Studies on soil potassium. II. The Q/I relation and other parameters compared with plant uptake of potassium

Abstract

Setaria (Setaria sphacelata cv. Nandi) was grown in 10 surface soils, of contrasting properties, in pots until (after repeated harvesting of tops) plant growth virtually ceased. Uptake of potassium by tops and roots was correlated with change in exchangeable potassium during cropping, initial exchangeable potassium, and with quantities of potassium predicted from the immediate Q/I relations of the soils. Some initially non-exchangeable potassium was absorbed from seven of the soils by the plants, such that these soil quantity parameters (which were statistically equivalent) predicted two-thirds of the total potassium uptake averaged over all soils. Potassium uptake was also correlated with soil potassium soluble in constant-boiling hydrochloric acid, and with potassium extracted by a cation exchange resin (both of which predicted about twice the plant absorption). For six of the soils, uptake of initially non-exchangeable potassium was correlated with the quantity of total potassium present in each pot in the 1 0 . 1 pm clay fraction. The intensity of soil potassium (measured in dilute calcium chloride solution from the immediate Q/I relation) was reduced on all soils by exhaustive cropping to a mean value for the equilibrium activity ratio (AR0) of 4.7 10-4 mole1/2 L.-1/2 (�G = -4500 cal equiv.-1); it was suggested that the observed variations in this value were unlikely to prohibit its use for practical soil testing, except for the prediction of the quantity parameter for those soils for which the form of the isotherm is altered by cropping. A tentative value for the potential of soil potassium at which setaria has an adequate average potassium concentration in its tops was - 3600 cal equiv.-1 (AR0 2.1 x 10-4 mole1/2 L.-1/2).

Critical potassium potentials for crops. I. The effect of soil type on the growth of ryegrass and creeping red fescue

“…The range of dG,,h values obtained (-17.5 to -28.2 and -18.5 to -3 1 .O kJ mol-1 for ryegrass and fescue respectively) was of a similar order to that obtained by Fergus et al (1972) for setaria by exhaustive cropping of 10 soils ( -17 to 29 kJ mol-I), although the clay content of their soils ranged from 3 to 63 per cent clay, a greater range than examined here.…”

“…Potassium exhaustion potentials (dG,,h) for crops are difficult to measure in soils because, as the soil is stressed, K is released from initially non-exchangeable sources. dG,,h is determined by (1) the extrapolation of the 'K removal vs potential' relationship to the K potential which gives minimum K uptake (Koch et al, 1970;Fergus et al, 1972); ( 2 ) determination of the AG values at which K uptake correlates best with corresponding dK value in the quantity : potential relationship (Addiscott, 1970); (3) exhaustive cropping to determine the potential corresponding to zero yield production (Talibudeen and Dey, 1968a, b;Addiscott and Johnston, 1975). Results obtained by these methods were summarized by Talibudeen and Page (1978).…”

A Study of the Quantity/Intensity Relationships of Potassium in Some Calcareous Soils of Iran

“…Many workers used Q/I parameters for fertilizer recommendations for different field practices and soil in various regions (Fergus et al, 1972;Singh and Jones, 1976;Sinclair, 1979;Sparks and Liebhardt, 1981;Evangelou and Blevins, 1988).…”

“…In correlation studies, the parameters of Q=I alone or in combination have sometimes been shown to be a better prediction of K þ uptake by plants than exchangeable K þ measured by 1 M NH 4 OAc and help in understanding the mechanism of the K þ supply to plants (Beckett, 1972;Evangelou et al, 1994). Many workers used Q=I parameters for predicting K þ requirement of soils (Fergus et al, 1972;Singh and Jones, 1976;Sinclair, 1979;Sparks and Liebhardt, 1981;Evangelou and Blevins, 1988).…”

Potassium Buffering Potential in Some Burne Soils of North Iraq

“…If, however, a Q/I is to be of any value in indicating the amount of soil K available for uptake duringthe growing season, its form must be unaffected by the amount of K fixation or release that is likely to occur during one growing season. Fergus et al( 2005) Hamed and Amin, (2017) have reported that K uptake by growing plants generally affects the pool of readily available K forms, and moreover, these changes, if considerable, might be expected to alter the form of the Q/I of a soil. Since plant growth is not directly limited by the amounts of exchangeable soil K, therefore it should be necessary to elucidate this phenomenon on the basis of equilibrium studies in order to test the immediate power of soils to supply K to plants.…”