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Subsurface banding of P fertilizer is more effective than broadcast and incorporation for annual crops on P-deficient sites. Subsurface banding in established alfalfa (Medicago sativa L.) may damage plants. This study compared spring-applied, broadcast dry monoammonium phosphate (MAP) and fluid ammonium polyphosphate (APP), and APP applied in surface bands with 15-, 30-, or 60-cm spacing, at rates equivalent to 0.5x and lx the soil test recommendation for yield, tissue P concentration, and P uptake at six sites. There was no difference in soil test P measured after the first cutting between broadcast MAP or APP. Yield responses to P occurred at all sites and ranged from a low of 0.7 Mg [ha.sup.-1] (7%) averaged across P rate, to 2.6 Mg [ha.sup.-1] (46%) at the 0.5x rate and 5.4 Mg [ha.sup.-1] (95%) at the lx rate above the 0 kg P [ha.sup.-1] treatment. Yield was higher with MAP than with APP for five of 19 individual harvests, while total yield was 1.0 Mg [ha.sup.-1] higher with MAP than with APP at one site-year. Phosphorus source effects on P concentration and uptake were similar to those on dry matter yield. There was a linear decrease in yield with increasing band spacing for one site-year and a quadratic response for another. Responses to band spacing in tissue P concentration for nine harvests suggest that band spacing of 15 and 30 cm may enhance P availability relative to broadcast or 60-cm spacing. In only one site-year did we find a yield advantage of MAP over APE or of surface band over broadcast APP. Abbreviations: MAE monoammonium phosphate; APE ammonium polyphosphate.

Root growth responses to separately placed of bands of N and P fertiliser were examined at the 3-leaf(GS13) and stem extension growth stages (GS30) for wheat (Triticum aestivum L. cv. Yitpi) growing in 2 major alkaline soil types from the rainfed (375-420 mm) grain production regions of south-eastern Australia. Intact cores of a Sodosol and a Vertosol were destructively sampled and changes in root length density (RLD) and root diameter distribution within the soil profile were examined using restricted maximum likelihood analysis and principal component analysis, respectively. At GS13, RLD increased in the Vertosol when only P was applied, although there was no shoot growth response. The root response to P consisted of a spatially generalised increase in RLD, rather than a specific increase in the vicinity of the P fertiliser band. There was a substantially greater, but still generalised, increase in RLD in the Vertosol when both N and P fertiliser were applied, although there was no response to N fertiliser (without P). The distribution of root length in diameter classes changed with depth in the profile at GS13 but was otherwise similar, regardless of soil types and fertiliser treatment. The root responses to fertiliser at GS30 also consisted of a generalised proliferation of RLD in the topsoil, with no detectable fertiliser-specific changes in the location or structure of the root system. Shoot and root growth increased to a similar level at GS30 when plants were supplied with N, irrespective of P, and root diameter distributions were again insensitive to fertiliser treatment. Plants responded to N by increasing the RLD of relatively fine roots (100-250 µm), which was a P style of acquisition strategy that was possibly triggered by moisture limitations. Consequently, the root responses to fertiliser under realistic semi-arid conditions did not follow expectations based on nutrient acquisition studies. Instead, wheat plants responded to N or P fertiliser with a generalised proliferation of fine roots, apparently to better compete for finite water and nutrients., Introduction Root systems are of fundamental importance to crop productivity because they acquire the water and nutrients that support shoot growth. Unfortunately, root systems and root function are difficult to [...]

Phosphorus fertilization of St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze] is performed on the basis of soil tests designed for agronomic crops. The objectives of this study were to determine the critical minimum P application rate and soil and tissue P concentration of S. Augustinegrass grown in sandy soils. Three studies were conducted in a glasshouse using a Pomona sand, two Tavares sands, and a Pottsburg sand. Established pots of 'Floratam' St. Augustinegrass received P at 0, 0.14, 0.27, 0.54, and 1.09 g [m.sup.-2] every four weeks for 16 weeks for Study 1 and 12 weeks for Studies 2 and 3. Critical minimum tissue P concentration was determined to b 1.8 g [kg.sup.-1] on dry weight basis. Minimum P application rate was 0.14 g [m.sup.-2] [4-wk.sup.-1] to obtain acceptable turfgrass quality and growth rate. Additional growth was not observed when Mehlich-1 P level was greater than 7, 8, 9, and 5 mg [kg.sup.-1] for Pomona sand, Tavares sand (a), Pottsburg sand, and Tavares sand (b), respectively. Phosphorus fertilization would not be recommended if soil Mehlich-1 P concentration is above 10 mg [kg.sup-1] for sandy soils or tissue P level is beyond 1.8 g [kg.sup.-1] on dry weight basis. Phophorus application of 0.14 g [m.sup.-2] 4-[wk.sup.-1] is recommended when P is required.

Shortened fallows have reduced the productivity of traditional upland rice (Oryza sativa L.)-based slash-and-burn systems in northern Laos. New cultivars and management methods are needed for food security in the region. To assess their potential for increasing upland rice productivity, this study compared two improved and three traditional upland rice cultivars in three fertilizer treatments: no fertilizer, nitrogen (90 kg N/ha), and N plus phosphate (50 kg P/ha), in six trials over 2 yr. The two improved cultivars had consistently higher grain yields than the traditional cultivars across all fertilizer treatments (3.9 vs. 2.1 t/ha). The improved cultivars had greater total biomass and harvest index, more panicles, and were shorter than the traditional cultivars. They were also more responsive to N without applied P than traditional cultivars. Two of three traditional cultivars gave a response that was similar to the improved cultivars when both N and P were applied. In addition, on-farm trials were conducted at 13 locations to compare the productivity of the improved cultivars with fertilizer (N-P-K 60-26-50 kg/ha) to farmers' practice consisting of traditional cultivars without fertilizer. In these trials, the improved cultivars with fertilizer achieved much higher grain yields than farmers' practice (3.0 vs. 1.8 t/ha). Improved cultivars and moderate inorganic fertilizer application offer a new approach to increasing the productivity of upland rice in Laos.

Recent field trials on alkaline soils in southern Australia showed significant grain yield responses to liquid compared with traditional granular forms of P fertiliser. However the advantages of liquid over granular P forms of fertiliser has not been consistent on all soil types. In order to better predict the soil types on which liquid P fertilisers are likely to have potential, a glasshouse trial was conducted to compare the responsiveness of wheat to both liquid and granular forms of P on a wide range of Australian soils. A granular P fertiliser (triple superphosphate) and 2 liquid fertilisers (phosphoric acid and ammonium polyphosphate) were compared at a rate equivalent to 12 kg P/ha in 29 soils representing many of the soil types used for grain production in Victoria and South Australia. Wheat biomass was enhanced by P application in 86% of the soils tested. In 62% of the P-responsive soils, wheat dry matter was significantly greater when liquid P fertilisers were used compared with the granular form. Chemical analysis of the soils tested showed that the better performance of liquid P forms was not correlated to total P concentration in soil, P buffer capacity, or P availability as measured by Colwell-P. However, there was a significant positive relationship between calcium carbonate (CaC[O.sub.3]) content of soil and wheat responsiveness to liquid P fertiliser. Additional keywords: liquid fertilisers, fluid fertilisers, phosphorus, alkaline soils, wheat., Introduction Phosphorus is the most expensive major nutrient used in broadacre cropping in Australia, with the cost of P fertiliser to Australian farmers being approximately $1.645 billion per year (FIFA [...]

Phosphate sorption curves were measured for 103 Western Australian soils sampled from farmers' fields. A measure of phosphate buffering obtained from a fitted curve was compared with indexes obtained from single-point measurements of phosphate sorption. The single-point indexes were adjusted for the phosphate present in the sampled soils by adding the phosphate extracted by the bicarbonate reagent to the measured sorption. Iron and aluminium extracted by an oxalate solution were measured as indirect indexes. The single-point indexes were closely correlated with the values obtained from the sorption curve. Their correlation was much larger than that of indirect measures. Additional keywords: phosphate, adsorption isotherm, sorption indexes., Introduction Although the buffering capacity of a soil for phosphate has a large effect on optimum phosphate fertiliser rates, analytical laboratories are reluctant to measure sorption curves. They argue that [...]

Sugarcane (Saccharum spp.) in Florida is principally grown on Histosols in the Everglades Agricultural Area. Soil-test-based P fertilization recommendations have not been addressed since the 1970s. The objectives of this research were to evaluate the most acceptable soil test P extractant that best correlates to crop yield, and to define soil test P groupings associated with crop response to applied P. Results will be used in the future to recalibrate soil test data to yield and rate of P application. Phosphorus trials were conducted at four sites on organic soils between 1968 and 1972 and additionally at eight sites on organic soils between 1982 and 1990. Phosphorus applications ranging from 0 to 98 kg P [ha.sup.-1] were broadcast or row-applied in combination with different cultivars, and/or K, Si, or S rates at 12 sites (multiple experiments used per site per crop). The effectiveness of water, acetic acid, and Mehlich-1 extractable soil P as yield response predictors was determined. Acetic acid extractable P was more highly correlated to sugar and cane yields (r = 0.72* and 0.63**, respectively) than water-extractable P (r = 0.27** and 0.39**, respectively). Mehlich-1 extractable P was poorly correlated to sugar (r = 0.25*) and cane (r = [0.05.ns) yields. Acetic acid extractable P was selected as the best-suited extractant related to crop yield response to P fertilization. Soil test calibration curves (i.e., relative yield as a function of acetic acid extractable P) were determined from the choice of seven types of regression models, in which the reciprocal function was chosen with the highest coefficient of determination (R2) and minimized residuals. Soil acetic acid extractable P criteria were developed to define soil test level groups associated with yield response conditions: low soil test levels ranged from 0 to 9 mg [L.sup.-1], medium from 9 to 39 mg [L.sup.-1], and high exceeded 39 mg P [L.sup.-1].

A study of Seathwaite tarn, a reservoir in the Lake District, UK, shows that the addition of phosphate fertilizers increases the pH and primary productivity of lakes with low pH of water. Primary production by phytoplankton increases the assimilation of nitrate which makes the lake water basic. The addition of phosphate treatment does not influence the community structure of the lakes significantly. This treatment is most effective if the residence time of the lake is more than one year, the initial pH of water is mildly acidic, and additional nitrate gets in from the atmosphere or catchment.

Abstract This paper reviews phosphorus loss from productive high rainfall grazing systems. In particular it describes the processes occurring when phosphatic fertilisers are added to soil, the different pathways through [...]

Just as we were facing up to peak oil--the maximum in the rate of global oil production that is imminent or (by some estimates) has just passed--we have another peak [...]

Too much of a good thing can often be a waste--or even a downright pollutant--but not when it's unused phosphorus fertilizer. Wheat, barley, corn, and other major crops require phosphorus [...]