Extreme potassium deficiency in cotton fields can cause large numbers of plants to die

Cotton is a crop sensitive to potassium deficiency, especially since the development of BT transgenic insect-resistant cotton, potassium-deficient cotton fields often show severe disease, premature aging, few and small bolls, poor boll opening and deteriorated fiber quality. Four or five years ago, rapid soil nutrient tests on cotton fields in central and southern Hebei showed that most soils had available potassium content below 80PPM (mg/kg), which is severe potassium deficiency, and some soils were below 40PPM, reaching the level of extreme potassium deficiency. The data measured by soil nutrient rapid testers is not precise; some soil samples measured available potassium content of 0, and this situation has appeared at many testing points, showing how severe the degree of potassium deficiency is.

Because of the advocacy and practice of increasing potassium fertilizer application, the number of cotton farmers applying potassium fertilizer and cotton formula fertilizer with high potassium content has increased year by year, all of which have played a role in controlling disease and increasing yield, and the available potassium content in the soil has also recovered and increased, but some cotton farmers still have misunderstandings, believing that compound fertilizer (most of which contains nitrogen, phosphorus and potassium in a ratio of 1:1:1) contains potassium and can replace potassium fertilizer application, or using high-concentration compound fertilizer containing 19% each of nitrogen, phosphorus and potassium to replace applying more potassium fertilizer, and some cotton farmers mistakenly believe that “potassium sulfate compound fertilizer” is potassium fertilizer, with the result that they spent no less money but did not achieve the potassium supplementation effect.

Recently there has been more cloudy and rainy weather in the north, and temperatures have dropped. Some cotton farmers report that in some cotton fields the whole plant's cotton leaves first turn yellow and then wither, and the plants even begin to die, and some believe it is an outbreak of verticillium wilt. The most important basis for judging whether it is fusarium or verticillium wilt is to split the stalk; as long as the xylem of the cotton stalk has not turned brown, fusarium and verticillium wilt can be ruled out, and the cotton field is very likely caused by extreme potassium deficiency (potassium deficiency can also induce disease and worsen the condition), with severe performance in low-lying areas, places where water has accumulated, and cotton plants with many bolls, and in the most severe cases even all cotton plants in the field prematurely age and die, and the author sees such cotton fields every year; while cotton fields with increased potassium fertilizer application will not cause or produce large numbers of dead plants in the later stage.

Why do some cotton fields following corn also have large numbers of dead plants? Because corn is a crop that needs much potassium and has a strong ability to absorb potassium, if the corn field does not contain much potassium and the corn yield is high, the available potassium in the soil is almost completely consumed by the corn, and if cotton is planted after switching crops without increasing potassium fertilizer application, it will likewise cause large numbers of dead plants, and there are many such lessons.

Cotton plants beginning to show potassium deficiency mostly start in early August from the lower old leaves; after heavy rain, and after setting more cotton bolls, spraying potassium fertilizer 3 times in succession at this time will not cause large numbers of dead plants in the later stage. In mid-August, if some cotton plants show potassium deficiency but the upper part still has green leaves, and potassium is supplemented promptly, losses can still be reduced. If now the upper leaves of the cotton plants have all withered, and most cotton plants have already withered, then supplementing potassium is too late.