Assessment of potassium soil balances and availability in high yielding rice systems

Nutr Cycl Agroecosyst https://doi.org/10.1007/s10705-022-10200-w ORIGINAL ARTICLE Assessment of potassium soil balances and availability in high yielding rice systems Bruce A. Linquist · Johnny C. Campbell · Randal J. Southard Received: 20 September 2021 / Accepted: 2 March 2022 © The Author(s) 2022 Abstract Plant demand for K in rice is comparable to nitrogen. With yields and management practices changing, refining K fertility management and decision-making tools is necessary. Our objectives were to determine (1) how soil K balances affect soil K indices, (2) the best soil test indicator of plant K availability, and (3) the relationships between plant and soil K indices. We assessed soil (plow layer) and flag-leaf samples from 55 commercial rice fields in California. Growers provided historical information on K fertility practices, straw management, and yields to develop a soil K balance. A soil K balance average of − 15 kg K ha−1 yr−1 (range: − 72 to 47) suggested an increased likelihood of K infertility; however, K balance was not correlated with soil K indices or flag-leaf K. This, plus the potential for K losses and fixation of surplus K, suggests that attempting to build up soil K may not be an effective strategy. Soil K indices were poorly correlated with plant K, but 1 N NH4OAc-extractable K (Kext) was the best of the K indices tested. Soils that were low in Kext had low clay content, CEC, and K saturation, a high Ca + Mg:K ratio, and showed evidence of K fixation. B. A. Linquist (*) · J. C. Campbell Department of Plant Sciences, UC Davis, One Shields Ave, Davis, CA 95616, USA e-mail: R. J. Southard Department of Land, Air, and Water Resources, UC Davis, One Shields Ave, Davis, CA 95616, USA Soil K varied regionally and may be related to irrigation water and soil parent material. The critical level for Kext (currently 60 mg K kg−1) may need to be revised based on our findings, as there was evidence of K deficiencies above this concentration. Keywords Rice · Potassium · Indices · Nutrient balances · Deficiency Introduction In rice (Oryza sativa L.), potassium (K) has many essential functions, including osmoregulation, enzyme activation, and stomatal function (DeDatta and Mikkelsen 1985). When soils are deficient in K, plant biomass and yields are reduced, disease incidence increases (Linquist et al. 2008; Williams and Smith 2001), and there is a greater potential for lodging (Kono and Takahashi 1961). Plant demand for K is comparable to nitrogen demand in terms of total seasonal uptake; and on average, 17 kg K are taken up by the crop for every ton of grain yield (Dobermann and Fairhurst 2000; DeDatta and Mikkelsen 1985). However, unlike nitrogen, which is mostly in the rice grain at harvest, only 15–20% of the K is in the grain; the remainder is in the straw. Therefore, grain harvest has a relatively small effect on soil K balances; while straw management can have a large effect on soil K balances and the sustainability of the system. Fertilization with K Vol.: (0123456789) 13 Nutr Cycl Agroecosyst Vol:. (1234567890) 13 Nutr Cycl Agroecosyst ◂Fig. 1  Map showing locations of fields in the Sacramento Val- ley. Numbers refer to those in Table 1. The different shade of circles indicate if fields (mean of all samples from the field) have low soil extractable K (Kext < 120 mg kg−1) or low K saturation (Ksat < 1.6%) and if the soil is a fixing or non-K fixing soil. In all cases where fertilizer K was applied, flag-leaf K values were > 1.2%. At sites that did not receive fertilizer K, at the following sites flag-leaf K values were < 1.2% in at least one of the field checks tested:16, 41, 43, 49, 52 and 53 has not been common in many rice-producing regions around the world. However, without K fertilization and with increasing yields, K balances will be negatively affected and K deficiencies are expected to become more common (Dobermann et al. 1996a). In the soil, K is present as: (1) soil solution K, (2) exchangeable K, (3) fixed K in interlayer minerals and, (4) matrix K in rocks and minerals (Barber 1995). Solution and exchangeable K are readily plant-available, but make up only a small fraction of the total K (DeDatta and Mikkelsen 1985; Bell et al. 2021a). Potassium fixation occurs when K is held in highly charged sites in the interlayer region of some layer-silicate minerals, such as vermiculite, smectite and mica. As granitic parent materials weather, primary mica minerals weather into secondary minerals, such as vermiculite and smectite. These minerals often further weather into kaolinite and gibbsite (O’Geen et al. 2008). Minerals vary in their capacity to fix K, with vermiculite having high fixation potential, while kaolinite and gibbsite have little to no fixation potential (Bouabid et al. 1991). The Sacramento Valley, where most of California rice is grown, lies just north of the San Joaquin Valley (Fig. 1). The Cascade and the Sierra Nevada ranges border the Sacramento Valley on the east, and the Coast Range borders on the west. The San Joaquin Valley is bordered on the east by the Sierra Nevada and on the west by the Coast Range. Coast Range-derived soils often have high Kext and little or no K-fixation, while the Sierra Nevada-derived soils containing granitic alluvium generally fix K (Murashkina et al. 2007a). In the San Joaquin Valley, K fertilizer requirements are higher in K-fixing soils than in non-fixing soils (Cassman et al. 1990). However, K-fixation and K fertility requirements have not been studied in the Sacramento Valley. Mikkelsen and Hunziker (1971) reported more K-deficient soils on the eastern side of the Sacramento Valley, but this has not been linked to K-fixation in these soils. In California, rice yields are among the highest in the world. Rice yields have been increasing in California and have averaged 9.5 t ha−1 over the past 10 years (USDA 2021). Not all farmers apply K fertilizer, but for those that do, average rates are 28 to 40 kg K ha−1 (Hartley and van Kessel 2003; Williams 2010). Historically, rice straw was burned following harvest; however, in the 1990s, straw burning was restricted and most farmers began incorporating rice straw during the winter, then flooding fields to accelerate rice straw decomposition (Linquist et al. 2006). In these systems, straw K is thought to be conserved within the field. Assuming an average yield and that there is 2.5 kg K per ton of grain (Dobermann and Fairhurst 2000), 24 kg K ha−1 is removed in the grain at harvest. Thus, for those farmers applying K fertilizer and assuming the only K lost is via grain K removal, the K is balanced in the system. However, many California farmers do not apply K fertilizer, similar to farmers globally. As for other farmers around the world, farmers may not apply K because soils are high in clay and there are plenty of reserves, the irrigation water may contain K, and there are no visible deficiencies of K (Dobermann et al. 1996a). At question is (...truncated)