Management and Dynamics of Potassium in a Humid Tropical Ultisol under a Rice‐Cowpea Rotation

Abstract

Little is known about the role of K fertilization, stover management, and tillage methods on soil K availability as they affect rice (Oryza sativa L.) and cowpea [Vigina unguiculata (L.) Walp.] productivity on Ultisols of the humid tropics. The effects of five K rates (0‐120 kg K ha−1), returning or removing stover, and three tillage methods (no‐till, strip, and conventional) were evaluated during 12 crops of rice and cowpea grown for a 4‐yr period. Fertilizer K was applied to the first seven crops. The site was a recently cleared, 18‐yr‐old secondary forest in the Peruvian Amazon Basin. The soil was a fine‐loamy, siliceous, isohyperthermic Typic Paleudult. Soils samples were collected at each crop harvest to 90 em in 15‐cm increments. Potassium fertilizer always increased grain yields when stover was removed. Conversely, responses to K additions were seldom obtained when the stover was returned. The extractable K (Modified Olsen) critical level for both upland rice and cowpeas was calculated to be 0.10 cmol L−1. Returning stover with no K fertilization maintained soil K concentrations above critical levels for both species up to the last crop of the rotation. Residual effects of fertilizer K were prolonged by returning the stover. When stover was returned, subsoil exchangeable K increased with increasing rate of K fertilization. Removal of stover resulted in greater increases in subsoil exchangeable K at the 40 kg K ha−1 rate than at 120 kg K ha−1, apparently because the higher rate resulted in K fixation. Tillage methods did not affect crop yields.

The potassium paradox: Implications for soil fertility, crop production and human health

“…These consequences are to be expected considering the ample evidence in Table S4 (for the online version of the paper) that KCl inputs are often ineffective for increasing yield, but will be more serious when yield is depressed. The latter effect has indeed been observed, and was significant in field studies with corn 38,144,148,192 , soybean 120,125,131,175 , wheat (Triticum aestivum L.) 186 , sugarbeet (Beta vulgaris L.) 139 , sugarcane (Saccharum officinarum L.) 127 , alfalfa 145 , peanut (Arachis hypogaea L.) 109,191 , rape (Brassica napus L.) 176 and cowpea (Vigna unguiculata L.) 166 . In several of these studies, the loss of yield was intensified by increasing the rate of KCl application 38,109,120,125,175,192 , and in some cases the higher rate transformed significant yield gain to loss 127,186 .…”

Validation of Soil‐Test‐Based Phosphorus and Potassium Fertilizer Recommendations for Irrigated Soybean

“…Research with flood-irrigated rice has shown weak or no significant correlation between relative rice yield or growth and soil-P availability indices from various STP methods (Chang, 1978;Khalid et al, 1979;Shahandeh et al, 1994Shahandeh et al, , 1995. Limited research suggests that STK is meaningful for rice grown under flooded soil conditions, with STK explaining 41 to 61% of the variability in relative rice yield (Cox and Uribe, 1992;. Arkansas research has shown that Mehlich-3 extractable P is not a good predictor of rice relative yield (r 2 = 0.17) response to P fertilization .…”

Benefits of organic residues and chemical fertilizer to productivity of rain-fed lowland rice and to soil nutrient balances

“…because of immobilization of native soil N) and FNR was usually not significantly reduced when residues and fertilizer were applied together (Table 6). Many studies have shown the positive residual effect of straw incorporation on the K fertility status of upland and lowland rice systems (Cox and Uribe 1992;Prasad et al 1999;Dierolf and Yost 2000). Rice straw contains approximately 80% of the above ground plant K and can amount to over 150 kg K ha -1 (Dobermann et al 1996Dobbermann and Fairhurst 2000).…”