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Fertilizing Rice with Sulfate of Potash PDF Print E-mail

Rice is the most consumed cereal in the world. Nowadays, high crop intensification has caused rapid depletion of soil potassium (K), which may result in more frequent K deficiencies. A previous study showed that addition of K, as sulfate of potash (SOP), could improve rice yield in comparison to another K source.

    Rice is a major staple crop, supplying carbohydrates for more than half of the global population. China and India are the major rice producers and consumers. Four rice types are cultivated globally: a) indica, cultivated in tropical and subtropical regions and the most cultivated type (about 75% of total rice production); b) japonica, characteristic of cooler climates; c) aromatic, a premium type produced in Thailand and Pakistan (jasmine and Bastami); and, d) glutinous, cultivated mostly in Southeast Asia, commonly used for desserts.

    Potassium rates should be applied according to plant requirements but also considering soil K status to avoid plant nutrient deficiencies and soil K depletion on the short and long terms. Rice K uptake at optimum nutrient levels is about 19 kg K2O per ton of grain yield. Recommended application rates based on soil K status and desired yields are show in Table 1.

Table 1. Recommended potassium rates (K2O form) for rice production based on yield targets and K soil status (modified from: Rice Knowledge Bank, 2017).

Yield target (t/ha)

4

5

6

7

8

Soil K status

Yield in with
no K app (t/ha)

Recommended fertilizer K2O in kg/ha

Low

3
4

30
0

60
35

90
65


95


Medium

5
6

-
-

20*
-

50*
35*

80*
65*

110*
95*

High

7
8

-
-

-
-

-
-

50*
-

80*
65*

< Unachievable yield goal. *Lower K2O rates by about 20-25 kg K2O/ha, if 4-5 straw/ha are returned after harvest,
if K rich sediment inputs are high or if long-term experiments indicate high soil supplying power.
Increase in K2O rates by the same amount, if straw is fully removed after harvest.

    In rice, K deficiencies appear as general dark green color with stunted growth. Older leaves become yellow in the edge and later turn necrotic. If not treated, K deficiencies may result in reduced plant growth, panicle size and number, leading to detrimental rice yields (Figure 1).

Effect of potassium deficiencies in rice: Reduced panicle size (a), reduced plant (b) and panicle size and grain number (c; source: International Potassium Institute).
Figure 1. Effect of potassium deficiencies in rice: Reduced panicle size (a), reduced plant (b) and panicle size and grain number (c; source: International Potassium Institute).

    Among the most common K sources, SOP should be considered to supply K, especially under saline conditions. Additionally, SOP provides sulfur (S) and K at readily available form, improving nutrient availability for plants. This fertilizer can be applied either a soil application or as supplemental foliar application during the season. Supplemental foliar applications may range between 1 and 6% of SOP solution depending on K soil and plant status (Ali et al., 2007).

    Ashraf et al., (2009) conducted a study to explore the effects of K sources and supplementary foliar applications of Zinc (Zn) and K on yields of two rice cultivars. Application rate of K to the soil was 90 kg/ha as K2O applied using SOP and KCl (MOP) as K sources. Supplementary foliar applications were 35% Zn (1% ZnSO4.H2O) and/or 1% SOP solution. Results showed that SOP resulted in higher number of filled spikelets and higher yields in salt tolerant cv. Shaneen Bastami, especially when supplemental foliar Zn was applied (Figure 2).

Effects of K sources and supplementary foliar zinc (Zn) and K applications on rice number of filled spikelets and grain yield for a tolerant cultivars, Sheikhupura, Pakistan (modified from SOPIB, Ashraf et al., 2009).
Figure 2. Effects of K sources and supplementary foliar zinc (Zn) and K applications on rice number of filled spikelets and grain yield for a tolerant cultivars, Sheikhupura, Pakistan (modified from SOPIB, Ashraf et al., 2009).

    Monitoring soil K levels early in the season help to determine K application rate. In general, sandy soils, acid upland soils, degraded soils, acid sulfate soils, and organic soils show low K levels for crop growth; therefore, high K rates in split applications should be considered. Balance soil nutrition will help to improve and maintain rice yields.

    Full articles:

Ali, A; Mahmood, IA; Hussain, F; and Salim, M (2007). Response of rice to soil and foliar application of K2SO4 Fertilizer. Sarhad Journal of Agriculture, 23(4), 847.

Ashraf, M; Hussain, F; Mahmood, K; Akhtar, K; Yaqub, M; Hassan, M; Farid, G; and Marchand, M (2009). Improvements in yield and salt tolerance potential through potash (SOP) fertilizer in wheat and rice grown on salt-affected soils. Third annual report, SOPIB.

Abdulrachman, S; Witt, C; and Buresh, RJ (2006). The need for potassium fertilization in rice and experiences from a long-term experiment in Indonesia. E-IFC no. 10, International Potash Institute. www.ipipotash.org/eifc/2006/10/6. Available at: https://www.ipipotash.org/fr/eifc/2006/10/6#f1

International Potash Institute (2017). Gallery of rice potassium deficiency symptoms. Available at: https://www.ipipotash.org/en/kgallery#ipi-slide120

International Rice Research Institute (2017). Potassium. Available at: http://www.knowledgebank.irri.org/training/fact-sheets/nutrient-management/item/potassium-k

 
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