po was found under warm conditions where less NaHCO3-Po was observed (Guo et al., 2000). The HCl-Po constitutes stable Ca bound P assumed to be less available to plants (Williams et al. 1980). This constituted the greatest P fractions in summer months. INTRODUCTION REFERENCES In the last decade, poultry production has significantly increased due to world population growth and the high demand for low-fat meat. Poultry industries generate huge amounts of wastes yearly. Since large poultry growers are located in small geographic areas of Georgia, Alabama, Mississippi, North Carolina, Texas, Oklahoma, Delaware, Maryland and Virginia, use of broiler litter (BL) on agricultural lands has generated several environmental concerns. The application of BL to meet the P needs for crop production has been used in several countries resulting in increased amount of total and available P in receiving soils (Siddique and Robinson, 2003). Knowledge of various P forms in soils may help to predict risk of P transfer from soil to water systems, plant uptake and bioavailability (Zheng et al., 2004). Organic manuring has advantages when incorporated in soil as sources enzymes for microbial processes. Phosphatases hydrolyze organic compounds into inorganic P. The activity of phosphatases may not directly measure P status, but may release a significant portion of P for plant use (McCallister et al.2002). Soil enzyme activities proposed as a biological index of soil quality are sensitive to management-induced changes in soil with time (Bregstorm et al., 1999). This study assessed time, season and depth on changes in soil P and phosphatase compositions in soils enriched with broiler litter for over 20 years. Barnett, G.M. 1994. Phosphorus forms in animal manure. Bioresour.Technol.19:139-148. Bergstrom, D.W. , C.M Monreal, A.D. Tomlin, and J.J. Miller. 1999. Interpretation of soil enzyme activities in a comparison of tillage practices along a topographic and textural gradient. Can. J. Soil Sci. 80:71-79. McCallister, D.L., M.A. Bahadir and J.M. Blumenthal. 2002. Phosphorus partitioning and phosphatase activity in semi-arid region soils under increasing crop growth intensity. Soil Science. 167:616-624. Sistani K.R., G.E. Brink, A.Adeli, H.Tewolde, and D.E. Rowe. 2004. Year-round nutrient dynamics from broiler litter appli8cation to three Bermuda grass cultivars. Agron. J. 96:525-530. Tabatabai M.A (1994) Soil enzymes.In: weaver R.W.,Angle J.S, Bottomley PS (eds) Methods of soil analysis, part 2. Microbiological and biochemical properties. SSA Book Series No. 5. Soil Sci Soc Am, Madison, Wis., pp 775-833 Zheng, Z., J.A. Macleod, J.B. Sanderson and J. Lafond.2004 Soil phosphorus dynamics after ten annual applications of mineral fertilizer and liquid dairy manure: Fractionation and path analysis. Soil Science.169:449-456. Significant at P ≤ 0.05 level. ** Significant at P≤ 0.01 level. NS, not significant at the P≤ 0.01 level. Acid Ptase =acid phosphatase Alkaline Ptase= alkaline phosphatase Diest Ptase=phosphodiesterase RESULTS Inorganic P fractions Significant effects of year, depth, and season of sampling were found with inorganic P fractions with the exception of NaOH-Pi in which there was no year effect with warm season and NaHCO3-Pi in which neither year or depth were found significant (Table 2). The increase in NaOH-Pi over time in this study could be the result of slow P sorption to Fe and Al oxide surfaces from the large amount of applied P resulting in the release of phosphate ions from both organic and inorganic forms (Zhang and MacKenzie, 1997). In the cold season, H2O soluble P was not significantly affected by year or depth.Water-soluble inorganic P concentrations were higher for the warm than the cold season and greater in the subsurface soil for both years. This may be due to increased P mineralization from organic source due to higher temperatures. P concentrations for all fractions at the 0-5 to 5-10 cm depth of amended soil were greater than those at the same depth in the control for both years (Fig 1). The decrease in all P-fractions with depth indicated that P did move down in the soil profile. MATERIALS & METHODS The study site was initiated from 2000-2001 on a farm near Mize, Mississippi (31.8o N, 89.6oW). The soil at the site is fine sandy loam (fine-loamy, siliceous, semi active, thermic Typic Fragiudult). The area has been active since 1997 and has received BL for over 20 years. Surface soil layers (0-5 and 5-10 cm) were sampled in plots already established with three varieties of Bermuda grass (Common, Hybrids Coastal and Tifton 85). Soils were sampled in March and July 2000 and 2001. The two months are considered to be cold and hot months respectively. Broiler litter was collected from a nearby litter at each application and applied at rates of 15.75 Mg ha-1 yr-1. The rate of 9.0 Mg ha-1 yr-1 was applied in mid March and 6.75 Mg ha-1 yr-1 in mid July for both years. Thus, the amount of N, P, and K from the BL applied in 2000 and 2001 were: N, 535 and 408 kg ha-1; P, 337 and 319 kg ha-1; and K, 374 and 435 kg ha-1, respectively. The BL and soil chemical analyses were performed on dried samples and the results are shown on Table 1.