Research Findings: e-ifc No. 16, June 2008

Potassium improves grain filling - a short story in pictures and figures from India, Indonesia and China

Potassium improves grain filling of wheat
Results shown here are the average figures for 24 plants from five varieties and four replicates.

The yield of a grain crop depends on (a) the number of ears per unit area, (b) the number of ripe grains per ear, and (c) the weight of the grain (the so called 1000 grain weight). Due to its influence on photosynthesis and assimilate transport, potassium is particularly effective in the improvement of grain number and (1,000) grain weight. This has been confirmed not only in pot experiments with wheat, as shown in the Fig. 1, but also in numerous field trials with this and other cereal crops, as demonstrated in the next photos and figures obtained from various experiments in which IPI is involved.

Fig. 1. Effect of exchangeable K in soil on yield and its components in wheat. Source: Slide #6; IPI slides on Potassium in plant production. This and other slides are available on the IPI website

Wheat in India
Plate 1 reveals a typical response of K application to wheat. The wheat crop was grown on a low K soil (30 mg/kg) and received 120 and 60 kg N & P₂O₅, respectively, with an additional 60 kg K₂O/ha to the K+ plot. As shown, grain filling is much improved with potassium application. Source: IPIICAR experiment, India. 2004.

Plate 1. Wheat grain in response to K application. Photo by S. Bansal, Potash Research Institute of India (PRII).

Potassium increases grain filling in rice: an example from Indonesia.
Plate 2 shows a typical response of K application in rice, through better grain filling. The picture shows a panicle and the grain removed from it taken from a plot not fertilized with K (left) compared with that from a plot fertilized with K (right). Grains from the panicle were removed and categorized as i) unfilled, ii) partially filled and iii) fully filled. In both samples, the grains at the top are those unfilled, the grains in the middle are partially filled, and the grains on the bottom are filled. Clearly, the sample from -K has a much larger proportion of unfilled and partially filled grain.

Plate 2. Potassium application improves grain filling in rice. Photo by R. Buresh at an SSNM field, 2006, Indonesia.

Potassium increases grain filling in maize: an example from Sichuan, China.
The effect of K fertilization on grain filling of maize is shown in Plate 3. The picture was taken at IPI-SFI Chengdu project in maize-sweet potato-winter wheat intensive cropping system. Both treatments received the recommended dose of 230 kg N/ha and 90 kg P₂O₅/ha. The +K plot received 175 kg K₂O/ha.

Fig. 2. Effect of potassium and OM on grain yield, during 1998 and 1999. Vertical bars represent LSD at 5% probability. Source: IPI-SFI report by Chen Yibing, SFI Chengdu, 2001.

The results from this experiment demonstrate how the application of both potash and organic matter (OM) had a significant effect on grain weight during 1998 and 1999 (Fig. 2). Interestingly, application of OM had a positive effect on grain weight in both years, especially at K=0, suggesting that the potassium in the OM is important as a nutrient input, and has to be calculated accordingly.

Plate 3. Potassium application improves grain filling in maize. Photo by H. Magen.

Plentiful, nourishing maize grain used for food, fuel, or industrial uses. For any use, grain has to exhibit optimal internal and external qualities.