Potassium Newsheet   Vol 1 Iss 2 : Winter 2002

This newsheet is supported by:

If you would like to inform others about a potassium nutrition issue or project contact the newsheet editor, Jonnie White.  Comments or feedback about any articles are also welcome.  Should you not wish to receive future editions of the newsheet please click here.

WA: Windrow effects highlight the need for K

In recent years, some West Australian crops have been displaying improved growth along the windrows of previous crops.  In extreme cases, the differences in grain yield between on- and off-windrow areas can be ten-fold or more.  The windrow effect provides an ideal diagnostic opportunity with adjacent 'good' and 'bad' areas.  Using this comparative approach, researchers with the Department of Agriculture have determined that the effect is primarily due to nutritional factors, commonly K deficiency, but also deficiency of other nutrients and pH effects.

Where K is the predominant factor, the windrow effect develops because K reserves in the residue of the previous crop are concentrated in the windrow and developing K deficiencies are exacerbated in off-windrow areas.  In strip trials, top-dressed K has been able to improve yields in both on- and off-windrow areas provided sufficient rain is received to move nutrient into the active root zone, and it also has a significant residual value for following crops.  For more information on the work undertaken by the Department of Agriculture contact Bill Bowden by email or on        (08) 9690 2190, or read the article on this topic available in the Research Library of the Potassium in Agriculture website. 

SARDI investigates K responses in SA with support from HiFert and Canpotex

In 2001, South Australian agricultural consultant, Stuart Roennfeldt noticed several paddocks showing areas of classic K deficiency symptoms which were also associated with windrow effects and early wilting of crops.  Plant tissue samples from good and bad areas showed a stark contrast in K concentrations, suggesting deficiencies despite the soils being relatively heavy textured and K responses being unknown in the region.  In order to properly determine the extent of K deficiency and possible management options, Stuart contacted SARDI crop nutrition specialist, Nigel Wilhelm.  With assistance from Hi-Fert and Canpotex, SARDI have established a comprehensive field trial incorporating a range of K rates, interaction with N and P and several application options.  For more information contact Nigel Wilhelm on (08) 8303 9353 or by email. 

University of Sydney students tackling K issues in vertosols

Two University of Sydney students under the supervision of Balwant Singh from the Department of Agricultural Chemistry and Soil Science are investigating the K dynamics in vertosols and its impact on crop performance.  

PhD student Sevag Bedrossian is completing research into the relationship between soil K pools and the incidence of premature senescence in cotton.  Sevag has studied the soils from paired sites which are, or are not, susceptible to premature senescence symptoms.  He is searching for differences in the size or rate of release of soil K pools, which may in turn be related to the mineralogy of the soil and the paddock history.

Fourth year honours student Mitchell Carter is conducting a pot trial to determine the fate of K fertiliser when applied to two vertosol soils.  The soils were collected from sites at Quirindi, NSW and Comet, Qld which have a history of silage maize production and have recently displayed K deficiency symptoms on maize crops.  At both sites, field-applied K was unable to produce significant yield improvements.  

For information about either of these projects contact Balwant Singh on (02) 9351 2237 or by email. 

AgResearch gauging potential for K responses in New Zealand hill country

Hill country pastures in NZ have not traditionally received K fertilisers.  It is recognised, however, that on hill country pastures significant transfer of K occurs from steep to easier slopes and that this will be exacerbated as pasture use intensifies with increased use of N fertilisers.  It is possible that K may be limiting pasture production in hill country, particularly on some landscape positions.  The role of K in maintaining the legume content of pasture may also be important where N fertiliser is applied.  

Researchers from AgResearch at Palmerston North are already involved in studying the differential responses to N and P fertiliser across varying hill country landscape positions in a major project funded by Ravensdown Fertiliser Co-operative.  With the support of Canpotex, they are taking the opportunity to gauge the impact of grazing, landscape position, N and P application on soil and plant K status in hill country.  For more information on this work contact Allan Gillingham, Senior Scientist, AgResearch on +64 (0)6 356 8019 or by email.  

K Questions

Answers to recently posed questions on K nutrition:

A grower asks: "What effect does the Cl in muriate of potash (MOP) have on soils and crops?"

Answer:  MOP is potassium chloride and by weight contains 50% elemental K and 46% Cl.  In most K responsive grain cropping situations MOP application is around 50-100kg/ha, or  23-46kg/ha of Cl.  This is around the same amount of Cl that is received in rainfall in most parts of Australia each year.  

Choride is an extremely mobile ion and isn't held by the soil.  So long as water is draining through the soil profile Cl will be moving with it.  Most problems with Cl arise when rising water tables bring up salts, including Cl salts, from below the root zone and evaporation concentrates it on the soil surface.  In high concentrations, Cl can have a toxic effect and inhibit the uptake of water by plants.

On the other hand, some soils can be deficient in Cl, particularly in semi-arid inland areas where little Cl comes from oceanic influences or in rainfall.  In the US states of Montana and South Dakota, wheat crops have suffered from Cl deficiencies and have shown yield responses to the Cl component of MOP, rather than the K component.  For more information on this work view the Potash and Phosphate Institute's Chloride Site on the web.

Some people can confuse the Cl in MOP with pool chlorine and have concerns that the use of MOP will "sterilise" the soil.  Pool chlorine is either calcium hypochlorite (powder) or sodium hypochlorite (liquid) and produces hypochlorite and chlorate ions in water, both of  which attack the cell walls of bacteria.  The chloride ion does not act in this way.  In fact where K is deficient, application of MOP will increase plant production and organic residues, which means more food for soil microbes and thus an increase in soil microbial biomass.  

Part of this confusion may have arisen due to the positive impact MOP can have in reducing the impact of plant pathogens.  For example, where K or Cl are deficient, MOP has been shown to increase the resistance of wheat to foliar fungal diseases and to take-all and common root rot.  Rather than having a direct impact on the pathogen, the effect is usually a result of increased resistance by the plant either through improved cell strength, or altering the plants metabolic compatibility as food for the pathogen.

Recently published papers

Recently published scientific papers examining issues of potassium nutrition:

Bolland, M.D.A., Cox, W.J. and Codling, B.J. (2002). Soil and tissue tests to predict pasture yield responses to application of potassium fertiliser in high-rainfall areas of south-western Australia. Australian Journal of Experimental Agriculture 42, 149-164

Li, H., Yang Xiao, E., Luo, A., Li, H., Yang, X.E., and Luo, A.C. (2001). Ameliorating effect of potassium on iron toxicity in hybrid rice. Journal of Plant Nutrition  24, 1849-1860.

Morton, J. D., Smith, L. C., Dodds, K. G., and Catto, W. D. (2001). Balanced and adequate potassium and phosphorus nutrition of pasture. New Zealand Journal of Agricultural Research  44, 269-277

Murthy, S. V. K., and Kotur, S. C. (2001). Dynamics of nitrogen, phosphorus and potassium redistribution in declining 'Thompson Seedless' grape (Vitis vinifera) vines. Indian Journal of Agricultural Sciences  71, 255-257

Wang, J. J., and Scott, A. D. (2001). Effect of experimental relevance on potassium Q/I relationships and its implications for surface and subsurface soils. Communications in Soil Science and Plant Analysis 32, 2561-2575

The Potassium Newsheet is part of the wider Potassium Development program which provides agronomic information on potassium nutrition of crops and pastures through publications, workshops and a website. The program also supports research and development into the best management practices for potassium fertilizer use in Australian and New Zealand agricultural production systems.

A wheat crop in WA showing effects from the windrows of a previous crop.

The site of a comprehensive K trial at Laura in South Australia.

On hill country, grazing animals transfer K from steep slopes to the easier slopes on ridgetops where they prefer to camp.

If you believe that a colleague would like to receive the Potassium Newsheet forward them a copy of this issue.  They can subscribe by clicking here.

In This Issue:

WA: Windrow effects highlight the need for K

SARDI investigates K reponses in SA

University of Sydney students tackle K issues in vertosols

AgResearch gauging potential for K responses in NZ hill country

K Questions

Recently published papers