Effect of phosphorus fertiliser on the yield of potato tubers (Solanum tuberosum L.) and the prediction of tuber yield response by soil analysis

1989 ◽  
Vol 29 (3) ◽  
pp. 419 ◽  
Author(s):  
NA Maier ◽  
KA Potocky-Pacay ◽  
JM Jacka ◽  
CMJ Williams
Keyword(s):  
Total Phosphorus ◽  
Tuber Yield ◽  
Soil Phosphorus ◽  
Total Yield ◽  
Maximum Yield ◽  
Critical Values ◽  
Yield Response ◽  
Soil Test ◽  
Phosphorus Extraction ◽  
Bray 1

Field experiments were conducted over 6 years at 33 sites throughout the main potato growing areas of South Australia to examine the effects of applied phosphorus (banded at planting), at rates up to 300 kg/ha, on the total yield and size distribution of tubers and to calibrate, in terms of total yield, 8 soil phosphorus extraction procedures (Colwell, Olsen, Bray 1, Bray 2, Mehlich no. 1, lactate, fluoride and total). Phosphorus application significantly (P< 0.05) increased total tuber yield at 16 sites. The mean relative yield for these responsive sites was 69.7% (range 37.4- 91.2%) compared with 97.5% (range 88.0-102.5%) for the non-responsive sites. Tuber size distributions were determined at 13 sites and, depending on site and cultivar, the yield of 80-450 g tubers for the highest yielding treatments represented from 64.2 to 93.7% of the total yield of tubers for those treatments. For each soil phosphorus extraction procedure the Mitscherlich and Smith-Dolby bent-hyperbola models and the Cate-Nelson separation were used to investigate the correlations between yield response and extractable and total phosphorus in the surface (0- 15 cm) soil samples and to calculate critical values. For loamy sand to sandy clay loam surface soils, the order of efficacy of soil tests based on the coefficients of determination (r2) calculated using the Mitscherlich and Smith-Dolby bent-hyperbola models was Bray 1 and Bray 2 > Olsen > lactate, Mehlich no. 1, fluoride and Colwell. The coefficients of determination ranged from 0.88 (Bray 1) to 0.64 (Colwell) for the Smith-Dolby bent-hyperbola model and from 0.86 (Bray 1) to 0.65 (fluoride) for the Mitscherlich model. Yield response was not correlated with total phosphorus concentration. Using the Smith-Dolby benthyperbola model the critical phosphorus values (s.e. in parentheses) were: 25.8(1.8), 40.9(2.6), l6.8(1.4), 13.9(1.0), 38.4(3.1), 24.2(2.9) and 35.1(3.0) mg/kg for the Bray 1, Bray 2, Olsen, lactate, fluoride, Mehlich no. 1 and Colwell methods, respectively. Yield deficits >20% were associated with phosphorus soil test values t 2 0 mg/kg (Bray 1 method) and P-sorption values >240 mg/kg. Rates of 48-73 kg P/ha banded at planting were required for 95% of maximum yield at the deficient sites. For acid coarse-grain sand surface soils, significant Cate-Nelson separations were obtained for the Colwell, Bray 1, Bray 2, Mehlich no. 1 and fluoride methods, the critical phosphorus values were 7.5, 7.0, 5.5, 6.5 and 8.0 mg/kg, respectively. The order of efficacy of the soil tests was Bray 2 (r2 = 0.66) >Bray 1, Colwell, Mehlich no. 1 and fluoride (all r2 = 0.55). Yield deficits >10% were associated with soil test values t 6 mg/kg (Bray 1 method). Rates of 27-59 kg P/ha banded at planting were required for 95% of maximum yield at the deficient sites. Data are presented which suggest that for similar soil types and extraction procedures critical values or critical concentration ranges may apply across a range of growing conditions, planting times and cultivars.

Using soil testing and petiole analysis to determine phosphorus fertiliser requirements of potatoes (Solanum tuberosum L. cv. Delaware) in the Manjimup-Pemberton region of Western Australia

2000 ◽  
Vol 40 (1) ◽  
pp. 107 ◽  
Author(s):  
M. A. Hegney ◽  
I. R. McPharlin ◽  
R. C. Jeffery
Keyword(s):  
Solanum Tuberosum ◽  
Tuber Yield ◽  
Solanum Tuberosum L ◽  
Maximum Yield ◽  
Soil Testing ◽  
Yield Response ◽  
Soil Test ◽  
Versus Level ◽  
Soil Test P ◽  
The Relationship

Field experiments were conducted over 3 years at 21 sites of varying phosphorus (P) fertiliser histories (Colwell P range: 9–170 g/g) in the Manjimup–Pemberton region of Western Australia to examine the effects of freshly applied (current) and previously applied (residual or soil test ) P on the yield of potatoes (Solanum tuberosum L. cv. Delaware). Phosphorus was placed (banded) at planting, 5 cm either side of and below seed planted at 20 cm depth, at levels up to 800 kg P/ha. Exponential [y = a – b exp (–cx)] regressions were fitted to the relationship between tuber yield and level of applied P at all sites. Weighted (according to the variance) exponential regressions were fitted to the relationship between yield responsiveness (b/a, from the yield versus level of applied P relationship) and Colwell P, and two P sorption indices—phosphate adsorption (P-adsorb) and a modified phosphate retention index (PRI(100)). A weighted exponential regression was also fitted to the relationship between the level of applied P required for 95% of maximum yield (Popt; also from yield versus level of applied P) and P-adsorb and PRI(100). A weighted linear regression best described the relationship between Popt and Colwell P. Phosphorus application significantly (P<0.10; from the regression analysis) increased total tuber yield at all but 4 sites. Marketable tuber yield response paralleled total tuber yield response at all sites and averaged 85% of total yields (range 63–94%). Colwell P gave a good prediction of the likely yield response of potatoes across all sites. For example, the yield responsiveness (b/a) of potatoes in relation to Colwell P decreased exponentially from 1.07 at 0 g/g to 0, or no yield response, at 157 g/g Colwell P (R2 = 0.96) i.e. the critical Colwell P for 95% of maximum yield of potatoes on soils in the Manjimup–Pemberton region. Similarly, no yield response (b/a = 0) would be expected at a P-adsorb of 180 g/g (R2 = 0.69) or a PRI(100) of 46 (R2 = 0.61). The level of applied P required for 95% of maximum yield (Popt) decreased linearly from 124 kg/ha on infertile sites (<5 g/g Colwell P) to 0 kg P/ha at 160 g/g Colwell P (R2 = 0.66). However, a more accurate prediction of Popt was possible using either P-adsorb or PRI(100). For example, Popt increased exponentially from 0 kg/ha at <181 g/g P-adsorb (high P soils) to 153 kg/ha at a P-adsorb of 950 g/g (low P soils) (R2 = 0.75) and exponentially from 0 kg/ha at a PRI(100) of <48 (high P soils) to 147 kg/ha at a PRI(100) of 750 (low P soils) (R2 = 0.80). PRI(100) is preferred as a soil test to predict Popt for potatoes in the Manjimup–Pemberton region because of its superior accuracy to the Colwell test. It is also preferred to P-adsorb because of both superior accuracy and lower cost as it is a simpler and less time consuming procedure — features which are important for adoption by commercial soil testing services. A multiple regression including Colwell P, P-adsorb and PRI(100) only improved the prediction of Popt slightly (R2 = 0.89) over PRI(100) alone. When tubers were 10 mm long, the total P in petioles of youngest fully expanded leaves which corresponded with 95% of maximum yield was 0.41% (dry weight basis). These results show that, while the Colwell soil P test is a useful predictor of the responsiveness of potato yield to applied P across a range of soils in the Manjimup–Pemberton region, consideration of both the soil test P value and the P sorption capacity of the soil, as determined here by PRI(100), is required for accurate predictions of the level of P fertiliser required to achieve maximum yields on individual sites.

Response of winter-grown potatoes (Solanum tuberosum L.) to applied and residual phosphorus on a Karrakatta sand

1997 ◽  
Vol 37 (1) ◽  
pp. 131
Author(s):  
M. A. Hegney ◽  
I. R. McPharlin ◽  
R. C. Jeffery
Keyword(s):  
Solanum Tuberosum ◽  
Tuber Yield ◽  
Solanum Tuberosum L ◽  
Total Yield ◽  
Maximum Yield ◽  
Dry Weight ◽  
Phosphorus Recovery ◽  
Soil Test ◽  
Residual P ◽  
Soil Test P

Summary. The response of winter-grown potatoes (Solanum tuberosum L. cv. Delaware), as determined by yield, to applied (broadcast) phosphorus (P) (0–480 kg/ha) and to residual P was measured on an acutely P-deficient, newly cleared Karrakatta sand in experiments over 2 years. Tuber yield responded significantly (P<0.001) to level of applied P. Phosphorus at 162 kg/ha was necessary for 99% of maximum total yield, which corresponded to maximum economic yield. For 95% of maximum yield 99 kg/ha was necessary. Phosphorus recovery efficiency by tubers (P uptake by tubers/P applied, both in kg/ha) decreased from 0.14 at 30 kg P/ha to 0.04 at 480 kg P/ha. Bicarbonate-soluble P (soil test P) extracted from the top 15 cm of soil was determined on residual P sites in each experiment to which P was applied (as superphosphate) 9 months earlier at levels from 0 to 800 kg/ha. These soil test P levels were related (R2 = 0.91) to total tuber yield. The soil test P level required for 95% of maximum total yield was 33 g/g and for 99% was 51 µg/g. When tubers were 10 mm long, the total P in petioles of youngest fully expanded leaves which corresponded to 95% of maximum yield was 0.7% (dry weight basis), and for 99% was 0.87%. These results, while based on responses measured at 2 sites only, provide strong evidence that maximum yield of winter-grown potatoes on Karrakatta sands can be achieved with lower levels of P fertiliser than are currently used in commercial practice (125–300 kg P/ha). The results also show that soil testing can be used to improve the P management of potato crops grown on the sandy soils of the Swan coastal plain.

scholarly journals Growth and Yield Response to Fertilizer Application and Nutritive Quality of Huckleberry (Solanum scabrum Mill.) Varieties Cultivatedin the Mount Cameroon Region

2019 ◽  
pp. 1-12
Author(s):  
Mbah H. Agwa ◽  
Ndah R. Njoh ◽  
Egbe E. Andrew
Keyword(s):  
Crude Protein ◽  
Lateral Roots ◽  
Total Yield ◽  
Maximum Yield ◽  
Poultry Manure ◽  
Growth And Yield ◽  
Heat Extraction ◽  
Yield Response ◽  
Fertilizer Treatment ◽  
Carotene Content

This study evaluated the effects of fertilizer on growth, yield and the nutritive value of three varieties of huckleberry (“White stem”, “Bamenda” and “Foumbot”). The treatments were NPK (20:10:10) at levels 0, 100, 150, 200Kg/ha and 10 Mg/ha poultry manure and the experiment was a randomized complete block design with three replicates. The Kjeldahl procedure was used for crude protein determination. The lipid content was determined with the soxlet reflux heat extraction method. The ß-carotene content was determined using spectrophotometry. Results indicated that plants supplied with 200 Kg NPK/ha fertilizer treatment had the highest plant height (66 cm) and leaf number (242) in “White stem” and “Bamenda” varieties respectively and these were significantly different from the control (P = 0.05). Leaf area was highest in “Foumbot” variety (343.1 cm2). The longest tap root length and number of primary lateral roots were noted particularly in “White stem” control plants and this was significantly different (P = 0.05) from plants supplied with fertilizers. Plants supplied with 10 Mg/ha poultry manure recorded the highest total yield for “White stem” (44.83 Mg/ha) while plants supplied 200 Kg NPK/ha had maximum yield for the “Bamenda” and “Foumbot” varieties (36.96 and 31.84 Mg/ha respectively). The “White stem” variety had the highest crude protein (303.8 mg/100 g) and ß-carotene content (1.9 mg/100 g); “Bamenda” variety had the highest total lipid (8.15%), and crude fibre (14.15%) contents, while total ash was highest in “Foumbot” (16.54%). Appropriate fertilizer levels would considerably improve huckleberry yield as well as improve income of vegetable farmers.

Mineral nutrition of soybeans grown in the South Burnett region of south eastern Queensland. 2. Prediction of grain yield response to phosphorus with soil tests

1983 ◽  
Vol 23 (120) ◽  
pp. 38 ◽  
Author(s):  
PW Moody ◽  
GF Haydon ◽  
T Dickson
Keyword(s):  
Grain Yield ◽  
Buffer Capacity ◽  
Soil Phosphorus ◽  
Maximum Yield ◽  
Relative Yield ◽  
Yield Response ◽  
Phosphorus Concentration ◽  
The South ◽  
Equilibrium Phosphorus Concentration ◽  
Highly Correlated

Grain yield response of soybean (Glycine max cv. Bragg) to applied phosphorus was measured at 19 experimental sites in the South Burnett region. The soil phosphorus supply factors of quantity, intensity, buffer capacity and rate were estimated by various soil chemical tests, and relative yield [(yield at nil applied phosphorus/maximum yield) x 100] regressed against these tests. The equilibrium phosphorus concentration-the intensity measure-accounted for the greatest percentage variation in relative yield (80%) and at 90% maximum yield was 0.014 �g P/ml. Phosphorus extracted by 0.01 M CaCl2 was highly correlated with the equilibrium phosphorus concentration (r2=0.93) and accounted for 73% of the variation in relative yield. Soil levels of calcium chloride-extractable phosphorus were interpreted as follows: < 0.044 �g P/g, response to phosphorus probable; 0.044 �g P/g to 0.058 �g P/g, response uncertain; > 0.058 �g P/g, response unlikely

Effects of radioactive phosphate fertilizers on yield and phosphorus uptake by ryegrass in pot experiments on calcareous soils from Rothamsted

1957 ◽  
Vol 49 (2) ◽  
pp. 160-168 ◽  
Author(s):  
G. E. G. Mattingly
Keyword(s):  
Total Phosphorus ◽  
Soil Phosphorus ◽  
Farmyard Manure ◽  
Phosphorus Uptake ◽  
Calcareous Soils ◽  
Yield Response ◽  
Phosphate Fertilizers ◽  
Pot Experiments ◽  
History Of ◽  
The Difference

1. Two factorial pot experiments with ryegrass grown on calcareous soils from adjacent long-term experiments on Hoosfield, Rothamsted, are described. The effects of the method of application of phosphate, of the amounts of saP tested and of the level of phosphate applied are discussed with special reference to the manurial history of the soils.2. Yield and total phosphorus uptake by ryegrass were slightly greater in the early stages of growth when superphosphate was applied as a powder than when an equal amount of phosphate was applied in solution, but this effect disappeared in later cuts of grass. Total phosphorus uptake was not significantly altered by the levels of 32P tested, and yields were only significantly decreased at one sampling date in one experiment. Uptake of fertilizer phosphorus decreased and ‘A’ values increased, however, in both experiments at the higher rates of application of 32P.3. The addition of fertilizer phosphorus, as superphosphate or monocalcium phosphate, increased the uptake of soil phosphorus by ryegrass on all soils on which there was a yield response to phosphate. The recovery of fertilizer phosphorus, estimated radiochemically, was less, therefore, than the increase in phosphorus uptake by the crop on the soils on which there was a yield response to phosphate fertilizers.4. ‘A’ values were determined on all soils and were shown to be almost independent of two- and five-fold increases in the amount of labelled phosphate tested. ‘A’ values were related to the previous phosphate manuring of the soils and increased by about one-third of the difference in phosphate content on soils that had received heavy applications of superphosphate or farmyard manure over 50 years ago. The ‘A’ values of soils that had recently received superphosphate in the field decreased in 3 years by more than the amount of phosphate taken up by the crops. ‘A’ values of soils that received rock phosphate in the field were lower and did not decrease with time.

Potassium nutrition of irrigated potatoes in South Australia. I. Effect on tuber yield and the prediction of tuber yield response by soil analysis

1986 ◽  
Vol 26 (6) ◽  
pp. 717 ◽  
Author(s):  
NA Maier
Keyword(s):  
Cation Exchange ◽  
Potassium Chloride ◽  
Cation Exchange Capacity ◽  
Tuber Yield ◽  
Relative Yield ◽  
South Australia ◽  
Exchange Capacity ◽  
Potassium Sulfate ◽  
Yield Response ◽  
Soil Test

Field experiments were conducted over 4 years at 25 sites throughout the main potato-growing areas of South Australia to calibrate the 0.5M sodium bicarbonate extraction procedure as a soil test for potassium and to examine the responses of irrigated potatoes to rates up to 1280 kg/ha K applied as potassium sulfate or potassium chloride either banded at planting or side-dressed after emergence. Potassium application at planting increased yield (P < 0.05) at 10 sites. The mean percentage yield deficit was 21%. There were significant correlations between relative yield and clay and sand contents, cation exchange capacity and bicarbonate-extractable potassium concentration in 0-15-cm surface soil samples collected before potassium fertiliser was applied. Percentage silt and pH were not correlated with relative yield. The bicarbonate-extractable potassium soil test accounted for 70% of the variance in relative yield compared with only 27% for percentage clay and 22% for cation exchange capacity. The prognostic critical bicarbonate-extractable potassium concentrations were: 153 -t 12 mg/kg for the Smith-Dolby bent hyperbola model, 143 mg/kg for the Cate-Nelson separation, and 133 or 176 mg/kg for the Mitscherlich model (concentrations at relative yields of 90 and 95% respectively). Yield responses are likely when soil bicarbonate- extractable potassium concentrations are below 120 mg/kg (deficient range), uncertain between 12 1 and 200 mg/kg (marginal range) and unlikely above 200 mg/kg (non-responsive range). Banding potassium chloride at planting significantly reduced yield compared with potassium sulfate at 2 out of the 14 sites used. The yield reductions occurred with potassium rates of 160 kg/ha or higher. There were significant increases in yield with side-dressing compared with basal application, at 2 of 5 responsive sites using rates of 320 kg/ha K or higher. None of the side-dressing treatments reduced tuber yields below control yields.

Prince Edward Island growers can reduce soil phosphorus buildup while maintaining carrot crop yield

2006 ◽  
Vol 86 (Special Issue) ◽  
pp. 1401-1403 ◽  
Author(s):  
Kevin R Sanderson ◽  
J. Brian Sanderson
Keyword(s):  
Crop Yield ◽  
Daucus Carota ◽  
Prince Edward Island ◽  
Soil Phosphorus ◽  
Maximum Yield ◽  
Yield Response ◽  
Environmental Damage ◽  
Soil P ◽  
Daucus Carota L ◽  
P Fertilizer

Producers seek to manage the application of nutrients in a manner that maximizes economic crop returns; however, emphasis must now include sensitivity to environmental issues such as increasing soil phosphorus. To address this issue in carrot (Daucus carota L.) production, we studied the effect of soil-applied P fertilizers on yield and soil P content in Prince Edward Island. Six field studies over a 3-yr period evaluated the yield response of carrot on sandy to loamy sand Orthic Podzol soils. Treatments consisted of pre-plant broadcast applied P at 0, 33, 66, 99 or 132 kg ha-1 on sites where residual P levels ranged from 81 to 162 µg P g-1. When the total yield response of carrots to increasing P levels was fitted to a quadratic response curve, 110 kg P ha-1 was required to achieve maximum yield, but an application of as little as 22 kg P ha-1 resulted in 95% of maximum marketable yield. This reduced application rate resulted in a saving of 88 kg P ha-1 and slowed the buildup of soil P levels. Therefore, by applying more conservative amounts of P fertilizer carrot growers can maintain excellent crop yield while reducing the potential for environmental damage caused by the buildup of soil P. Key words: Orthic Podzol soil P, tissue P, fertilizer P, maximum yield, Daucus carota L.

Assessment of soil phosphorus tests for situations in Australia where reactive phosphate rock and water-soluble phosphorus fertilisers are used

1997 ◽  
Vol 37 (8) ◽  
pp. 1027 ◽  
Author(s):  
P. G. Simpson ◽  
M. J. McLaughlin ◽  
A. J. Weatherley ◽  
P. W. G. Sale ◽  
V. Hoy ◽  
...  
Keyword(s):  
Phosphate Rock ◽  
Soil Phosphorus ◽  
Subterranean Clover ◽  
Soil Test ◽  
Reactive Phosphate ◽  
Reactive Phosphate Rock ◽  
P Content ◽  
Soil Test P ◽  
The Relationship ◽  
Bray 1

Summary. A selection of commonly used soil phosphorus (P) tests, which included anion and cation exchange resin membranes, were compared in a glasshouse experiment using subterranean clover, and evaluated in the field at 19 sites from the National Reactive Phosphate Rock Project in 1993 and at 6 sites in 1995. The ability of the soil P tests to predict plant response was used to evaluate the tests. In the glasshouse experiment the resin test was less effective than the Bray 1 and Colwell tests in its ability to assess the level of plant-available P from the different fertiliser treatments. Seventy-one percent of the variation in total P content of the subterranean clover shoots was explained by resin-extractable P values, whereas the Colwell procedure accounted for 81% and the Bray 1 procedure accounted for 78%. Water and CaCl2 extracts were poor predictors of P content. In the field experiments all tests evaluated performed poorly in describing the relationship between soil test P and the level of P applied and relative yield and soil test P over a wide range of soil types and environments. The Bray 1 procedure performed best but the relationship was poor.

Determining the fertiliser phosphorus requirements of intensively grazed dairy pastures in south-western Australia with or without adequate nitrogen fertiliser

2007 ◽  
Vol 47 (7) ◽  
pp. 801 ◽  
Author(s):  
M. D. A. Bolland ◽  
I. F. Guthridge
Keyword(s):  
Western Australia ◽  
Field Experiments ◽  
Maximum Yield ◽  
Dairy Herd ◽  
Yield Response ◽  
Soil Test ◽  
Mineral N ◽  
P Leaching ◽  
The Many ◽  
Yield Responses

Fertiliser phosphorus (P) and, more recently, fertiliser nitrogen (N) are regularly applied to intensively grazed dairy pastures in south-western Australia. However, it is not known if applications of fertiliser N change pasture dry matter (DM) yield responses to applied fertiliser P. In three Western Australian field experiments (2000–04), six levels of P were applied to large plots with or without fertiliser N. The pastures were rotationally grazed. Grazing started when ryegrass plants had 2–3 leaves per tiller. Plots were grazed in common with the lactating dairy herd in the 6-h period between the morning and afternoon milking. A pasture DM yield response to applied N occurred for all harvests in all three experiments. For the two experiments on P deficient soil, pasture DM yield responses also occurred to applications of P. For some harvests when no fertiliser N was applied, probably because mineral N in soil was so small, there was a small, non-significant pasture DM response to applied P and the P × N interaction was highly significant (P < 0.001). However, for most harvests there was a significant pasture DM response to both applied N and P, and the P × N interaction was significant (P < 0.05–0.01), with the response to applied P, and maximum yield plateaus to applied P, being smaller when no N was applied. Despite this, for the significant pasture DM responses to applied P, the level of applied P required to produce 90% of the maximum pasture DM yield was mostly similar with or without applied N. Evidently for P deficient soils in the region, pasture DM responses to applied fertiliser P are smaller or may fail to occur unless fertiliser N is also applied. In a third experiment, where the soil had a high P status (i.e. more typical of most dairy farms in the region), there was only a pasture DM yield response to applied fertiliser N. We recommend that fertiliser P should not be applied to dairy pastures in the region until soil testing indicates likely deficiency, to avoid developing unproductive, unprofitable large surpluses of P in soil, and reduce the likelihood of P leaching and polluting water in the many drains and waterways in the region. For all three experiments, critical Colwell soil test P (a soil test value that was related to 90% of the maximum pasture DM yield), was similar for the two fertiliser N treatments.

Phosphorus requirements of winter-planted lettuce (Lactuca sativa L.) on a Karrakatta sand and the residual value of phosphate as determined by soil test

1996 ◽  
Vol 36 (7) ◽  
pp. 897 ◽  
Author(s):  
IR McPharlin ◽  
RC Jeffery ◽  
DH Pitman
Keyword(s):  
Lactuca Sativa ◽  
Maximum Yield ◽  
Relative Yield ◽  
Phosphorus Recovery ◽  
Yield Response ◽  
Soil Test ◽  
Recovery Efficiency ◽  
Lactuca Sativa L ◽  
Soil Test P ◽  
Whole Plants

The phosphorus (P) requirements of crisphead lettuce (Lactuca sativa L. cv. Oxley) was measured over 2 consecutive winter plantings using superphosphate that was freshly applied and applied 9 months before planting, at 0-600 kg/ha on a newly cleared Karrakatta sand of low natural P fertility. There was a significant (P<0.001) head yield response to level of applied P in both years. Phosphorus uptake by whole plants and plant shoots was related to level of applied P in Mitscherlich relationships (R2 = 0.88). Phosphorus recovery efficiency (fertiliser P uptake by shoots/P applied, both in kg/ha) by shoots decreased from 0.16 at 50 to 0.04 at 600 kg applied P/ha. Phosphorus recovery efficiency by whole plants (shoots plus roots) decreased from 0.18 at 50 to 0.05 at 600 kg P/ha. The level of freshly applied P required for either 95 or 99% of maximum relative yield over the 2 years (maximum yield, 86 t/ha) was 276 and 427 kg P/ha (Mitscherlich relationship, R2 = 0.95), respectively at <10 �g/g soil test P (newly cleared sites). The marketable yield was 82 and 95% of total yield at 276 and 427 kg P/ha respectively. Bicarbonate-soluble P extracted from the top 15 cm of soil was determined on residual P sites over 2 years where P was applied at 0-600 kg/ha. These soil test levels were related to head yield in a Mitscherlich relationship (R2 = 0.88). The critical soil test P values required for either 95 or 99% of maximum relative yield, over the 2 years, were 80 and 115 �g/g, respectively. Phosphorus in the wrapper leaf at early heading required for 95 or 99% of maximum yield was 0.59 � 0.03 and 0.61 � 0.03% (spline regression, R2 = 0.80), respectively. Soil and plant testing could be used to assist in reducing fertiliser costs, improving utilisation of freshly- and previously-applied fertiliser P by lettuce and reducing P losses to water systems on the Swan Coastal Plain in Western Australia.

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