Date: Mon, 29 Mar 1999 15:25:56 -0600 From: "Wilson, Dale" Phosphorous Fixation Although P fixation can occur at neutral and alkaline pH by precipitation as calcium phosphate, fixation at low pH in highly weathered, especially tropical soils is much more serious. P is sequestered as iron and aluminum phosphates by reaction with metal ions and oxides. Most soil science texts have a section on this. A good discussion is found in "Properties and Management of Soils in the Tropics", by Pedro Sanchez, 1976, pages 254 - 294. P fixation is not all bad. In the vast majority of soils, phosphorus moves very slowly in the soil profile, so does not leach, although it is lost by soil erosion. No. Records Request 1 8860 spatial 2 5325 spatial in de 3 85420 soil 4 57989 soil in de 5 1332 #4 and #2 6 38347 nutrient 7 29879 nutrient in de * 8 178 #7 and #5 Record 1 of 14 - AGRICOLA 1998/01-1998/12 AU: Hodge,-A.; Stewart,-J.; Robinson,-D.; Griffiths,-B.S.; Fitter,-A.H. TI: Root proliferation, soil fauna and plant nitrogen capture from nutrient-rich patches in soil. SO: New-phytol. Cambridge : Cambridge University Press. July 1998. v. 139 (3) p. 479-494. CN: DNAL 450-N42 LA: English Record 2 of 14 - AGRICOLA 1998/01-1998/12 AU: Jama,-B.; Buresh,-R.J.; Ndufa,-J.K.; Shepherd,-K.D. TI: Vertical distribution of roots and soil nitrate: tree species and phosphorus effects. SO: Soil-Sci-Soc-Am-j. [Madison, Wis.] Soil Science Society of America. Jan/Feb 1998. v. 62 (1) p. 280-286. CN: DNAL 56.9-So3 LA: English AB: We hypothesized that trees can rapidly root into subsoil and capture NO3, which can accumulate in the subsoil of agricultural soils with high anion sorption. Th e vertical distribution of root length and inorganic N (NO3 and NH4) to 3.95-m s oil depth was compared for 11-mo-old stands of eucalyptus (Eucalyptus grandis W. Hill ex Maiden), sesbania [Sesbania sesban (L.) Merr.], calliandra (Calliandra calothyrsus Meissner), markhamia [Markhamia lutea (Benth.) Schumann], and grevil lea (Grevillea robusta A. Cunn. ex R. Br.) grown at two P levels (no added P and 500 kg added P ha-1) on a Kandiudalfic Eutrudox in Kenya. The trees were plante d at a 1 by 1 m spacing in a randomized complete block with three replications. Added P had no effect on root length, soil NO3, and soil NH4 even though the soi l was low in available P. Total root length was greater for calliandra (15.5 km m-2) than other trees (1.2-5.6 km m-2). The slope for the model of natural logar ithm root length density (cm cm-3) as a function of soil depth was affected by t ree species (P < 0.01), indicating differences among trees in the tendency for d eep rooting. Root length densities, averaged for the two P levels, were greater than or equal to 0.1 cm cm-3 to depths of 2.2 m with calliandra, 1.8 m with sesb ania, 1.2 m with eucalyptus, 0.45 m with grevillea, and 0.3 m with markhamia. Ca lliandra and sesbania reduced soil NO3 in the top 2 m by about 150 to 200 kg N h a-1 within 11 mo after establishment and effectively captured subsoil NO3. Fast- growing trees with high root length densities can rapidly reduce subsoil NO3. Record 3 of 14 - AGRICOLA 1998/01-1998/12 AU: Li,-F.M.; Cao,-J.; Wang,-T.C. TI: Influence of phosphorus supply pattern in soil on yield of spring wheat. SO: J-plant-nutr. Monticello, N.Y. : Marcel Dekker Inc. 1998. v. 21 (9) p. 1921-1931. CN: DNAL QK867.J67 LA: English AB: The purpose of this research was 1) testing the influence of various patterns of supplying phosphorus (P) on dry matter production and biomass allocation in various organs of spring wheat and 2) exploring the optimal P application pattern for high grain yields of spring wheat. Plants were grown in pots constructed with PVC tube, 130 cm long and 10 cm in diameter. Each tube consisted of two segments of 0-43 cm and 43-130 cm. Two soil water regimes were imposed: i) D, water content in the upper soil layer was kept at 50% of field capacity (FC), lower layer (43-130 cm) was at 75-80% of FC and ii) W, a well-watered control with the entire soil profile being maintained at 75-80 FC. Three P applications were made: i) Pu, P was supplied in the upper 0-43 cm soil layer, ii) Pl, P was supplied in the 43-130 cm layer, and iii) Pe, P was supplied to the entire soil profile. Total photosynthates of plants in WPe and WPu in a whole day were higher than that in DPe and DPu. The photosynthetic rates were similar between WPl and DPl. The highest P/T (Photosynthesis/Transpiration) in topsoil drying treatments occurred in DPu, but in wet treatments it was Wpe. The DPu and WPu had similar leaf area, which were significantly higher than other treatments. In the period from the beginning of water treatments to harvest, water consumption in DPe, DPu, DPl, WPe, WPu, and WPl was 419, 354, 476, 763, 565, 806 mL, respectively. At harvest time, supplied water use efficiencies of DPu and WPu were similar, and reached a peak in both drying and wet treatments. Grain weights per shoot in DPu and WPu were significantly higher than those of other treatments. This implies that phosphorus. supplied to the upper soil is beneficial to yield maximum. Record 4 of 14 - AGRICOLA 1998/01-1998/12 AU: Somda,-Z.C.; Powell,-J.M.; Bationo,-A. TI: Soil pH and nitrogen changes following cattle and sheep urine deposition. SO: Commun-soil-sci-plant-anal. Monticello, N.Y. : Marcel Dekker Inc. 1997. v. 28 (15/16) p. 1253-1268. CN: DNAL S590.C63 LA: English AB: The relationship between animal urine deposition and variability in soil chemical composition and crop growth is not well established in the semi-arid region of West Africa. This study was conducted to examine the changes over time in soil pH and mineral nitrogen (N)concentrations at the micro sites of cattle and sheep urine patches in comparison to those occurring in fertilizer urea placement zones. The urine and fertilizer solution containing each 400 mg N (800 kg N ha-1) were spread onto individual plots covering a surface area of 4-cm radius. The treatments included a control, which consisted of distillate water. Soil samples from three replicate plots were taken in 4-cm increments to a depth of 16 cm and distance of 16 cm on a grid pattern at days 1, 7, 21, 49, 90, 120, and 150 after application. Significant pH and mineral N gradients develop in the vicinity of the fertilizer and urine placement zones declining towards the periphery and the deeper soil layers. The pH at the center of the urine zone remained above 7.5 throughout the 150 days of the study period. After the initial increase, the soil pH below the fertilizer placement sites declined to the control level by day 90. Concentrations of ammonium (NH4) + nitrate (NO3) also increased markedly in the immediate soil layers of the urine and urea placement zones, and then decreased over time probably due to N losses by volatilization and leaching. Concentrations of mineral N at the periphery of the placement site were similar for all treatments throughout the study period, indicating very little lateral N diffusion. These results provided evidence that animal urine causes significant variabilities in soil chemical composition, even in. short distance from the deposition zones. The high soil solution pH in the vicinity of the urine patches alleviate the potential of aluminum (Al) toxicity while increasing the phosphorus (P) availability to crop plants. Record 5 of 14 - AGRICOLA 1998/01-1998/12 AU: Bly,-A.; Woodard,-H.J. TI: Soybean growth and yield response to residual fertilizer phosphorus bands. SO: J-plant-nutr. Monticello, N.Y. : Marcel Dekker Inc. 1997. v. 20 (11) p. 1527-1538. CN: DNAL QK867.J67 LA: English AB: Residual effects on soybeans (Glycine max L.) from phosphorous (P) fertilizer bands applied 5 cm to the side and 5 cm below the seeds of a preceding corn (Zea mays L.) crop on a Brandt silt loam soil (fine-silty, mixed Udic Haploboroll) were studied after an intervening no-till fallow period. The P rates applied were 0, 12, 24, and 49 kg P ha-1. Soybean rows were planted as close as possible to the preceding corn rows. Soybean tissue was sampled at the early bloom stage in each row of the paired-row design. Twenty soil column (2.5x3 cm) samples were collected from the 0-15 cm depth along a 50-cm-long trench that bisected a soybean row. The distance of the previous P band (column with the highest extractable Bray-I P level) from the soybean row became a variable in this experiment with category range distances of <6 cm, 6-9 cm, and >9 cm from band to row. Residual P from all application rates increased shoot dry matter weight, shoot P uptake, and to a lesser extent grain yield in comparison to the unfertilized soybeans. Distance of the P band from the row was more important than the P concentration in the band. Shoot P uptake and grain yield were significantly larger for fertilized compared to unfertilized soybeans when the band distance was less than 9 cm from the row. Residual P band distance of greater than 9 cm from the row had little effect on soybean growth and yield. Record 6 of 14 - AGRICOLA 1998/01-1998/12 AU: Jingguo,-W.; Bakken,-L.R. TI: Competition for nitrogen during decomposition of plant residues in soil: effect of spatial placement of N-rich and N-poor plant residues. SO: Soil-biol-biochem. Exeter : Elsevier Science Ltd. Feb 1997. v. 29 (2) p. 153-162. CN: DNAL S592.7.A1S6 LA: English AB: The distance between "hot spots" for N-mineralization (N-rich clover residues) and for N-immobilization (high C-to-N straw) in soil was experimentally manipulated to investigate its effect on the competition between plant roots and microorganisms for mineralized N. The experiment demonstrated that plant roots were reasonably competitive, resulting in deprivation of the N-supply to the microorganisms growing on the straw material, but this was totally dependent on the distance between the N-rich and the N-poor sites in the soil. The critical distance was somewhere between 3 and 6 mm, above which plant roots outcompeted the microorganisms more or less completely. Our study illustrates an important mechanism by which plant roots can interfere with microbial N-transformations in soil. It may be the mechanism responsible for an often alleged "stimulation" of N-mineralization by plant roots. The mineralization rate of clover- and straw-C was measured in planted as well as unplanted soil. The presence of plant roots retarded the straw-C mineralization significantly, but not clover C. Record 7 of 14 - AGRICOLA 1992-1997 AU: Jackson,-R.B.; Caldwell,-M.M. TI: Integrating resource heterogeneity and plant plasticity: modelling nitrate and phosphate uptake in a patchy soil environment. SO: J-ecol. Oxford : Blackwell Science Ltd. 1996. v. 84 (6) p. 891-903. CN: DNAL 450-J829 LA: English AB: We used the Barber-Cushman model of nutrient uptake to simulate the importance of soil heterogeneity and root plasticity for nitrate (NO3(-)) and phosphate (P) uptake Model inputs included root physiological parameters and soil characteristics obtained from five years of field studies in the sagebrush steppe. At an intensively sampled field site the average variation in soil P and NO3(-) around individual plants was 3-fold and 12-fold (3 X and 12 X, respectively), the range of soil variability used in our simulations. In soil patches three-fold enriched in P (3 X), simulated P uptake was three to four times greater than in soil of background P concentrations (1 X). The importance of soil heterogeneity and root plasticity was even more pronounced for NO3(-). In 12 X soil patches, NO3(-) uptake was 7-20 times greater than at 1 X, depending on simulation conditions. Plasticity (root proliferation and increased uptake kinetics) accounted for up to 75% of NO3(-) and over 50% of P acquired from enriched soil patches. Even without plasticity, nutrient uptake increased substantially in enriched patches because of higher soil-solution concentrations. Using the same model we simulated P and NO3(-) uptake for an actual 0.25-m2 soil area in the field. Plant acquisition of P in this area was 28% higher with root plasticity than without, equally attributable to root proliferation and increased uptake kinetics. Plant NO3(-) uptake was 61% greater with plasticity, due almost exclusively to increased uptake capacity of roots. We also simulated P and NO3(-) uptake in hypothetical soil arrays containing an equivalent quantity of nutrient distributed homogeneously or heterogeneously. A plant without plasticity always. acquired less P or NO3(-) in the heterogeneous arrays than in the homogeneous arrays. With plasticity, it acquired more nutrients in three of four cases compared to the homogeneous 'control'. We present these simulations as a way to integrate field experiments, generate and test hypotheses, and stimulate discussion. Given that heterogeneity is the norm rather than the extreme. our simulations highlight the importance of soil heterogeneity and root plasticity for both nutrient acquisition and plant competition in the field. Record 8 of 14 - AGRICOLA 1992-1997 AU: Roy,-S.; Singh,-J.S. TI: Seasonal and spatial dynamics of plant-available N and P pools and N-mineralization in relation to fine roots in a dry tropical forest habitat. SO: Soil-biol-biochem. Exeter : Elsevier Science Ltd. Jan 1995. v. 27 (1) p. 33-40. CN: DNAL S592.7.A1S6 LA: English AB: Seasonal dynamics of mineral N (NH4+ and NO3-), available P (NaHCO3-Pi) and N-mineralization rates in patchy and adjacent microsites Of a dry tropical forest were examined in relation to fine root biomass. Patchy microsites were richer in mineral N and P. Year-long averages indicated that NH4+ dominated over NO3- in the nutrient rich patchy microsites where fine root biomass, production and turnover were comparatively greater than in the nutrient-poor adjacent microsites which were dominated by NO3-. However, during the wet season nitrate was the dominating form of mineral-N in all the microsites. N-mineralization was higher in the patchy microsites than in the adjacent microsites. Fine root biomass was positively correlated with the N-mineralization and nitrification rates in nutrient-rich microsites indicating that fine root development was facilitated by higher amounts of mineral-N irrespective of the form in which N was prevalent. Record 9 of 14 - AGRICOLA 1992-1997 AU: Roy,-S.; Singh,-J.S. TI: Consequences of habitat heterogeneity for availability of nutrients in a dry tropical forest. SO: J-ecol. Oxford : Blackwell Scientific Publ., 1913-. 1994. v. 82 (3) p. 503-509. CN: DNAL 450-J829 LA: English AB: 1. This study evaluates the consequences of habitat heterogeneity in terms of patchy availability of nutrients in a dry tropical forest. The forest floor was characterized by the presence of topographic depressions; litter accumulation in these troughs gives rise to patchy microsites which are different in appearance from the adjoining non-patchy milieu (flats). 2. Litter mass and decomposition were significantly greater in the troughs than in the flats. Decomposition of 95% of the leaf litter needed 488 days in the troughs compared to 576 days in the flats. 3. Troughs were characterized by higher levels of microbial biomass and available nutrient pool. N-mineralization rates were also higher in the troughs. C, N and P concentrations in microbial biomass were positively correlated with N-mineralization rate when data for flats and troughs were pooled. The study indicated that immobilization and release of nutrients occurred in different parts of the year. 4. Fine roots were concentrated in the troughs with the net fine root production of 488 g m-2 year-1 compared to 218 g m-2 year-1 in the flats. Fine root biomass was positively correlated with the concentrations of mineral N and available P in the troughs. N-mineralization explained 46-63% variability in fine root biomass in the microsites. 5. The troughs supported greater herbaceous shoot biomass, particularly in the rainy season, thus preventing leaching by immobilizing excess nutrients. Herbaceous shoot biomass was positively correlated with N-mineralization and mineral N throughout the growing season and across the fertility gradient. 6. Troughs, which accumulated litter and trapped the nutrients in the dynamic microbial biomass, were. characterized by higher amounts of organic C, total and mineral N, available P and nutrient supply potential. These areas attracted fine roots to support tree growth, compensated for nutrient limitation and sustained a fairly high level of net primary production in otherwise nutrient poor, leached, impoverished and shallow soil milieu. Record 10 of 14 - AGRICOLA 1992-1997 AU: Pregitzer,-K.S.; Hendrick,-R.L.; Fogel,-R. TI: The demography of fine roots in response to patches of water and nitrogen. SO: New-phytol. Cambridge : Cambridge University Press. Nov 1993. v. 125 (3) p. 575-580. CN: DNAL 450-N42 LA: English Record 11 of 14 - AGRICOLA 1992-1997 AU: Bolton,-R.G.; Boddy,-L. TI: Characterization of the spatial aspects of foraging mycelial cord systems using fractal geometry. SO: Mycol-Res. Cambridge : Cambridge University Press. June 1993. v. 97 (pt.6) p. 762-768. CN: DNAL QK600.M82 LA: English Record 12 of 14 - AGRICOLA 1992-1997 AU: Wiren,-M.-von; Romheld,-V.; Morel,-J.L.; Guckert,-A.; Marschner,-H. TI: Influence of microorganisms on iron acquisition in maize. SO: Soil-Biol-Biochem. Exeter : Pergamon Press. Mar 1993. v. 25 (3) p. 371-376. CN: DNAL S592.7.A1S6 LA: English AB: Graminaceous species can enhance acquisition of iron (Fe) by release of phytosiderophores mainly from apical root zones. However, phytosiderophores are readily degradable by microorganisms. To study the effect of rhizosphere microorganisms in Fe acquisition, maize plants were grown axenically or inoculated with a mixture of microorganisms in a limestone substrate supplemented with a small amount of Fe(III)-oxide. Axenic plants grew well without Fe deficiency symptoms and released considerable amounts of phytosiderophores. In contrast, inoculated plants showed severe symptoms of Fe deficiency chlorosis and much less phytosiderophores were detectable in the substrate. The severity of Fe deficiency chlorosis was strongly influenced by the mode of water supply either continuously by glass fibre wicks or by periodic short-term flooding. Inoculated plants became more chlorotic, when watered by flooding than plants watered by glass fibre wicks. This was suggested to be due to greater microbial degradation of phytosiderophores as a consequence of higher microbial population density in apical root zones, the sites of phytosiderophore release. To prove this hypothesis maize plants were grown in a silty loam soil. Short-term periodic flooding resulted in a uniform distribution pattern of rhizosphere microorganisms along the root axis, whereas in non-flooded plants the number of rhizosphere microorganisms was lower in apical root zones and increased sharply from 0-20 to 20-40 mm distance from the root apex. It is concluded, that in solid substrates a low population density of rhizosphere microorganisms in the apical root zone is of particular importance for efficient Fe acquisition by phytosiderophores in graminaceous species like maize. Record 13 of 14 - AGRICOLA 1992-1997 AU: Bowman,-R.A.; Savory,-D.J. TI: Phosphorus disribution in calcareous soil profiles of the Central Plains. SO: Soil-Sci-Soc-Am-J. Madison, Wis. : The Society. Mar/Apr 1992. v. 56 (2) p. 423-426. CN: DNAL 56.9-SO3 LA: English AB: Deep-rooted crops benefit from high subsurface P content. While some documentation exists for high levels of available inorganic P well below the soil solum, very little information exists on organic-P contents deep in the soil profile. This research was conducted to document the presence of large pools of available organic and inorganic P on top of a carbonate layer 2.2 m below the soil surface. Additionally, soil organic C, N, texture, and selected mineral concentrations were determined to assess their correlations with total P. Soil samples (Aridic Argiustolls) from two fields that have been out of cultivation for at least 10 yr were taken in 0.15-m increments to a depth of approximately 2.5 m. The surface soils (0.0-0.3 m) were high in nutrients (11.0 g C and 1.1 g N/kg soil) and negligible in carbonates; the middle soil layers (0.30-0.25 m) were low in nutrients (4.0 g C and 0.3 g N/kg) and intermediate in carbonates (90 g/kg); and the deep soil layers (2.25-2.55 m) were high in available inorganic and total organic P, and very high in carbonates (> 300 g/kg). The total P concentration in the profile was inversely correlated with the percentages of sand and Ca, and directly correlated with the total content of Fe and Al. Total organic C and N and, to a greater extent, total organic P accumulated near or on top of a carbonate layer. Most of the organic C and P below 0.45 m were soluble in 2 M HCl. For the surface soil (0.0-0.45 m), the bulk of the organic P was extracted only after 2 M HCl pretreatment. Alfalfa and similar deep-rooted crops may benefit from this large reserve of available P near the water table. Record 14 of 14 - AGRICOLA 1992-1997 AU: Escamilla,-J.A.; Comerford,-N.B.; Neary,-D.G. TI: Spatial pattern of slash pine roots and its effect on nutrient uptake. SO: Soil-Sci-Soc-Am-J. Madison, Wis. : The Society. Nov/Dec 1991. v. 55 (6) p. 1716-1722. CN: DNAL 56.9-SO3 LA: English AB: Nutrient-uptake models generally assume that roots are uniformly arrayed throughout a soil volume. In high-fertility soils, departure from this regular distribution is not thought to affect nutrient-uptake predictions if the roots are randomly arranged, but has the potential to dramatically change nutrient-uptake predictions if roots are clumped. This study was conducted to document root spatial patterns in a forest ecosystem and to determine if spatial patterns affect how we conceptualize nutrient uptake in low-fertility soils. Roots were mapped on horizontal faces at 2-cm depth intervals. Spatial patterns were measured using variance/mean ratio and nearest neighbor distance (R) indices. The spatial pattern of slash pine (Pinus elliottii Engelm.) roots, using either variance/mean or R index, was random and was not affected by either the understory plant community or planting microsite. However, 63% of the pine roots in the check plots were within 0 to 0.6 cm of another pine root, while a similar percentage of pine roots was within 0 to 1.0 cm of another pine root in the weed-controlled area. At these interroot distances, little interroot competition for K was expected. In contrast, virtually all roots had P-uptake efficiency of < 30%, regardless of understory competition. When nutrient-uptake efficiency is a function of interroot distance for a random root population in low-fertility soils, average interroot distance cannot be considered typical of the root population.