K-use Efficiency Research Articles

Optimization of phosphorus and potassium use efficiency of rice (Oryza sativa L) under different flood depths within the Everglades Agricultural Area

Rice cultivation in South Florida, especially within crop rotation systems, presents a promising avenue for mitigating phosphorus (P) levels in drainage water by optimizing nutrient absorption across varying flooding conditions. This study aimed to assess the impacts of different flooding depths on rice growth and nutrient efficiency while exploring the interrelationships among these factors. Conducted over a two-year period, the field study involved planting a single rice variety (Diamond: 95 kg ha−1, long-grain, short-season) at four distinct flooding depths (5, 10, 15, and 20 cm) without fertilizer application. Results revealed minimal effects of flooding depths on root and shoot length or dry matter accumulation. Additionally, concentrations of total P and potassium (K) in both shoot and root tissues remained consistent across the different flooding depths. Despite the absence of P and K fertilizer inputs, no significant changes were observed in P use efficiency (PUE), K use efficiency (KUE), or water use efficiency (WUE). Cultivating rice under optimal flood depths of 5 cm within the Everglades Agricultural Area (EAA) demonstrated potential for conserving water and essential nutrients such as P and K. These findings highlight the feasibility of rice cultivation in fertile soils as a means to decrease nutrient (P and K) concentrations in drainage water, thereby promoting sustainable agricultural practices in the region.

Partial root zone irrigation and K application improves summer maize production and salt resistance in saline soil

Irrigation patterns and K fertilization are the key measures used to improve the salt tolerance of crops in saline land. A pot experiment was carried out to assess the effects of partial root-zone irrigation and K fertilization on maize in saline land. For the study parameters, we used a split plot design with three irrigation treatments (conventional irrigation (CI), fixed root-zone irrigation (FRI) and alternate root-zone irrigation (ARI)) and two K application rates (0 (K0) and 120 (K1) kg K2O ha−1). Compared with the CI treatment, the FRI and ARI treatments reduced the transpiration rate (Tr) and MDA content but increased the root length density (RLD), root surface density (RSD), root volume density (RVD), root dry weight density (RDWD), proline content, plant K/Na ratio, photosynthetic rate (Pn), yield, water use efficiency (WUE) and K use efficiency (KUE). Compared with the FRI treatment, the ARI treatment increased RLD, RSD, RVD, RDWD, the Tr, the proline content, the plant K/Na ratio and the Pn but decreased the MDA content; these factors increased yield, WUE and KUE. K application decreased the MDA content; improved root growth; and increased the stomatal conductance, Tr, proline content, Pn, yield and WUE. Of all the treatments, the ARI-K1 treatment maximized RLD, RSD, RVD, RDWD, the Pn and yield while minimizing the MDA content. Therefore, ARI combined with K application can maximize resistance to salt stress and osmotic stress, delay senescence, and improve photosynthesis, yield and WUE.

Delayed Sowing Can Improve Potassium Utilization Efficiency and Grain Potassium Concentration in Winter Wheat

Economic consumption and environmental impacts due to potassium (K) inputs in agriculture are gaining increasing attention. It is urgent to improve K use efficiency (KUE) for agricultural development. Delayed sowing has been shown to maintain grain yield in winter wheat. Still, there needs to be more information regarding the effect of sowing date on crop K status evaluated by the K nutrition index (KNI), KUE, K uptake efficiency (UPE), K utilization efficiency (UTE), and grain K concentration (GKC). Here, we assessed Shannong23 and Tainong18 winter wheat cultivars with three sowing date treatments composed of 26 September (early sowing), 8 October (normal sowing), and 22 October (late sowing) in the 2021–2022 and 2022–2023 growing seasons. The influences of sowing date on the KNI, tillering, grain yield formation, KUE, UPE, UTE, K transport, and GKC were examined. Our study indicated that late sowing in winter wheat was an almost optimal K nutritional situation, whereas early and normal sowing were under situations of excess K. As sowing was delayed, aboveground K uptake (AGK), UPE, and spike number per unit area decreased; UTE and grain number per spike increased; and grain yield and KUE were unchanged. A positive correlation between KNI and UPE and spike number per unit area and a negative correlation between KNI and UTE and grain number per spike were found, whereas no significant correlation between KNI and KUE was observed. Late sowing promoted K transport from pre-anthesis accumulation in vegetative organs to grain, resulting in a higher GKC, which could lead to high grain quality and K recovery. Therefore, late sowing winter wheat can use K more efficiently and increase GKC, implying that delayed sowing can reduce K input, favoring sustainable agriculture development.

Identification of Modern High-Yield Soybean Genotypes for Potassium-Use Efficiency in Sandy Soil of the Brazilian Cerrado

Soybean is the main leguminous crop in Brazil, mostly grown in tropical soils with low potassium (K) availability. Therefore, the identification of new genotypes with efficient K uptake and utilization in environments with low exchangeable K content is an economically viable alternative to maximize crop yield in Brazil. A study was conducted to investigate the response of 25 modern high-yield soybean genotypes for K-use efficiency in a sandy tropical soil of the Brazilian Cerrado. Treatments were distributed in a completely randomized design in a 2 × 25 factorial scheme: two levels of K fertilization [20 mg K dm−3 (low level) or 200 mg K dm−3 (high level)] and 25 soybean genotypes with three replicates. Plant morphological traits, leaf K, and crop production components were measured. Based on grain production data, K-use efficiency (KUE) and response efficiency (RE) to K fertilization were calculated. Leaf area, shoot dry matter, pod number per plant, 1000-grain weight, and grain yield were the crop characteristics most limited by low soil K availability. The soybean genotypes “TMG7061 IPRO”, “BMX Bônus IPRO”, “RK6719 IPRO”, and “RK8317 IPRO” were classified as efficient in the use of soil K and are the most suitable genotypes to be cultivated in agricultural soils with low K availability. The genotypes “98R35 IPRO”, “HO Maracaí IPRO”, “BMX Bônus IPRO”, and “RK7518 IPRO” were classified as responsive to K fertilization and are the most recommended genotypes for cultivation in agricultural areas with the application of high K fertilizer rates. The genotype “BMX Bônus IPRO” simultaneously combines characteristics of K-use efficiency and response to K fertilization and hence can be grown in both K-deficient and optimal soils.

Functional Dissection of the Physiological Traits Promoting Durum Wheat (Triticum durum Desf.) Tolerance to Drought Stress

In Tunisia's arid and semi-arid lands, drought stress remains the most critical factor limiting agricultural production due to low and irregular precipitation. The situation is even more difficult because of the scarcity of underground water for irrigation and the climate change that has intensified and expanded the aridity. One of the most efficient and sustainable approaches to mitigating drought stress is exploring genotypic variability to screen tolerant genotypes and identify useful tolerance traits. To this end, six Tunisian wheat genotypes (Triticum durum Desf.) were cultivated in the field, under a greenhouse and natural light, to be studied for their differential tolerance to drought stress. Many morpho-physiological and biochemical traits were analyzed, and interrelationships were established. Depending on the genotypes, drought stress significantly decreased plant growth, chlorophyll biosynthesis, and photosynthesis; stimulated osmolyte accumulation and disturbed water relations. The most tolerant genotypes (salim and karim) accumulated more potassium (K) and proline in their shoots, allowing them to maintain better tissue hydration and physiological functioning. The osmotic adjustment (OA), in which potassium and proline play a key role, determines wheat tolerance to drought stress. The calculated drought index (DI), drought susceptible index (DSI), drought tolerance index (DTI), K use efficiency (KUE), and water use efficiency (WUE) discriminated the studied genotypes and confirmed the relative tolerance of salim and karim.

Morphophysiological and transcriptome analysis reveal that reprogramming of metabolism, phytohormones and root development pathways governs the potassium (K+) deficiency response in two contrasting chickpea cultivars.

Potassium (K+) is an essential macronutrient for plant growth and development. K+ deficiency hampers important plant processes, such as enzyme activation, protein synthesis, photosynthesis and stomata movement. Molecular mechanism of K+ deficiency tolerance has been partly understood in model plants Arabidopsis, but its knowledge in legume crop chickpea is missing. Here, morphophysiological analysis revealed that among five high yielding desi chickpea cultivars, PUSA362 shows stunted plant growth, reduced primary root growth and low K+ content under K+ deficiency. In contrast, PUSA372 had negligible effect on these parameters suggesting that PUSA362 is K+ deficiency sensitive and PUSA372 is a K+ deficiency tolerant chickpea cultivar. RNA-seq based transcriptome analysis under K+ deficiency revealed a total of 820 differential expressed genes (DEG's) in PUSA362 and 682 DEGs in PUSA372. These DEGs belongs to different functional categories, such as plant metabolism, signal transduction components, transcription factors, ion/nutrient transporters, phytohormone biosynthesis and signalling, and root growth and development. RNA-seq expression of randomly selected 16 DEGs was validated by RT-qPCR. Out of 16 genes, 13 showed expression pattern similar to RNA-seq expression, that verified the RNA-seq expression data. Total 258 and 159 genes were exclusively up-regulated, and 386 and 347 genes were down-regulated, respectively in PUSA362 and PUSA372. 14 DEGs showed contrasting expression pattern as they were up-regulated in PUSA362 and down-regulated in PUSA372. These include somatic embryogenesis receptor-like kinase 1, thaumatin-like protein, ferric reduction oxidase 2 and transcription factor bHLH93. Nine genes which were down-regulated in PUSA362 found to be up-regulated in PUSA372, including glutathione S-transferase like, putative calmodulin-like 19, high affinity nitrate transporter 2.4 and ERF17-like protein. Some important carbohydrate metabolism related genes, like fructose-1,6-bisphosphatase and sucrose synthase, and root growth related Expansin gene were exclusively down-regulated, while an ethylene biosynthesis gene 1-aminocyclopropane-1-carboxylate oxidase 1 (ACO1) was up-regulated in PUSA362. Interplay of these and several other genes related to hormones (auxin, cytokinin, GA etc.), signal transduction components (like CBLs and CIPKs), ion transporters and transcription factors might underlie the contrasting response of two chickpea cultivars to K+ deficiency. In future, some of these key genes will be utilized in genetic engineering and breeding programs for developing chickpea cultivars with improved K+ use efficiency (KUE) and K+ deficiency tolerance traits.

Introduction of Bacillus thuringiensis (Bt) gene does not reduce potassium use efficiency of Bt transgenic cotton (Gossypium hirsutum L.)

BackgroundPotassium (K) deficiency has become a common field production problem following the widespread adoption of Bacillus thuringiensis (Bt) transgenic cotton (Gossypium hirsutum L.) worldwide. The purpose of this study was to clarify whether the introduction of Bt gene directly reduces the K-use efficiency of cotton to induce K deficiency.ResultsThe cotton variety, Jihe 321 (wild type, WT) and its two Bt (Cry1Ac)-transgenic overexpression lines (OE-29317, OE-29312) were studied in field with low soil-test K+ (47.8 mg·kg−1). In the field with low soil-test K+, only OE-29317 had less biomass and K+ accumulation than the WT at some growth stages. Both Bt lines produced similar or even greater seed cotton yield than WT in the field. When the Bt gene (~ 70%) in OE-29317 and OE-29312 plants was silenced by virus-induced gene silencing (VIGS), the VIGS-Bt plants did not produce more biomass than VIGS-green fluorescent protein (control) plants.ConclusionsThe introduction of Bt gene did not necessarily hinder the K use efficiency of the cotton lines under this study.

Rice Potassium Transporter OsHAK8 Mediates K+ Uptake and Translocation in Response to Low K+ Stress.

Potassium (K+) levels in the soil often limit plant growth and development. As a result, crop production largely relies on the heavy use of chemical fertilizers, presenting a challenging problem in sustainable agriculture. To breed crops with higher K+-use efficiency (KUE), we must learn how K+ is acquired from the soil by the root system and transported to the rest of the plant through K+ transporters. In this study, we identified the function of the rice K+ transporter OsHAK8, whose expression level is downregulated in response to low-K+ stress. When OsHAK8 was disrupted by CRISPR/Cas9-mediated mutagenesis, Oshak8 mutant plants showed stunted growth, especially under low-K+ conditions. Ion content analyses indicated that K+ uptake and root-to-shoot K+ transport were significantly impaired in Oshak8 mutants under low-K+ conditions. As the OsHAK8 gene was broadly expressed in different cell types in the roots and its protein was targeted to the plasma membrane, we propose that OsHAK8 serves as a major transporter for both uptake and root-to-shoot translocation in rice plants.

English

Improving potassium (K) use efficiency (KUE) is beneficial for the sustainable production of cereal crops. In this study, the effects of K input level on its uptake and agronomic trait of the winter wheat under deficit irrigation were investigated in K deprivation responses, using two cultivars contrasting (low-K tolerant cultivar Kenong 9204 and K deprivation sensitive one Jimai 120). Under sufficient-K treatment (K180, SK), the two cultivars showed similar K contents, and K accumulation, biomass, photosynthetic parameters in upper expanded leaves, including yield components. Under deficient-K (K60, DK) condition, both cultivars showed varied behaviors of the K-associated traits, physiological parameters, growth and agronomic traits; however, better response was observed in Kenong 9204 than Jimai 120. These results suggested the essential roles of low-K tolerant cultivars under the K-saving management together with deficit irrigation. Two genes of the potassium transporter (HAK) family, TaHAK3 and TaHAK5, showed expression of significantly upregulated upon K deprivation, with much more transcripts shown in the K-deprived Kenong 9204 plants than Jimai 120 ones. Transgene analysis on the HAK genes validated their positive roles in modulating the K accumulation and biomass production of plants under low-K condition. These results indicated that distinct HAK family genes are transcriptionally regulated underlying K deprivation signaling and contribute to plant K uptake and biomass production under low-K conditions. This study suggested the drastically genetic variation on K uptake and biomass production across winter wheat cultivars treated by K- and water-saving conditions, associated with transcription efficiency of the distinct HAK genes which modulate K uptake, growth and development of plants. © 2021 Friends Science Publishers

Diverse feedstock’s biochars as supplementary K fertilizer improves maize productivity, soil organic C and KUE under semiarid climate

The contemporary exhaustive agriculture has led to drastic reductions in soil potassium (K) status because of constant soil K mining by crops without sufficient recharge through external K inputs. Therefore, substituting and/or supplementing K through alternative sources has great prospects in developing countries like Pakistan, where imported K fertilizers are comparatively expensive. This two-year field study reports the effects of alternative sources of K as farmyard manure (FYM), sugarcane bagasse and woodchip, and their biochars (B) i.e. FYM-B, bagasse-B and woodchip-B on soil fertility, K availability, K use efficiency (KUE), soil organic carbon (SOC) and maize productivity in calcareous soil of the semiarid northern region of Pakistan. Alternative sources of K and their biochars were applied along mineral K fertilizer as muriate of potash (KCl) at 60 kg ha−1 rate in a randomized complete block design. Results showed that FYM–B significantly increased plant height, grains per cob and 1000-grain weight. The FYM–B increased grain yield by 6.5, 37.2, and 87.0% when compared with woodchip–B, chemical fertilizer and control treatments, respectively. Similarly, FYM–B and woodchip–B significantly increased SOC and soil available K contents as compared with the rest of the treatments. Grain K contents and KUE were generally higher in biochar than their feedstock treatments during both years. However, FYM–B resulted in significantly higher KUE compared to the other K sources and their biochars during both years. The biological and grain yields showed significant positive correlations with soil K and SOC contents. Our study concluded that FYM and FYM-B can be applied as alternative and/or supplementary K sources along woodchip-B and bagasse-B to improve maize productivity, KUE and SOC contents in nutrient poor soil. However, economic feasibility of such practices is required to be priorly investigated on long-term basis.

Integrated Application of K and Zn as an Avenue to Promote Sugar Beet Yield, Industrial Sugar Quality, and K-Use Efficiency in a Salty Semi-Arid Agro-Ecosystem

Salinity combined with a deficiency of potassium (K) and zinc (Zn) negatively affect sugar beet yield and quality. A two-year (2017/18–2018/19) field trial was undertaken to investigate the mediating role of soil-applied K [120 (K120) and 180 (K180) kg ha−1] and foliar-applied Zn [0 (Zn0), 150 (Zn150), and 300 (Zn300) ppm] in alleviating salt-stress (8.60 dS m−1) based on sugar beet morpho-physiological responses, sugar yield and quality, and K-use efficiency in the BTS 301 and Kawemira cultivars. Application of K180 × Zn300 was more effective and resulted in 23.39 and 37.78% higher root yield (RY) and pure sugar yield (PSY), respectively, compared to control (K120 × Zn0). It also enhanced sucrose, pure sugar (PS), and purity but decreased impurities (α-amino N, K, and Na), alkalinity index, and sugar loss. However, the K120 × Zn300 recorded higher K-use efficiency. PSY correlated positively (r = 0.776 **, 0.629 **, 0.602 **, 0.549 **, and 0.513 **) with RY, root fresh weight (RFW), top yield, PS, and root diameter, respectively. The stepwise and path-coefficient analysis demonstrated that RY, PS, and RFW were the most influential PSY-affected attributes. Integration of K180 + Zn300 can correct K and Zn deficiencies in the soil and mitigate salt-stress effects via improving sugar beet growth, yield and quality, and K-use efficiency.

Investigating the effect of Aspergillus niger inoculated press mud (biofertilizer) on the potential of enhancing maize (Zea mays. L) yield, potassium use efficiency and potassium agronomic efficiency

Globally field application of mineral potassium (K) fertilizer has grown, followed by reduced K use efficiency (KUE) and K agronomic efficiency (KAE) which ultimately leads to environmental pollution and economic loss. The soils of Pakistan have a low K level due to a higher proportion is present in an unavailable form. The objective of the current study was to isolate efficient plant growth-promoting fungus to sustainably manage huge burden of sugar industry waste press mud into a productive biofertilizer. K from biofertilizer was then evaluated in different treatments for maize biological yield, grain yield, harvest index (HI), K uptake in different maize parts, KUE and KAE in comparison to mineral fertilizer (MF). The efficiency of treatment was measured on higher KUE and KAE. In-vitro studies revealed that A. niger PM-4 was found to solubilize phosphate (389 ug/ml) and zinc (115 ug/ml) from insoluble tri-calcium phosphate and zinc oxide, respectively, at a wider temperature and pH range. The strain was also found to inhibit the production of aflatoxins and its inoculation into press mud produced non-phytotoxic and mature biofertilizer with germination index 96.5%. Bio-augmentation of press mud with A. niger shortens maturity period with improved nutrient contents. Higher grain yield and harvest index of maize were achieved with a higher amount of incorporated K from mineral and biofertilizer T5(100%Org+50%MF) than any other treatment. However, higher KUE and KAE were found in the following order: T6 > T5 > T2 > T3 > T4 > T1, demonstrating the integrated and balanced use of K from mineral and biofertilizer without threatening the environment.

Identification of QTLs associated with potassium use efficiency and underlying candidate genes by whole-genome resequencing of two parental lines in Brassica napus

Breeding crops that acquire and/or utilize potassium (K) more effectively could reduce the use of K fertilizers. Sixteen traits affecting K use efficiency (KUE) at the seedling stage were investigated in a B. napus double haploid population grown at an optimal K supply (OK) and a low K supply (LK) in a hydroponic culture system. In total, 50 and 62 QTLs associated with these traits were identified at OK and LK, respectively. A total of 25 orthologues of 23 Arabidopsis genes regulating K transport were identified in the confidence intervals of nine QTLs impacting shoot dry weight at LK, and 22 of these showed variations in coding sequences and/or exhibited significant differences in mRNA abundances in roots at LK between the two parental lines. This study provided insights to the genetic basis of KUE in B. napus, which will accelerate the breeding of K-efficient rapeseed cultivars by marker-assisted selection.

Potassium fertilization for white oat and maize in integrated crop‐livestock system under no‐tillage

AbstractIntegrated crop‐livestock systems (ICLS) are diversified agroecosystems characterized by the rotation, succession or mixtures of agricultural, livestock or forestry activities, in no‐tillage systems. In ICLS with trees, the tree modifies the light and water availability, and might generate root competition for nutrients, like potassium (K). The study aims to evaluate dry matter (DM) and macronutrients accumulation in white oat, DM and grain yield of maize, and the K use efficiency (KUE) by these crops cultivated in an ICLS with eucalyptus. The experimental design was a randomized block in a split‐plot design with three replications. Plots consisted of four cultivation positions (CP) between the tree rows, where CP1 (0 to 4 m distance) refers to a position close to the trees; CP2 (4 to 8 m distance) and CP4 (12 to 16 m distance) corresponds to two intermediate positions between rows; and CP3 (8 to 12 m distance) corresponds to a central position between rows. In subplots, four potassium oxide (K2O) annual doses were assigned, with potassium chloride being applied on the surface, where each rate was half the rate applied at sowing of each crop. DM and macronutrients accumulation in white oat shoot decreased due to eucalyptus shadow (64.5% light restriction). Responses of maize DM and grain yield to K2O addition were different among CPs, possibly owing to different light patterns. No changes in the maize yield were observed with K2O application in CP1 and CP2. However, for other positions, quadratic responses in grain yield were observed. In ICLS with eucalyptus in a subtropical region of Brazil, the reduction of K fertilization led to lower yields in white oat and maize. As KUE was high in plots with low K rate, the production cost in ICLS with trees may be decreased if massive production is not required.

Enhancing potassium content in leaves and stems improves drought tolerance of eucalyptus clones.

Eucalyptus are widely planted in regions with low rainfall, occasioning frequent drought stresses. To alleviate the stress-induced effects on plants growing in these environments, soil fertilization with potassium (K) may affect drought-adaptive plant mechanisms, notably on tropical soils with low K availability. This work aimed to evaluate the K dynamic nutrition in eucalyptus in response to soil-K and -water availabilities, correlating the K-nutritional status with the physiological responses of contrasting eucalyptus clones to drought tolerance. A complete randomized design was used to investigate the effects of three water regimes (well-watered, moderate water deficit, and severe water deficit) and two K soil supplies (sufficient and low K) on growth and physiological responses of two elite eucalyptus clones: "VM01" (Eucalyptus urophylla × camaldulensis) and "AEC 0144" (E. urophylla). Results depicted that the K-well-nourished E. urophylla × camaldulensis clone under severe water deficit maintained shoot biomass accumulation by upregulating the K-content in leaves and stems, gas exchange, water-use efficiency (WUEI ), leaf water potential (Ψw), and chlorophyll a fluorescence parameters, compared to E. urophylla clone. Meanwhile, E. urophylla with a severe water deficit showed a decreased of K content in leaves and stem, as well as a reduction in the accumulation of dry mass. Therefore, the K-use efficiency and the apparent electron transport rate through photosystem II were positively correlated in plants grown in low K, indicating the importance of K in maintaining leaf photochemical processes. In conclusion, management strategy should seek to enhance K-nutrition to optimize water-use efficiencies and photosynthesis.

Global identification and characterization of miRNA family members responsive to potassium deprivation in wheat (Triticum aestivum L.)

Potassium (K) is essential for plant growth and stress responses. MicroRNAs (miRNAs) are involved in adaptation to nutrient deprivation through modulating gene expression. Here, we identified the miRNAs responsive to K deficiency in Triticum aestivum based on high-throughput small RNA sequencing analyses. Eighty-nine miRNAs, including 68 previously reported ones and 21 novel ones, displayed differential expression under K deficiency. In Gene Ontology and Kyoto Encyclopedia and Genome analyses, the putative target genes of the differentially expressed miRNAs were categorized into functional groups associated with ADP-binding activity, secondary metabolic pathways, and biosynthesis and metabolism. Functional characterization of tae-miR408, an miRNA significantly down-regulated under K deficiency, revealed its important role in mediating low-K tolerance. Compared with wild type, transgenic tobacco lines overexpressing tae-miR408 showed significantly improved K uptake, biomass, photosynthesis, and reactive oxygen species scavenging under K deficiency. These results show that distinct miRNAs function in the plant response to K deficiency through regulating target genes involved in energy metabolism and various secondary metabolic pathways. Our findings shed light on the plant response to K deficiency mediated by miRNAs in T. aestivum. Distinct miRNAs, such as tae-miR408, are valuable targets for generating crop varieties with improved K-use efficiency.

Straw return increases crop grain yields and K-use efficiency under a maize-rice cropping system

Straw return is an effective way to improve crop grain yield and potassium (K) use efficiency by increasing soil K content. However, the effects of straw return on soil K supplying capacity, replacement of K fertilizer, and K-use efficiency under maize (Zea mays L.)–rice (Oryza sativa L.) cropping systems are little studied. A two-year field experiment was conducted to determine the physiological determinants of K-use efficiency under straw return with four K fertilization rates. Sr33 (straw returned plus 33% of K fertilizer applied) and Sr67 (straw returned plus 67% of K fertilizer applied) increased annual crop yields by 1.5% and 3.2% and increased agronomic K-use efficiency by respectively 2.9 and 1.3-fold on average in the two years, compared with the conventional practice S0K100 (no straw returned plus normal amounts of K fertilizer applied). The Sr33 and Sr67 treatments resulted in significantly greater equilibrium K concentration ratios (CR0K) and specifically exchangeable K (KX) values according to quantity/intensity (Q/I) relationship analyses, indicating improvement of the potential soil K supply capacity. However, the Sr67 better maintained the soil exchangeable K level and K balance. The results suggested that K released from maize and rice straw can replace about half of chemical K fertilizer, depending on the available K content in maize–rice cropping system production.

Overexpression of V-type H+ pyrophosphatase gene EdVP1 from Elymus dahuricus increases yield and potassium uptake of transgenic wheat under low potassium conditions

Lack of potassium in soil limits crop yield. Increasing yield and conserving potassium ore requires improving K use efficiency (KUE). Many genes influence KUE in plants, but it is not clear how these genes function in the field. We identified the V-type H+-pyrophosphatase gene EdVP1 from Elymus dahurica. Gene expression analysis showed that EdVP1 was induced by low potassium stress. Protein subcellular localization analysis demonstrated that EdVP1 localized on the plasma membrane. We overexpressed EdVP1 in two wheat varieties and conducted K tolerance experiments across years. Yield per plant, grain number per spike, plant height, and K uptake of four transgenic wheat lines increased significantly compared with WT; results from two consecutive years showed that EdVP1 significantly increased yield and KUE of transgenic wheat. Pot experiments showed that transgenic plants had significantly longer shoots and roots, and higher K accumulation in shoots and roots and H+-PPase activity in shoots than WT under low K. A fluidity assay of potassium ion in EdVP1 transgenic plant roots showed that potassium ion influx and H+ outflow in transgenic plants were higher than WT. Overexpressing EdVP1 significantly improved yield and KUE of transgenic wheat and was related to higher K uptake capacity in root.

Foliar K application to rainfed wheat in a soil testing high K as an option to improve K use efficiency, grain yield and yield components

Granular application of potassium (K) in soils testing high is generally not recommended. However, the effect of foliar K on rainfed wheat (Triticum aestivum L.) under these soil conditions is largely unknown. The objective of this work was to identify the effect of K fertilizer on K use efficiency (KUE), grain yield and yield components of wheat. The data were collected until 2017 in an ongoing trial established in 2007 with eight treatments; two granular K rates (0 and 50 kg K ha−1); two foliar N rates (0 and 3 kg N ha−1); and two foliar K rates (0 and 3 kg K ha−1) in a split-split plot arrangement. Treatments were applied to the same plots each season. Treatment with foliar K resulted in the highest KUE response but the effect size varied according to the accumulated precipitation during the reproductive stage. On average, KUE was enhanced in crop seasons with water constrains (<179 mm) during the growth period but the converse was true as the amount of precipitation increased. In contrast, granular K had no effect on KUE irrespective of precipitation conditions. Application of foliar K increased grain yield as compared to granular K from 2988 to 3089 kg ha−1. This enhancement was attributed to an increased number of grains per head. Therefore, foliar K application to wheat is suitable in a soil testing high K to enhance KUE and grain yield, overall in crop seasons with water constrains.

Long-term effects of controlled-release potassium chloride on soil available potassium, nutrient absorption and yield of maize plants

Controlled-release potassium chloride (CRK) has been shown to improve potassium (K) use efficiency (KUE) and crop yields. However, its widespread use has limited by its high manufacturing costs. To help address this problem and to find the best techniques for using CRK, we mixed it with traditional potassium chloride (KCl) in 1:1 ratios in a five-year field test to find the resulting KUE, bleeding sap, yields, and economic returns of maize (Zea mays L.). There were six treatments subjected to varying K fertilization: full-dose, traditional KCl; full-dose, CRK; reduced-dose, CRK; full-dose, mixed CRK and traditional KCl; reduced-dose, mixed CRK and traditional KCl; and the control, which had no added K fertilizer. Applying high dose, mixed CRK and traditional KCl and high dose, CRK to maize significantly increased grain yields 14.0% and 7.2%, respectively, compared with the traditional KCl treatment during 2014–2018. When the K was provided at the low rate (reduced by one-third), the low dose, mixed CRK and traditional KCl and low dose, CRK treatments led to the same yields as the traditional KCl treatment. However, crude starch contents of the mixed CRK and traditional KCl and CRK treatments each were significantly increased compared with the traditional KCl treatment in 2018. Mean KUE increased 30.5%–56.5% for mixed CRK and traditional KCl treatments, compared with traditional KCl during 2016–2018. Mean net profits from the high dose, mixed CRK and traditional KCl treatment significantly increased 18.9%, when K was provided by the lower rate of mixed CRK and traditional KCl led to the same net profit, compared with traditional KCl treatment from the 2016–2018 years. During the milky maturity stage of maize plants, bleeding sap in the high dose, mixed CRK and traditional KCl treatment were 47.5% and 23.4% lower than from the traditional KCl and high dose, CRK treatments, respectively. Meanwhile, the high dose, mixed CRK and traditional KCl and high dose, CRK treatments significantly increased soil available K levels compared with the traditional KCl treatment, hence, meeting the nutrient demands of maize plants during their later growth stages. The exchangeable Ca2+ levels within the soil near the surface was also maximized by the long-term application of mixed CRK and traditional KCl treatments. Hence, applying mixed CRK and traditional KCl fertilizers were recommended for maintaining continued nutrient absorption soil fertility, sustainable increases in crops yields and for maximizing net profits.