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PurposeThe aims of this study were to investigate the links between potassium (K) uptake by crops and soil K, exchangeable calcium (Ca2+), magnesium (Mg2+), and aluminum (Al3+) when using lime in acidic soil in southern China.Materials and methodsSoil samples of three treatments (chemical NP fertilizers, NPK, and NPK plus straw (NPKS)) were collected from a 26-year field experiment (0–20 cm) and then a rhizobox experiment was conducted with seven lime application rates (0–2.26 g kg−1). We investigated the soil exchangeable K+, Ca2+, Mg2+, and Al3+ and non-exchangeable K (NEK) in the rhizosphere soil (RS) and non-rhizosphere soils (NRS), and K uptake by crops.Results and discussionAs lime addition rates increased, the average concentration of exchangeable K (EK) in RS under NPK and NPKS treatments decreased to 46.5 mg kg−1 and 70.4 mg kg−1 for maize and wheat, respectively. In treatments with lime application, the NEK concentration was higher in RS and NRS compared with the no-lime in NP treatment but was lower in RS in treatments with K fertilizer input (NPK and NPKS). The K uptake by crops under lime application significantly (p < 0.05) increased by 37.6% to 155.1% compared with the no-lime treatments. Lime application significantly increased soil exchangeable Ca2+ (42.9 to 255.7%) and decreased exchangeable Al3+ (23.7 to 86.6%). According to structural equation modeling, lime indirectly influenced K uptake by crops through its effects on soil exchangeable Ca2++Mg2+ and Al3+, EK, and NEK, which accounted for up to 39% (RS) and 46% (NRS) of the variation in the K uptake by crops. Lime directly and negatively affected EK and NEK in NRS but had no direct effects on EK and NEK in RS.ConclusionsOur results suggested that lime-induced K uptake by crops was mediated by K+, Ca2+, and Al3+, and that lime application resulted in higher soil K availability.

PurposeHuge amounts of radiocesium, radiostrontium, and fission products were released into the atmosphere during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Therefore, it is necessary to determine the distribution coefficient of Cs and Sr in the soil-water system around FDNPP from the viewpoint of their migration.Materials and methodsThe determination of sorption coefficient Kd(S) as well as desorption coefficient Kd(D) for Cs and Sr has been carried out in the present study using the laboratory batch method. In this experiment, stable Cs and Sr were used for sorption on contaminated Fukushima soil samples and groundwater collected in proximity to the soil sample sites. Different soil parameters were measured to understand their effect on the sorption and desorption processes. Desorption experiments were carried out on some selected contaminated soil samples.Results and discussionKd(S)-Cs and Kd(S)-Sr varied from 65 to 2100 L/kg and 15 to 130 L/kg, respectively. Kd(D)-Cs and Kd(D)-Sr varied between 75–2500 and 10–120 L/kg, respectively. High values of sorption coefficients for Cs indicate sorption capacity of soils for Cs is more than Sr. For Cs, Kd(D) was higher than Kd(S) whereas for Sr, Kd(S) was either equal to or higher than Kd(D). A moderate Pearson’s correlation of (Kd) Cs and Sr with exchangeable cations (Al, K, Mg, and Na) supported that ion exchange sorption mechanism is significant. There is enhanced Cs sorption compared to Sr due to the presence of biotite, kaolinite and smectite minerals resulting in high mobility of Sr in the Fukushima environment.ConclusionsWe concluded retention capacity of Fukushima soils for Cs is moderately stronger than Sr, which supports Sr is more mobile in the environment.

In soil, potassium (K) is present as structural K, non-exchangeable K (Kne) and exchangeable K (Ke). Exchangeable K is considered available to plants, but exudates from plant roots and microbes can dissolve Kne and make it available. Some grasses used as cover crops are particularly efficient in releasing Kne. In this work, we assessed the effects of early K application to ruzigrass in a sandy soil on soil K forms, K uptake by cotton and soil K balance. Potassium was applied (i) to ruzigrass; (ii) half to ruzigrass and half to cotton; (iii) on cotton grown on ruzigrass; and (iv) on cotton in the absence of ruzigrass, or K was not applied (v) in the presence of ruzigrass and (vi) in absence or ruzigrass. The accumulation of K by ruzigrass ranged from 40 to 250 kg ha −1 , and about half of it was washed out of the plant residues by 20 days after desiccation. Ke was lowest throughout the soil profile in the absence of K fertilization regardless of ruzigrass. By contrast, in the 0–10 cm soil layer, Kne was 88% higher with unfertilized ruzigrass than in the absence of both K fertilization and ruzigrass. K fertilization of cotton increased Ke to a depth of 40–60 cm when grown on ruzigrass. The K balance was most negative in the absence of K fertilization and ruzigrass (0 K), but a similar negative balance of 116 kg ha −1 of K was observed when ruzigrass was grown without K fertilization. Conversely, K application to ruzigrass resulted in a positive Ke balance. The release of K from ruzigrass residues delayed the decrease in soil Kne and increased soil Ke 40 days after desiccation. In conclusion, applying K to ruzigrass grown before cotton is an effective strategy for ensuring the release of K to cotton, improving the soil K balance, and avoiding K depletion.

Rapid land use changes have been observed in recent years in central Ethiopia. The shift from natural ecosystem to artificial ecosystem is the main direction of change. Therefore, this study was initiated to assess the effects of land use types on selected soil properties in Meja watershed, central highlands of Ethiopia. The randomized complete block design, including three adjacent land use types as treatments with three replications and two soil depths (0–15 and 15–30 cm), was applied in this study. There were significant differences in some soil properties among the three land use types. Lower soil pH and electric conductivity were observed in cultivated land soils than Eucalyptus woodlots soils. This has indicated the worsening soil conditions due to the shift from Eucalyptus woodlots to cultivated land. Less decomposition rate of the Eucalyptus leaves and debris collection for fuel could result in lowest soil organic carbon at the upper layer of Eucalyptus woodlot soils. However, the highest soil organic carbon at the lower layer was observed in Eucalyptus woodlot soils. The presence of highest soil potassium, cation exchange capacity, and exchangeable potassium in cultivated land soil was related to application of artificial fertilizers. Grassland soils have highest exchangeable sodium at the lower layer while highest soil carbon and sum cations at the upper layer, which can be related to the grass root biomass return and less surface runoff on grassland. There was the highest exchangeable sodium percentage on Eucalyptus woodlot soils at the upper layer; it can be due to the less surface nutrient movement and growth characteristics of the tree. The soils in cultivated land was shifted to more acidic and less electric conductivity.This shift can lead to soil quality deterioration that affects the productivity of the soils in the future.Nutrient leaching, application of artificial fertilizer, soil erosion, and continuous farming have affected the soil properties in cultivated land. The presence of highest exchangeable sodium percentage and lowest sum of cations at the upper layer of soil in Eucalyptus woodlot should be noted for management and decision makers. The previous negative speculations on Eucalyptus woodlots which can be related with the soil texture, soil moisture, bulk density, total nitrogen, exchangeable magnesium, calcium, and available sulfur should be avoided because there were no significant differences observed among the three land use types in the study area. The study recommends further studies on the effects of Eucalyptus on soil properties by comparing among different ages and species of Eucalyptus. Finally, planting of Eucalyptus on central highlands of Ethiopia should be supported by land use management decision.

Inadequate or lack of prudent soil fertility management by cocoa farmers leads to nutrient depletion in cocoa production fields. The objective of this study was to assess current soil fertility status of cocoa farms from six cocoa growing regions in Ghana and to derive an integrated soil quality index (SQI). Composite soil samples from 0 to 30 cm depth were collected from 100 selected farms covering the six cocoa regions. Soil pH, %C, %N, total and available P, cation exchange capacity (CEC), and exchangeable cations (Ca, Mg, K) were measured. These parameters were analyzed using principal component analysis, normalized, and integrated into a weighted-additive SQI. Soil pH of majority (59.0%) of the farms was within 5.6–7.2, suitable for cocoa production. Available soil-P in most (82%) of the farms was < 20 mg kg−1. Soil quality in most farms was generally low, with an average SQI of 0.41 ± 0.14. Soil quality in Western region farms was relatively high, followed by farms in Brong Ahafo and Volta regions. Farms in Eastern, Central and Ashanti regions had the least soil quality. Soil pH, CEC and available P showed great influence on SQI. Given the latter observation, diagnostic yield response experiments should be conducted, which include: application of locally generated liming materials, organic residues and agro-mineral base fertilizers such as phosphate rock and dolomite.

The soil non-exchangeable potassium (K) pool contributes significantly to meeting crop K requirements. The objective of this study was to determine wheat and rice grain yield responses to different concentrations of sodium tetraphenylboron (NaTPB) extractable non-exchangeable K in soils. A field experiment was conducted over a period of 4 years using three K application strategies in soils with high (JY) and low (GD) levels of non-exchangeable K. In both soils, rice yield was unaffected by K application during the 4-year study period. However, in GD soil, wheat was unable to produce grains without K additions (0 K) during the fourth wheat season. In JY soil, wheat grain yield decreased only in the 0 K (by 11%) compared with the recommended K application during the fourth wheat season. Different responses in wheat between the two soils indicated that NaTPB-non-exchangeable K better represented the soil K supplying capacity than it did exchangeable K. Lower amounts of non-exchangeable K extracted by NaTPB in GD soil were mainly due to lower amounts extracted during the 0–5 s and 5–10 min time periods. Straw retention alone resulted in negative K balances, with 100 kg K ha −1  yr −1 in JY soil and 95 kg ha −1  yr −1  in GD soil. In conclusion, recommended K application combined with NaTPB-K monitoring would be useful for sustaining crop yield and soil K fertility among different soils in rice–wheat cropping systems.

Heterogeneity in soil fertility in these smallholder systems is caused by both inherent soil‐landscape and human‐induced variability across farms differing in resources and practices. Interventions to address the problem of poor soil fertility in Africa must be designed to target such diversity and spatially heterogeneity. Data on soil management and soil fertility from six districts in Kenya and Uganda were gathered to understand the determinants of soil heterogeneity within farms. Analysis of the variance of soil fertility indicators across 250 randomly selected farms (i.e., 2607 fields), using a mixed model that considered site, sampling frame, farm type, and field as random terms, revealed that the variation in soil organic C (6.5–27.7 g kg−1), total N (0.6–3.0 g kg−1), and available P (0.9–27 mg kg−1) was mostly related to differences in the inherent properties of the soils across sites (50 to 60% of total variance). Exchangeable K+ (0.1–1.1 cmol(+) kg−1), Ca2+ (1.5–14.5 cmol(+) kg−1), Mg2+ (0.6–3.7 cmol(+) kg−1), and pH (5.1–6.9) exhibited larger residual variability associated with field‐to‐field differences within farms (30 to 50%). Soil fertility indicators decreased significantly with increasing distance from the homesteads. When this variable was included in the model, the unexplained residual variances—associated with soil heterogeneity within farms—were 38% for soil C; 32% for total N; 49% for available P; 56, 49, and 38% for exchangeable K+, Ca2+ and Mg2+, respectively; and 49% for the pH. In allocating nutrient resources, farmers prioritized fields they perceived as most fertile, reinforcing soil heterogeneity. Categorization of fields within a farm with respect to distance from the homestead, and soil fertility classes as perceived by farmers, were identified as entry points to target soil fertility recommendations to easily recognizable, distinct entities.

The amendment of two agricultural soils with two biochars derived from the slow pyrolysis of papermill waste was assessed in a glasshouse study. Characterisation of both biochars revealed high surface area (115 m2 g-1) and zones of calcium mineral agglomeration. The biochars differed slightly in their liming values (33% and 29%), and carbon content (50% and 52%). Molar H/C ratios of 0.3 in the biochars suggested aromatic stability. At application rates of 10 t ha-1 in a ferrosol both biochars significantly increased pH, CEC, exchangeable Ca and total C, while in a calcarosol both biochars increased C while biochar 2 also increased exchangeable K. Biochars reduced Al availability (ca. 2 cmol (+) kg-1 to <0.1 cmol (+) kg-1) in the ferrosol. The analysis of biomass production revealed a range of responses, due to both biochar characteristics and soil type. Both biochars significantly increased N uptake in wheat grown in fertiliser amended ferrosol. Concomitant increase in biomass production (250% times that of control) therefore suggested improved fertiliser use efficiency. Likewise, biochar amendment significantly increased biomass in soybean and radish in the ferrosol with fertiliser. The calcarosol amended with fertiliser and biochar however gave varied crop responses: Increased soybean biomass, but reduced wheat and radish biomass. No significant effects of biochar were shown in the absence of fertiliser for wheat and soybean, while radish biomass increased significantly. Earthworms showed preference for biochar-amended ferrosol over control soils with no significant difference recorded for the calcarosol. The results from this work demonstrate that the agronomic benefits of papermill biochars have to be verified for different soil types and crops.

The remediation of opencast bauxite mines in the natural forests of Indonesia is difficult. We have investigated and contrasted the chemical characteristics of soils from natural forests and mining sites and their effects on plant growth. The soil pH, total carbon (C), nitrogen (N) and available phosphorus (P) concentrations, cation exchange capacity, C/N ratio, and exchangeable K, Na, Mg, Ca, Fe, and Ni concentrations were determined. Falcataria moluccana and Albizia saman were then grown in these soils for 15 weeks, and their shoot heights, shoot dry weights, and root dry weights determined. The post bauxite mining soils’ N, C, and available P concentrations and exchangeable Ca, Mg, and Na concentrations decreased by 75, 75.7, 15.7, 92, 100, and 52%, respectively, in comparison with the natural forest soils. The shoot and root dry weights of F. moluccana when grown in the post bauxite mining soils were also lower than those from the natural forest soils. However, there was no difference in the shoot and root dry weights of A. saman when grown in the two soil types. The results suggest that opencast mining decreases the soil fertility, which in turn inhibits the initial growth of tree seedlings, and reduces the carbon stock in the land.

Soil salinity may damage crop production. Besides proper management of irrigation water, salinity reduction can be achieved through soil amendment. The objectives of this study were to evaluate the effects of rice husk biochar and compost amendments on alleviation of salinity and rice growth. Field experiments were conducted at two salt-affected paddy rice fields located in distinct sites for five continuous crops. Treatments, with four replicates, consisted of continuous three rice crops per year (RRR), two rice crops rotated with fallow in spring–summer crop (FRR), FRR plus compost at 3 Mg ha−1 crop−1 (FRR + Comp), and biochar at 10 Mg ha−1 crop−1 (FRR + BC). Salt contents and hydraulic properties of soils, plant biomass, and plant uptake of cations were investigated. Soil bulk density (BD), exchangeable sodium (Na+), and exchangeable sodium percentage (ESP) were reduced remarkably by biochar application. Biochar application significantly increased other soil properties including total porosity, saturated hydraulic conductivity (Ksat), soluble and exchangeable potassium (K+), K+/Na+ ratio, available P, and total C. Compost application also improved BD, total porosity, and available P, but not exchangeable Na+ and ESP. Total aboveground biomass of rice showed a trend of FRR + BC > FRR + Comp > FRR > RRR. Relatively higher K+ uptake and lower Na+ uptake in rice straw in FRR + BC resulted in a significant two times higher K+/Na+ ratio over other treatments. Our results highlight that biochar amendment is a beneficial option for reducing ESP and providing available K+ and P under salinity-affected P-deficient conditions, hence improving straw biomass.