Thursday, June 24, 2010

Sulfur and Potassium Deficiency in Rice

During the past few days, we have received a few calls about suspected sulfur and potassium deficiency in rice. The deficiency symptoms can be confusing and hopefully we can provide some assistance in distinguishing these problems from other stem and leaf diseases.

Sulfur deficiency of rice: The following images show leaf symptoms of sulfur deficiency. We rarely see this in Arkansas and it is usually in patches or areas of fields, often associated with sandy regions but may be reported on “cut” spots as well. In the latter, it may be associated with other deficiencies from what we have observed.

Sulfur deficiency shows up in the upper leaves, from a distance appearing dull or bright yellow, at least at first.

Closer examination may show shortened leaves with tip discoloration (yellowing) following by the formation of rows of brown spots between the veins proceeding from the tips downward.

Another view of the tip discoloration and the spotting between veins.

Potassium Deficiency: Many silt loam rice soils in Arkansas are low in available potassium. Rice grown on these soils is subject to potassium deficiency, which often gets noticed during the early to mid booting stages, and to more severe stem rot and brown spot.

As shown above, potassium deficiency may show up as a later season tip discoloration. From a distance, patches in the field may turn reddish or brown and seem to spread across the field over time as the plants become deficient over larger areas. Wells rice shows this symptom as reddish tip discoloration, and the affected length of leaves may be several inches from tip downwards.

If you examine rice plants in suspected potassium deficiency areas, you may find increased disease symptoms of stem rot as above, in severe cases killing the stems resulting in partially blanked discolored panicles.

You may also notice severe brown spot as above. This often occurs on deficient Bengal and other rice varieties.

Sometimes, rice developing deficiency earlier in the season will be stunted, with more yellowing of the tips of the lower leaves and tip discoloration.

An unexplained tip discoloration symptom that shows up during booting is the so-called “high yield disease”. Sometimes lush, rapidly growing rice fields will exhibit widespread tip discoloration of the field usually on the 3rd leaf down. This is the leaf that is sticking up the tallest for a while at early boot, until the flag and flag minus one leaves are fully developed. The discoloration is usually yellowish to a light brown and the leaf tips may have some spots, etc on them, however tip discoloration is very mild and remains so compared to true deficiencies which continue to move down the leaf tips pretty quickly. The above phenomenon has been associated with lush, high yield potential fields in the past, thus the nickname.

If caught in time, nutrient deficiencies may be stopped by the application of “rescue” fertilizer applications but these attempts are too late to prevent yield losses. They may stop progression of the symptoms or help slow diseases a bit. Greater success for salvaging these situations is achieved with early detection.

One of the biggest challenges with potassium deficiency is what is known as “hidden hunger”. This occurs when the plants are slightly deficient in potassium but no visable deficiency symptoms are displayed by the plant. Because of this situation, we strongly recommend adequate soil sampling and application of preplant potassium as recommended. We have observed significant yield increases from potassium from plots exhibiting only mild or no deficiency symptoms until it is too late.


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  2. Good information for young & new farmers