Potassium Newsheet   Vol 1 Iss 3 : Summer 2002

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WA: Revitalising waterlogged pastures with new species and better management - including K application

Rising water tables and encroaching salinity have led to the degradation of up to 100 000ha of low lying pastures in the Blackwood River catchment in the WA woolbelt.  Productive clover-based pastures have been replaced by poor quality but adapted species such as sea barley grass.  Previous trial work by the WA Department of Agriculture has shown that some productive pasture species which are tolerant of waterlogging and saline conditions, such as balansa clover, can be successfully grown in these areas.   Establishment of a successful pasture assists in rehabilitating these areas by ensuring a greater use of soil moisture and therefore combating waterlogging and salinity, as well returning economic value to these land areas.  However, the persistence of introduced species depends on good management, including nutrition, weed control, redlegged earth mite control and grazing management.  In particular, balansa clover has a high requirement for potassium and deficiency results in poor seed set and regeneration.  

A group of graziers on the Beaufort Flats near Kojunup, with assistance from agronomist Brian Leach of John Duff and Associates, are testing pasture species and the application of management options to rejuvenate pasture on valley floors.  The group are receiving assistance from Department of Agriculture officers, CSBP futurefarm and the Canpotex Potassium Development Program.  For more information on the activities of the Beaufort Flats Group contact Brian Leach by email or on (08) 9475 0753. 

Researchers collaborate to tackle K issues in northern cropping systems

Researchers from the northern grains, cotton and sugarcane industries met in Toowoomba in July to compare industry K nutrition issues.  Mike Bell, Wayne Strong and Rob Kelly (Qld Department of Primary Industries) outlined K issues in the grain cropping regions, Bernhard Schroeder (Bureau of Sugar Experimental Stations) and Andrew Wood (CSR) presented recent work undertaken in the cane industry (see below), Ian Rochester (CSIRO Plant Industry) described K nutrition problems in the cotton industry and Phil Moody (Qld Department of Natural Resources) highlighted some of the lab-based work recently undertaken in an attempt to describe soil K dynamics.   The University of Queensland, the University of Sydney and the fertiliser industry are also represented in the group.

Some K nutrition issues were common across the industries including the assessment of soil K supply, the impact of soil type on fertiliser K requirements, the influence of other cations on K uptake and interactions between cropping system, soil moisture, form and placement of K fertilisers.   A collaborative effort to solving these problems was proposed.  The appropriate funding bodies are being approached to contribute to a joint effort to address K nutrition issues, along with support from the fertiliser industry.  For more information on the issues being addressed or on the collaborative efforts of the research group contact Mike Bell on (07) 4160 0730 or by email.  

K recommendations for cane should consider soil type

Recent work undertaken by cane industry researchers Bernhard Schroeder (BSES) and Andrew Wood (CSR), has led them to question the need to review K fertiliser recommendations for sugarcane.  Current recommendations are based on critical soil exchangeable K levels, adjusted based on nitric acid K extractions where available.  Analysis of trial data has shown that soil K requirements for maximum yield vary with soil type, with critical exchangeable K values in the heavier textured soils being higher than those for sandy textured soils.  The researchers summarised their findings in a paper presented to the conference of the Australian Sugar Cane Technologists in May 2002.  For more information contact Bernhard Schroeder by email or on (07) 4132 5200. 

Clay mineralogy affects K dynamics in Vertosols

A recently completed honours project by University of Sydney student, Mitchell Carter, has shown that small differences in the mineralogy of Vertosols can have a major influence on their K dynamics.  Mitchell studied the K dynamics in two Vertosols which had been used to produce silage maize crops and where K deficiency symptoms had been seen in the field (Potassium Newsheet Vol1 Iss2).  Whilst there was no impact of K fertiliser application on maize growth in glasshouse pot trials, there was a distinct contrast between the soils in terms of K dynamics and it appeared that this was related to differences in clay mineralogy.  In the first soil which contained slightly more illite, K appeared to be released from the mineral structure and eventually into the soil solution for plant uptake, while in the second soil containing more smectite, added K was fixed and did not contribute to plant available K.   Continuous removal of the interlayer K in illite can lead to its weathering to form smectite, therefore the mineralogy of the second soil could be a result of long-term removal of K in hay or silage.  Application of fertilisers to a K-fixing soil in order to shift the equilibrium back to K release for plant growth would is expensive.  This study has highlighted the importance of fertiliser programs which replace exported K on Vertosols and the need to understand the fate of applied K in individual soils before undertaking field trials.  For more information on the study contact the project supervisor Dr Balwant Singh by email or phone (02) 9351 2237.

GRDC supports research on K nutrition in WA

In 2003 the GRDC will be supporting several projects in Western Australia which address some aspect of potassium nutrition.    

A major project to review soil fertility constraints in WA cropping systems and to collate existing knowledge  into decision support systems for use by growers or their advisers is currently on the drawing board.  Dr Bill Bowden from the Department of Agriculture will lead this project which will draw on the outcomes of previous and current nutrition work undertaken by the department on potassium nutrition, micronutrient nutrition in no-till systems, subsoil acidity management, row spacing and nutrient placement.  For more information on this project contact Bill Bowden by email or on (08) 9690 2000.

The GRDC has announced funding for a project led by Prof Zed Rengel from the University of Western Australia which will attempt to quantify the K cycling within cropping systems in the state.  The project was prompted by observations that K added in fertiliser could not be accounted for in product removal or changes in Colwell extractable soil K.  It is hoped that this project will provide more information on the movement of K between pools, spatially and temporally, including the fate of added K.  For more information on this project contact Zed Rengel by email or on (08) 9380 2557.

Finally, GRDC is supporting a project to evaluate agronomic techniques for minimising frost damage in wheat, an issue which costs WA farmers an average of $5 million each year in lost yield.  The techniques being evaluated include wider row spacing (which has been shown to increase air temperatures at seed head height), claying, nitrogen and potassium applications.  Overseas, potassium application to overcome K deficiencies has been shown to contribute to increased frost tolerance in potatoes, grapevines and some treecrops.  For more information on the frost minimisation project contact Garren Knell of Consult Ag by email or on (08) 9881 5551.   

K Questions

Answers to recently posed questions on K nutrition:

An agronomist asks: "Does the concentration of K in wheat grain tell me anything about the K fertility of the paddock?"

Answer:   The concentration of K in grain usually doesn't vary much, regardless of the K availability in the soil.  Most of the K absorbed by crop plants remains in the vegetative plant parts, rather than being translocated to the grain as the crop nears maturity, as occurs with N for instance.   This is particularly so with cereal crops where K harvest indices are typically around 20-30%, compared to legume crops which may have a K harvest index of around 50%.  There is usually sufficient K available in the vegetation of cereal crops to result in normal grain K concentrations even if there is shortage of K for maximum dry matter production.

Protein content and grain size may be more useful post-harvest indicators of K availability during crop growth.   This is because of the roles played by K in translocating photosynthates to the grain and in determining both the rate and the period for which grain is filled.  Yield increases due to K fertilisation are often as a result of increased grain size.

By far the most reliable method of detecting K deficiencies using plant analysis is by collecting tissue from the correct plant part at the correct stage during vegetative growth.  However, if a K deficiency is suspected after the crop has matured, the best way of confirming this is by applying strips of K at a couple of varying rates and monitoring next year's crop.

Recently published papers

Recently published scientific papers examining issues of potassium nutrition are listed below.   A searchable database of abstracts of scientific papers addressing issues of potassium nutrition is available on the Potassium in Agriculture website, where links to the home pages of relevant journals are also provided for anyone wishing to purchase full copies of individual papers.

Maser, P, Gierth, M and Schroeder, J.I. (2002). Molecular mechanisms of potassium and sodium uptake in plants.  Plant and Soil 247 (1): 43-54

Pal, Y, Gilkes, R.J., and Wong, M.T.F..  (2002). Mineral sources of potassium to plants from seven soils from south-western Australia.  Australian Journal of Soil Research  40 (8): 1357-1369.

Regmi A.P., Ladha J.K., Pasuquin E, Pathak H, Hobbs P.R., Shrestha L.L., Gharti D.B. and Duveiller E.  (2002). The role of potassium in sustaining yields in a long-term rice-wheat experiment in the Indo-Gangetic Plains of Nepal. Biology and Fertility of Soils  36: 240-247.

Singh, K.N., and Sharma, D.P.  (2001).  Response of wheat to nitrogen and potassium in saline soils.  Experimental Agriculture 37: 417-427

Singh, M, Tripathi A.K., and Damodar Reddy, D.  (2002).  Potassium balance and release kinetics of non-exchangeable K in a Typic Haplustert as influenced by cattle manure application under a soybean-wheat system.  Australian Journal of Soil Research 40: 522-541.

Yin, X and Vyn T.J.  (2002). Residual effects of potassium placement and tillage systems for corn on subsequent no-till soybean. Agronomy Journal  94: 1112-1119.

Yin, X and Vyn T.J.  (2002). Soybean responses to potassium placement and tillage alternatives following no-till. Agronomy Journal  94: 1367-1374.

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.

Beaufort Flats grazier, John Pickford, stands knee-deep in a balansa clover and tall wheatgrass pasture on a previously water-logged valley floor.

Severe K deficiency symptoms on sugar cane.  Symptoms include slender stalks, chlorosis of the older leaf tips and borders and sometimes a red discolouration of the upper surfaces of the the midrib.

Availability of K can impact on individual grain size.  In this WA trial, the larger grains on the right came from plots which had received K fertiliser, whilst the smaller grains on the right were from the control.       (Photo courtesy of CSBP futurefarm)

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In This Issue:

WA: Revitalising waterlogged pastures with new species and better nutrition

Researchers collaborate to tackle K issues in northern cropping systems

K recommendations for cane should consider soil type

Clay mineralogy affects K dynamics in Vertosols 

GRDC funds projects in WA 

K Questions

Recently published papers