K in the Literature

Read and watch at:

How to Make Agricultural Extension Demand-Driven?
The Case of India. Agricultural Extension Policy. Birner, R., and J.R. Anderson. 2007. Discussion Paper 729, IFPRI, Washington, DC. http://www.ifpri.org/pubs/dp/ifpridp00729.asp or download at http://www.ifpri.org/pubs/dp/ifpridp00729.pdf
Food crisis spurs research spending. Butler, D. Nature, 453, 8 (2008). http://www.nature.com/news/2008/080430/full/453008a.html
IRRI Director General calls for another Green Revolution. Look at IRRI web site (You Tube) at http://ca.youtube.com/watch?v=nV46A8xnSFM

Long-term fertilizer experiments in China exist in many locations. In this picture, the station at Wangcheng, Hunan, is the key field monitoring experimental station for "Reddish Paddy Soil". The couple pictured have dedicatedly managed the experimental station since its start, in 1981. IPI conducted a field experiment at this station (2005-2007) to test the effect of potash on yield of paddy rice. Photo by H. Magen.

For more K literature go to www.ipipotash.org/literature
Note: All abstracts in this section are published with permission from the original publisher.

Potassium Requirements for Grass Cut for Silage - A Review

The management of productive grass swards is primarily driven by the appropriate use of relatively large dressings of nitrogen, both from fertilisers and manures. The basis for current fertiliser recommendations was laid by a large number of experiments carried out in the UK between the 1940s and 1960s. These experiments are identified and their findings reported. Both costs and outputs must be assessed. Increasingly aspects relating to water quality and pollution hazards to the environment must be considered. High yields of conserved grass inevitably remove large quantities of potassium from the field when harvested. This potassium must be replaced if soil fertility is not to decline. The percentage of potassium in the herbage DM (especially late in the previous season) is a good indicator of the essential need for potassium fertilisation. Values below 2.0% potassium are indicative of serious depletion which should receive attention. UK experiments suggest that optimum yields can be obtained when herbage potassium concentration remains above 3.0% DM at the end of the previous season. The critically important relationship between the requirements for nitrogen and potassium by high-yielding grass swards is discussed and the extensive experimental evidence is reviewed.

Potassium, Sodium and Magnesium in Grass and Animal Nutrition: A Question of Balance

Per se, or in relation to other nutritional requirements for optimised plant and animal performance, can be identified at an early stage. Knowledge of soil, field and farm K balances is one means of providing guidance on actions that may need to be taken from both tactical and strategic perspectives. Examples are provided of effects at various stages of the production cycle and of opportunities to improve balances. Potassium (K) is a key nutrient with widespread impact and functions within the complexity of grassland based livestock production. It has received relatively little research attention in recent years, but much is known about its behaviour, content and specific roles in each of the component parts of a livestock farm. Requirements for optimised supplies to forage crops are well known, as is K distribution and availability in soils. The interactions of K with other elements which are of importance to the nutritional well-being of livestock, especially lactating ruminants, have also been well described, and whilst the effects can be confounded by interactions with other factors, good advice is available to minimise risk. Nevertheless, it is timely to consider K in a more systematic way within the whole production cycle so that any potential imbalances in supply.

Effects of Potassium Supply on Growth and Yield of Safflower as Compared to Sunflower

Safflower may have a certain production potential under German conditions, particularly in organic farming where the putatively low nutrient requirement is highly welcomed. However, current knowledge regarding the nutrient requirements of safflower as compared to similar oil crops is limited. It was thus the aim of this study to determine the growth and yield response of safflower (Carthamus tinctorius L.) as compared to sunflower (Helianthus annuus L.) with respect to potassium (K) supply. Three safflower and two sunflower plants were cultivated in 5 L Mitscherlich pots. Both species responded strongly to increasing K supply with respect to plant growth and yield. Growth and yield of safflower increased up to 1 g K per pot, while the optimum for sunflower was 3.0 g K per pot. Safflower out-yielded sunflower at low K supply, while at high K level, the opposite was observed. Supply of K affected virtually all yield components in both species, though to different degree. The number of capitula in safflower was only slightly affected, and the number of achenes per capitulum was only reduced under severe K deficiency, while single-achene mass increased with increasing K supply. In sunflower, the number of achenes per capitulum strongly responded to the K supply, as did the single-achene mass. Oil yield in safflower was affected by K deficiency mainly due to reduced achene yield, not oil concentration. However, oil yield in sunflower was severely affected by low K supply due to both reduced achene yield and lowered oil concentration.

Multiple-regression analyses indicate that in sunflower, the stem dry matter (DM) and the total amount of K accumulated in the aboveground biomass were most important, while in safflower the total amount of K and N accumulated had the highest impact. It is concluded that sunflower is more sensitive to inadequate K supply than safflower.

Potassium Release in Representative Maize-Producing Soils of Thailand

Ammonium acetate K does not adequately measure available K in the mineralogically diverse maize (Zea mays L.)-producing soils of Thailand. The objective of this study was to understand the causes of this problem and propose a solution using laboratory and greenhouse experiments to examine the release patterns and the availability of exchangeable and nonexchangeable K. Eight kaolinitic and smectitic soils were examined for the release of K in each soil fraction (sand, silt, and clay) using the Ca-resin successive extraction method. The data were fitted using parabolic diffusion, power function, and segmented straight line regression models. The power function and the segmented regression model fitted the data well. All soils were exhaustively cropped with maize in the greenhouse until the soils became K deficient. The results indicated that a segmented regression model 2 described nonexchangeable K release to the Ca-resin and to plants in a way that seemed to correspond with earlier predictions. According to the model, there were two fractions of nonexchangeable K, which were released at distinctly different rates. The greenhouse study yielded fast and slow K release rates from the nonexchangeable K pool of 0.45 to 0.85 and 0 mg kg^-1 d^-1, respectively, in kaolinitic soils and 1.60 to 1.98 and 0.27 to 0.52 mg kg^-1 d^-1, respectively, in smectitic soils. Our results suggested that NH₄OAc-extractable K was suitable and sufficient to determine plant-available K in kaolinitic soils. In contrast, a successive Ca-resin extraction characterization plus NH₄OAc-extractable K was required to determine plant-available K in smectitic soils.

Potassium and Nitrogen Interactions in Crop Production

The potassium (K) status of the soil has a considerable influence on crop uptake and response to nitrogen (N). Yield response to applied fertiliser N is decreased by low concentrations of exchangeable in the soil. The basis of this interaction is explored using historical and current data from Rothamsted Research's experiments at Rothamsted, Saxmundham, Woburn and Broom's Barn on spring barely, winter wheat, potatoes, sugar beet mangels and grass. It is argued that the agronomic responses derive from the physiologically interacting effects of N and K on tissue hydration and consequential osmotic adjustments in shoot tissues.

Potassium and Magnesium in Manures and Organic By-Products

Potassium and magnesium are essential nutrients for crop development. In the context of the Nitrates Directive and the Water Framework Directive, the focus is directed more towards nitrogen and phosphorus than towards potassium and magnesium, mainly because K and Mg have no real direct effects on the environment.

In intensive agriculture the potassium and magnesium release from primary and secondary soil minerals is too low to compensate for the offtake by the crop. Besides mineral fertilisers, large amounts of potassium and magnesium can be applied to the soil via animal manures and other organic by-products. Concentrations of K and Mg in all kinds of animal manures, composts, spent mushroom composts (champosts) and some secondary materials originating from processing agricultural products are given for various countries. From this overview a large variation in K and Mg content is obvious between countries but even more in a specific country. Causes for this high variability are diverse but to a large extent due to differences in dry matter content and the original contents in the primary products.

It is generally accepted that the efficiency of K and Mg in animal manures and organic by-products is of the order of 80 to 100% compared to mineral K- and Mg-containing fertilisers. On the other hand, if applications of these organic materials are made during winter time, quite important losses, especially for potassium, can occur in light textured soils.

Knowledge of at least the order of magnitude of the potassium and magnesium contents in these organic materials is necessary for the promotion of a sustainable agriculture.