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Catalogue: GRDC Updates
In the northern grains region P is commonly the next limiting nutrient after N; an adequate supply is vital to ensure N is used efficiently... Given that sorghum is generally a dominant crop in many rotations in the east of the Northern Grains Region and a significant secondary crop in most other areas, it is of significance to recognise that the recent research evidence for increasing the replacement/ maintenance rates for sorghum based on the research from Lester et al. indicating that the commonly used removal figure of 2.3 kg P/tonne (0.23 % P in grain) quoted in the NLWRA 2001 is probably too low for local condition... More recent studies have indicated that 3.7 kg P/tonne (0.37 % P in grain) is more realistic for modern varieties grown on the soils of the vertosols of the Darling Downs and Nthn NSW. Combining higher unit removal and high yield per unit of soil moisture makes sorghum the most influential determinant of soil P status in many areas and a key factor in soil P decline even where replacement rates are targeted...
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Catalogue: GRDC Updates
Partial P budgets (P applied minus P removed in harvested product) are generally negative across the northern grains region indicating that soil P reserves are being used to support crop growth, but the uncertainty in prediction of crop P requirements from pre-plant soil tests has been highlighted by the results obtained from numerous P rate field experiments undertaken in GRDC project DAQ00084... To assess the availability of this acid extractable P, iron oxide strips were used as 'sinks' to continuously remove P from the soil solution forcing P desorption and dissolution of P compounds to replenish soil solution P. Figure 2 indicates that the acid extractable fraction was a major contributor of P to the soil solution and is potentially available to crops... Field experiments have confirmed the unreliability of Colwell-P for discriminating P-responsive from P-adequate sites, even if the Colwell-P status of the sub-surface is considered as being more representative than the 0-10 cm layer of the soil being exploited by the crop roots...
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Catalogue: GRDC Updates
New ways to estimate crop needs and deliver P to improve the return on fertiliser investment.. The implications of this from a productivity perspective are unclear, but early results are suggesting that some significant yield gains may be possible on these soils... While the results suggest that once soils have become depleted in subsoil P significant yield gains can be achieved by improving soil P status, there are a large number of practical issues that need to be resolved...
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Catalogue: GRDC Updates
Toward a Better P Nutrition Package: Diagnosing P Status and Application Strategies to Improve Fertiliser Response.. Preliminary results suggest that once subsoil P becomes limiting, yield losses can become substantial and major changes to P application strategies will be needed... Surplus or deficit was calculated from P inputs in fertilizer minus P removed in grain...
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Catalogue: GRDC Updates
Phil Moody will talk more about Colwell/BSES-P dynamics and crop response in small volumes of soil... Since Colwell-P is still useful in predicting plant available P, poor fertiliser response could be attributed to other limitations on yield such as climate, other nutritional constraints, or the differences in P mineralogy that is measured by BSES-P and their release rate... Dr. Chris Guppy < Keep browsing 0 Responses to Using Colwell and BSES extractable phosphorus to predict Faba bean (Vicia faba L.) response..
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Catalogue: GRDC Updates
We first determined (1) the amount of P applied as fertilisers to crops in WA and (2) the amount of P removed in harvested grains by multiplying grain yield by the P content of the grains... For example, if we removed 5 kg P/ha in the form of P contained in grains and we applied 10 kg P/ha as fertiliser, then the P balance efficiency is 5/10x100 = 50 %. P balance efficiency allows us to assess along with soil test P data if we are building-up, maintaining or depleting soil P... We estimate that about 87% of the wheat paddock soil samples examined are no longer P deficient (exceed their critical values)...
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Catalogue: GRDC Updates
The interpretation of the values generated from those soil tests has remained a dark art and this short paper hopes to summarise 'where we are at' with the principles we use to interpret all those soil tests that have been increasingly adopted by industrious agronomists and producers... Considerably more work is required to improve the precision of these critical values, and to understand the mechanism behind the increase in those values where soil Na or Mg status is high... We have been working on a method to estimate the reserves of K available in each soil and the results of this research have been presented in previous Updates...
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Catalogue: GRDC Updates
The experiments are run over 4 years to test the water use efficiency, productivity and riskiness of: (i) a range of continuous cereal systems and the decisions around inputs, timing and agronomy; and (ii) potential break crop systems; across soils of differing potentials... Comparison with the non N-limiting yield potential estimated using the APSIM model of 5.05 t/ha in the swale, 6.06 t/ha in the mid-slope and 5.12 t/ha in the dune, suggests the actual yields are very close to potential yield in the wheat following pasture in the swale but well below for all treatments in the dune and mid-slope (Figure 3)... A build-up of fertility in the swale where fertilizer applications have been uniform across soil types in the past and the swales have under-performed in the dry years has meant that N was not limiting in this soil type and potential yield was attainable in the wheat following pasture where a disease break had been provided...
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Catalogue: GRDC Updates
Increasing the soil organic matter content of soils takes time and requires higher levels of carbon inputs and reduced levels of carbon outputs... The research undertaken by Clive Kirkby (CSIRO) and farmer demonstration projects are investigating management practices which can result in an increase in the humus fraction of the total SOM pool... Soil with Carbon increase of 0.8% had the lowest increase for lowest probability at approximately 4000kg/ha...
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Catalogue: GRDC Updates
Mitscherlich equation is currently used to define the Colwell-P soil test - crop response relations for crop species, soil type and seasonal combinations... The paper presents an alternative equation to defining Colwell-P soil test critical levels for wheat which overcomes this problem and will result in a more profitable and environmental sustainable wheat production system... Where, RY is relative yield; a, b, and c are constants; and Colwell-P is soil P measured for the 0-10 cm layer by the procedure of Colwell (1963)...
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