Soil Exchangeable Potassium Research Articles

Fixed or mixed? Variation in tree functional types and vegetation structure in a forest-savanna ecotone in West Africa

AbstractWe analysed thirty-five 400-m2 plots encompassing forest, savanna and intermediate vegetation types in an ecotonal area in Ghana, West Africa. Across all plots, fire frequency was over a period of 15 years relatively uniform (once in 2–4 years). Although woodlands were dominated by species typically associated with savanna-type formations, and with forest formations dominated by species usually associated with closed canopies, these associations were non-obligatory and with a discrete non-specialized species grouping also identified. Across all plots, crown area index, stem basal area and above-ground biomass were positively associated with higher soil exchangeable potassium and silt contents: this supporting recent suggestions of interplays between potassium and soil water storage potential as a significant influence on tropical vegetation structure. We also found an average NDVI cover increase of ~0.15% year−1 (1984–2011) with plots dominated by non-specialized species increasing more than those dominated by either forest- or savanna-affiliated species. Our results challenge the traditional view of a simple forest vs. savanna dichotomy controlled by fire, and with our newly identified third non-specialized species grouping also potentially important in understanding ecotonal responses to climate change.

Influence of the Fertilization System on Fertility Indicators of Sod-Podzolic Heavy Loamy Soil in the Pre-Urals

The effect of long-term usage of various fertilization systems (organic, mineral, and organic-mineral) on the agrochemical indicators of sod-podzolic heavy loamy soil and the productivity of crops of eight-field crop rotation has been studied. Fertilization systems with high saturation (manure 20 t/ha per year, NPK in equivalents of manure 20 t/ha per year, and manure 10 t/ha per year + NPK in equivalents of manure) provided a significant increase in soil humus content (from 1.97 to 2.23–2.50%), mobile phosphorus (by 120–145 mg/kg), and exchangeable potassium (by 105–163 mg/kg) as well as increase in total, mineral, and hydrolyzable nitrogen content (by 200–360, 1.3–2.3, and 53–65 mg/kg, respectively). Cattle manure contributes to a decrease in hydrolytic acidity from 2.3 to 1.5–1.8 and to an increase in the amount of exchange bases from 18.2 to 20.8–21.9 mmol/100 g of soil. NPK treatment (in equivalents of manure 20 t/ha per year) leads to an increase in the hydrolytic acidity by 1.0 and to a decrease in the total exchangeable bases by 1.1 mmol/100 g. The maximum productivity of arable land (3800 fodder units per ha) has been obtained under fertilization systems NPK equivalent to manure 20 t/ha per year and manure 10 t/ha per year + NPK in equivalents of manure.

Variations in radioactive cesium accumulation in wheat germplasm from fields affected by the 2011 Fukushima nuclear power plant accident

Decreasing the transfer of radioactive cesium (RCs) from soil to crops has been important since the deposition of RCs in agricultural soil owing to the Fukushima nuclear power plant accident of 2011. We investigated the genotypic variation in RCs accumulation in 234 and 198 hexaploid wheat (Triticum spp.) varieties in an affected field in 2012 and 2013, respectively. The effects of soil exchangeable potassium (ExK) content to RCs accumulation in wheat varieties were also evaluated. A test field showed fourfold differences in soil ExK contents based on location, and the wheat varieties grown in areas with lower soil ExK contents tended to have higher grain RCs concentrations. RCs concentrations of shoots, when corrected by the soil ExK content, were positively significantly correlated between years, and RCs concentrations of shoots were significantly correlated with the grain RCs concentration corrected by the soil ExK content. These results indicated that there were genotypic variations in RCs accumulation. The grain to shoot ratio of RCs also showed significant genotypic variation. Wheat varieties with low RCs accumulations were identified. They could contribute to the research and breeding of low RCs accumulating wheat and to agricultural production in the area affected by RCs deposition.

Critical Value of Soil Potassium for Potato Crops in Volcanic Soils

The critical value of soil exchangeable potassium (K) (mg K kg−1) is a valuable tool for an efficient K fertilization management in potato production systems. The aim of the present study was to determine the critical value of soil exchangeable K for potato crops grown in different environments and differing availabilities of initial exchangeable K. The data used in this study were taken from 34 experiments on K fertilization conducted in southern Chile from 1977 to 2017 by the National Potato Center at the Instituto de Investigaciones Agropecuarias (INIA). Yield responses to K fertilization rates were assessed with linear-plateau and Mitscherlich models in order to determine the critical soil exchangeable K across environments. Across experiments, the average fresh tuber yield ranged between 18 and 91 Mg ha−1. Fresh tuber yields decreased by up to 70% when no K fertilization was applied. Yield reduction was concentrated around 25% in response to K deficiency. Relative yields were described as significant by both linear-plateau and Mitscherlich models. However, relative yields were better described by the linear-plateau model (p < 0.01, R2 = 0.62; SEE = 0.11). The critical soil exchangeable K value identified with the linear-plateau model was 224 mg K kg−1. This critical K value will be useful for potato farmers that produce their crops in volcanic soils, such as Andisols. Moreover, this critical K value will help to increase K use efficiency through better K fertilization management strategies aimed at building and/or maintaining K levels in soils.

The role of oil palm biomass recycling on soil health in oil palm plantations

Oil palm cultivation produces a massive amount of biomass (e.g., empty fruit bunches (EFB), frond and trunk) which could be recycled directly in the plantation to maintain/improve the quality of soils. The impact of this biomass recycling, i.e., EFB and frond, - in term of chemical, physical and biological characteristics, will be analyzed. The fresh application of the EFB could alternate most of the soil parameters in line with the kinetics of the decomposition of the EFB and the release of nutrients. For example, the pH of the soil after the EFB application was higher during more than 18 months compared to the initial situation. Soil exchangeable potassium increased dramatically within a few days after EFB spreading. Frond recycling, at harvesting and pruning, modifies the chemical and physical characteristics of soils whether they were applied on heaps between palms in dedicated inter-rows, or spread on harvesting paths where they could reduce run-off and erosion. The systematic distribution of fronds in inter-rows reduced rainwater run-off by more than 30%, even on 5% gentle slopes. Subsequently, soil loss through erosion was reduced by 65% depending on the slope intensity of the terrain. Consequently, the loss of nutrients was considerably reduced, resulting in higher fertilizer efficiency. Similar measurements have been done when applying fresh EFB to the soil. The impact on soil physical fertility, i.e., rainwater infiltration rate and subsequently soil humidity are improved. We have also recorded a reduction of the soil resistance to penetration, as well as an improvement of the soil aggregate stability. Several representative parameters of soil biological activity, i.e., soil fauna feeding activity using bait-lamina test system and earthworm’ population showed the positive impact of EFB applications as well as frond spreading in inter-rows.

Chemical attributes of soil under cassava wastewater application in Marandugrass cultivation

ABSTRACT There is a worldwide concern regarding the management of agroindustrial residues, involving sustainable practices that contribute to taking advantage of the residues as inputs in productive processes, allowing greater efficiency in the integration of agricultural activities and mitigating their adverse effects on the soil. Therefore, the objective of this study was to assess the effects of application of cassava wastewater on the chemical attributes of the soil cultivated with Brachiaria brizantha cv. Marandu. The experimental design was in randomized blocks with five treatments (0, 15, 30, 60 and 120 m³ ha-1 of cassava wastewater) and four repetitions. To characterize soil chemical attributes soil samples were collected at depths 0 to 10 and 10 to 20 cm, for determination of the concentrations of soil organic matter, available phosphorus, exchangeable potassium, sodium, calcium and magnesium before and after cassava wastewater application were determined. The application of cassava wastewater increases available phosphorus and exchangeable potassium concentrations, decreases exchangeable calcium, magnesium and organic matter contents of the soil cultivated with Marandu grass. Cassava wastewater can be used as organic fertilizer for pastures of Marandu grass with doses of up to 120 m³ ha-1.

Towards the partial resumption of agriculture with buckwheat cultivation in fields physically decontaminated of radioactive cesium after the nuclear power plant accident in 2011: a case study in Yamakiya District, Fukushima

ABSTRACT Yamakiya District in the town of Kawamata, Fukushima Prefecture, was evacuated after the nuclear accident at the Tokyo Electric Power Company’s Fukushima Dai-ichi nuclear power plant in 2011. Since then, nuclear decontamination procedures have been applied to the surrounding environment, including agricultural fields. The decontamination procedure for agricultural fields consists of the removal of radiation-contaminated surface soil, followed by soil dressing and plowing. However, radioactive cesium (RCs) remains in the soil even after decontamination. In this study, we investigated the effect of applying nitrogen, potassium fertilizers, and cattle manure compost on buckwheat growth and the concentration of RCs in the grain of buckwheat cultivated in a decontaminated field from 2014 to 2016. Applications of potassium fertilizer and cattle manure compost increased the soil exchangeable potassium content and decreased the RCs concentration in the grain of buckwheat cultivated in the decontaminated field. Before the cultivation of the first buckwheat crop, the RCs concentration in soil varied widely and there were ‘hot spots’ with high RCs concentrations because of insufficient mixing of the original and the dressed soils. Therefore, soil had to be adequately mixed to avoid producing grain with a high RCs concentration. Buckwheat grew better when supplied with more nitrogen fertilizer than the conventional amount at the first cultivation, indicating that the dressed soil had low fertility. We also monitored buckwheat cultivation by local farmers in decontaminated fields from 2015 to 2017. By using potassium fertilizer, the farmers produced buckwheat grain with low RCs concentrations from 2015 to 2017.

A statistical model for estimating the radiocesium transfer factor from soil to brown rice using the soil exchangeable potassium content

To reduce radiocesium uptake by rice, large amounts of potassium fertilizer have been applied to paddy fields contaminated by radiocesium released from the Fukushima Dai-ichi Nuclear Power Plant owned by the Tokyo Electric Power Company. The Fukushima Prefectural Government recommended maintenance of the soil exchangeable K content up to 200 mg K kg−1 before conventional fertilization in rice production. We constructed an equation to predict the transfer factor from soil to brown rice using the soil exchangeable K content. This equation was then used to calculate the appropriate soil exchangeable K content, which ensures a low risk (5%) of brown rice exceeding the standard limit (100 Bq kg−1 for grains) established in 2012. The equations were constructed using field data obtained by an investigation (measurement of the 137Cs concentrations in soil and brown rice and measurement of the soil exchangeable K content at harvest) that was performed from 2012 to 2015 in 321 paddy fields distributed all over Fukushima Prefecture. We found that the stochastic fluctuation of the transfer factor approximately follows a lognormal distribution under the given environmental conditions. Four factors are considered in predicting the logarithmic quantity of the transfer factor: (1) the linear influence of the logarithm of the exchangeable K content in soil, (2) the non-linear influence of the logarithm of the exchangeable K content in soil, (3) three districts in the Fukushima Prefecture and (4) the year. The linear model of the logarithm of exchangeable K content in soil was adopted by the RD criterion, which indicates the absolute goodness of models for prediction. The predictive ability of the model increased by 29% after including the logarithm of the exchangeable K content in soil (factor 1), while the predictive ability further increased by 10% after including spatial and temporal information (factors 3 and 4). The validity of the exchangeable K content recommended by the Fukushima Prefectural Government was re-examined using the proposed equations, which indicated that the conventional recommendation was appropriate at 2012 but is not fully appropriate under the current situation in which the radiocesium concentration in soil has decreased.

Improvement of a simplified method for measuring exchangeable soil potassium by using a compact potassium ion meter for improvement its accuracy

Improvement of a simplified method for measuring exchangeable soil potassium by using a compact potassium ion meter for improvement its accuracy

Dynamics of mobile potassium in typical black soil in short-term crop rotations

Changes in the content of the exchange potassium of the soil in the system of short-rotation crop rotations depending on the saturation and placement of crops in them was shown their intensification (fertilizer system).&#x0D; Quantitative changes in exchangeable potassium in soil during vegetation of plants hanges depend not only on their consumption by plants, but also on the intake of potassium from organic compounds into the soil solution. In particular, direct application of 20-40 t / ha manure together with N60-100P40-100K60-100 for row crops, provides a high content of exchangeable potassium: after the cultivation of corn - 110-140 mg / kg, sugar beet - 140-200, sunflower - 130-220 mg / kg. The lowest content (70-80 mg / kg) of exchangeable potassium was observed in all fields of control crop rotation (without fertilization), where potassium of the soil and root residues of the cultivated crops served as a source of potassium for plants. Also in most fields after harvesting barley spring (100-120 mg / kg), for applying under the culture of N60P40K60.

Potential Use of King Coconut Husk as a Nutrient Source for Organic Coconut Cultivation

King coconut husk (KCH) is a waste material from nut water processing industry which has no identified economic value, rather causing environmental problems. The KCH was used to develop a nutrient supplement material (NSM) by controlled combustion inside a kiln. Among the three categories of moist, semi-dry and dry coconut husk used for combustion, semi-dry KCH was found to be the best for processing in terms of time taken for the processing and ease of handling. The product was analyzed for nutrient availability and found that it contained considerable amounts of macro and micro nutrients. The developed NSM was then tested under field condition to investigate the potential for it to be used as a source of nutrient in coconut cultivation. The treatments were: T1- Recommended straight fertilizer (N, P, K) for coconut, T2- NSM was added as a source of K while other nutrients were same as in T1, and T3 - K source supplied from sulfate of potash while other fertilizers were similar to T1. Three months after treatment application, representative soil samples were extracted and tested for soil pH, electrical conductivity and soil exchangeable potassium levels. According to the results, the product contained considerable amounts of macro nutrients including N (2.1 - 2.4%) and K (8.8 - 13.1%), and micro nutrients including Zn (1350 - 1522 ppm) and Cu (61.2 - 62.5 ppm). The K content of NSM was around three times higher than the K content of other locally available organic manure. This indicates the potential of the product as a source of nutrient. Even though the pH of developed NSM product was higher (10.6), after application this product into soil, there was no significant difference among treatments. The NSM incorporated treatment showed significantly higher soil K content compared to other treatments which indicates its potential to be used as a source of K with organic manure for young coconut.

A Newly Identified Role of the Deciduous Forest Floor in the Timing of Green‐Up

AbstractPlant phenology studies rarely consider controlling factors other than air temperature. We evaluate here the potential significance of physical and chemical properties of soil (edaphic factors) as additional important controls on phenology. More specifically, we investigate causal connections between satellite‐observed green‐up dates of small forest watersheds and soil properties in the Adirondack Mountains of New York, USA. Contrary to the findings of previous studies, where edaphic controls of spring phenology were found to be marginal, our analyses show that at least three factors manifest themselves as significant controls of seasonal patterns of variation in vegetated land surfaces observed from remote sensing: (1) thickness of the forest floor, (2) concentration of exchangeable soil potassium, and (3) soil acidity. For example, a thick forest floor appears to delay the onset of green‐up. Watersheds with elevated concentrations of potassium are associated with early surface greening. We also found that trees growing in strongly acidified watersheds demonstrate delayed green‐up dates. Overall, our work demonstrates that, at the scale of small forest watersheds, edaphic factors can explain a significant percentage of the observed spatial variation in land surface phenology that is comparable to the percentage that can be explained by climatic and landscape factors. We conclude that physical and chemical properties of forest soil play important roles in forest ecosystems as modulators of climatic drivers controlling the rate of spring soil warming and the transition of trees out of winter dormancy.

Optimization of nitrogen and potassium nutrition to improve yield and yield parameters of irrigated almond (Prunus dulcis (Mill.) D. A. webb)

Abstract An experiment was conducted to evaluate the effect of nitrogen (N) and potassium (K) fertilization rates and fertilizer sources on almond yield and yield related parameters- fruit and kernel weight, number of fruits per tree, crackout percentage and leaf nutrient status by individually monitoring 768 trees. The experiment was carried out between 2008 and 2012 with four rates (140, 224, 309 and 392 kg N ha−1) and two sources (UAN and CAN) of N and three rates (112, 224 and 336 kg K ha−1) and sources (SOP + KTS, SOP and KCl) of K. Nitrogen fertilizer rate had a significant effect on yield in the second through the fourth year of the experiment. Tree yield was maximized at 18.5 kg and 23.7 kg kernel per tree in 2010 and 2011 season respectively when July leaf N was in the range 2.4–2.5% corresponding to an N application rate of 309 kg N ha−1 and there was no increment in yield above 2.5% leaf N. Source of N had no significant effect on yield response. Potassium fertilization rate had no significant effect on yield while K sources had significant effect in 2010 only. Increasing N application resulted in lighter fruit, and kernel weight decreased with increasing N application under moderate yield conditions, and increased under high yield conditions. Yield increase with increasing N application was due to an increase in number of fruits and increased crackout percentage. Leaf K above 1% did not increase yield and there was no consistent effect of K supply and K source on yield parameters. There was a strong relationship between total yield and number of fruits per tree, which increased with increasing N application. Crackout percentage was also positively correlated to kernel yield. Nitrogen and potassium fertilization rate should be based on expected yield and tree N and K status. For a well productive mature orchard, N application of 309 kg ha−1 with either UAN or CAN can meet crop N needs. K fertilization should consider K contribution from soil. Under condition of 100–150 mg kg−1 soil exchangeable potassium, K application of 112 kg ha−1 with any K fertilizer source can satisfy crop K demand.

Spatial downscaling of soil prediction models based on weighted generalized additive models in smallholder farm settings.

Digital soil mapping (DSM) is gaining momentum as a technique to help smallholder farmers secure soil security and food security in developing regions. However, communications of the digital soil mapping information between diverse audiences become problematic due to the inconsistent scale of DSM information. Spatial downscaling can make use of accessible soil information at relatively coarse spatial resolution to provide valuable soil information at relatively fine spatial resolution. The objective of this research was to disaggregate the coarse spatial resolution soil exchangeable potassium (Kex) and soil total nitrogen (TN) base map into fine spatial resolution soil downscaled map using weighted generalized additive models (GAMs) in two smallholder villages in South India. By incorporating fine spatial resolution spectral indices in the downscaling process, the soil downscaled maps not only conserve the spatial information of coarse spatial resolution soil maps but also depict the spatial details of soil properties at fine spatial resolution. The results of this study demonstrated difference between the fine spatial resolution downscaled maps and fine spatial resolution base maps is smaller than the difference between coarse spatial resolution base maps and fine spatial resolution base maps. The appropriate and economical strategy to promote the DSM technique in smallholder farms is to develop the relatively coarse spatial resolution soil prediction maps or utilize available coarse spatial resolution soil maps at the regional scale and to disaggregate these maps to the fine spatial resolution downscaled soil maps at farm scale.

Effect of Non-flooded Plastic Film Mulching Cultivation for Rice in Southeast China

The effects of non-flooded plastic film mulching cultivation (PM) and polymer-coated urea (PCU) on rice yield, soil properties, and weed diversity were investigated in experimental plots of rice monoculture in Lanxi, China. The combination of PM and PCU increased rice yield. Compared with traditional flooded cultivation, under PM, soil pH remained higher, but decreased soil organic matter, total nitrogen, available phosphorus, and exchangeable potassium in the 0- to 10-cm soil layer. Soil fertility influenced winter weed communities, with hairy bittercress, Asian mazus, and shortawn foxtail being the most abundant species. Multivariate analysis indicated that changes in the winter weed species diversity were primarily due to exchangeable potassium. PCU had no significant influence on weed diversity, while plots without nitrogen fertilizer had higher spring-germinating weed density.

Effect of soil exchangeable potassium content on cesium absorption and partitioning in buckwheat grown in a radioactive cesium-contaminated field

The effect of soil exchangeable (plant-available) potassium (ExK) content on cesium (Cs) absorption and translocation in buckwheat was evaluated in a field contaminated with radioactive Cs (134Cs and 137Cs, RCs) in 2013. The RCs concentration in buckwheat was significantly positively correlated with the naturally occurring stable Cs (133Cs, SCs) concentration, and was lower at higher soil ExK content. The RCs and SCs were actively absorbed by buckwheat until the flowering stage. The soil ExK content was significantly negatively correlated with soil exchangeable RCs and SCs (ExRCs and ExSCs) concentrations. Greater RCs and SCs absorption by buckwheat in soils with low ExK contents was mainly due to higher soil ExRCs and ExSCs concentrations. Reproductive organs showed the largest differences in SCs concentration between low-ExK and high-ExK plots. The root–shoot and shoot–reproductive organs translocations of SCs markedly decreased with increasing soil ExK content. In the root–shoot and shoot–reproductive organs translocations, the discrimination of SCs and K decreased with decreasing soil ExK content. Our main findings were as follows: (1) because RCs are mainly taken up at the earlier growth stage, potassium should be applied as a basal fertilizer to decrease the RCs concentration in buckwheat; (2) lower soil ExK content led to higher soil ExRCs concentrations, resulting in greater RCs absorption by buckwheat; (3) the high Cs absorption and translocation and weaker discrimination between Cs and K in low ExK content soil may be due to the expression of K transporter(s) with weak discrimination between Cs and K.

Evaluating the effect of remote sensing image spatial resolution on soil exchangeable potassium prediction models in smallholder farm settings

Major end users of Digital Soil Mapping (DSM) such as policy makers and agricultural extension workers are faced with choosing the appropriate remote sensing data. The objective of this research is to analyze the spatial resolution effects of different remote sensing images on soil prediction models in two smallholder farms in Southern India called Kothapally (Telangana State), and Masuti (Karnataka State), and provide empirical guidelines to choose the appropriate remote sensing images in DSM. Bayesian kriging (BK) was utilized to characterize the spatial pattern of exchangeable potassium (Kex) in the topsoil (0–15 cm) at different spatial resolutions by incorporating spectral indices from Landsat 8 (30 m), RapidEye (5 m), and WorldView-2/GeoEye-1/Pleiades-1A images (2 m). Some spectral indices such as band reflectances, band ratios, Crust Index and Atmospherically Resistant Vegetation Index from multiple images showed relatively strong correlations with soil Kex in two study areas. The research also suggested that fine spatial resolution WorldView-2/GeoEye-1/Pleiades-1A-based and RapidEye-based soil prediction models would not necessarily have higher prediction performance than coarse spatial resolution Landsat 8-based soil prediction models. The end users of DSM in smallholder farm settings need select the appropriate spectral indices and consider different factors such as the spatial resolution, band width, spectral resolution, temporal frequency, cost, and processing time of different remote sensing images. Overall, remote sensing-based Digital Soil Mapping has potential to be promoted to smallholder farm settings all over the world and help smallholder farmers implement sustainable and field-specific soil nutrient management scheme.

Incorporation of satellite remote sensing pan-sharpened imagery into digital soil prediction and mapping models to characterize soil property variability in small agricultural fields

Soil prediction models based on spectral indices from some multispectral images are too coarse to characterize spatial pattern of soil properties in small and heterogeneous agricultural lands. Image pan-sharpening has seldom been utilized in Digital Soil Mapping research before. This research aimed to analyze the effects of pan-sharpened (PAN) remote sensing spectral indices on soil prediction models in smallholder farm settings. This research fused the panchromatic band and multispectral (MS) bands of WorldView-2, GeoEye-1, and Landsat 8 images in a village in Southern India by Brovey, Gram-Schmidt and Intensity-Hue-Saturation methods. Random Forest was utilized to develop soil total nitrogen (TN) and soil exchangeable potassium (Kex) prediction models by incorporating multiple spectral indices from the PAN and MS images. Overall, our results showed that PAN remote sensing spectral indices have similar spectral characteristics with soil TN and Kex as MS remote sensing spectral indices. There is no soil prediction model incorporating the specific type of pan-sharpened spectral indices always had the strongest prediction capability of soil TN and Kex. The incorporation of pan-sharpened remote sensing spectral data not only increased the spatial resolution of the soil prediction maps, but also enhanced the prediction accuracy of soil prediction models.Small farms with limited footprint, fragmented ownership and diverse crop cycle should benefit greatly from the pan-sharpened high spatial resolution imagery for soil property mapping. Our results show that multiple high and medium resolution images can be used to map soil properties suggesting the possibility of an improvement in the maps’ update frequency. Additionally, the results should benefit the large agricultural community through the reduction of routine soil sampling cost and improved prediction accuracy.

The effects of straw or straw-derived gasification biochar applications on soil quality and crop productivity: A farm case study

Thermal gasification of straw is a highly efficient technology that produces bioenergy and gasification biochar that can be used as a soil amendment, thereby returning non-renewable nutrients and stable carbon, and securing soil quality and crop productivity.A Danish on-farm field study investigated the impact of traditional straw incorporation vs. straw removal for thermal gasification bioenergy production and the application of straw gasification biochar (GB) on soil quality and crop production. Two rates of GB were applied over three successive years in which the field was cropped with winter wheat (Triticum aestivum L.), winter oilseed rape (Brassica napus L.) and winter wheat, respectively, to assess the potential effects on the soil carbon pool, soil microorganisms, earthworms, soil chemical properties and crop yields.The application of GB did not increase the soil organic carbon content significantly and had no effect on crop yields. The application of straw and GB had a positive effect on the populations of bacteria and protists, but no effect on earthworms. The high rate of GB increased soil exchangeable potassium content and soil pH indicating its potassium bioavailability and liming properties.These results suggest, that recycling GB into agricultural soils has the potential to be developed into a system combining bioenergy generation from agricultural residues and crop production, while maintaining soil quality. However, future studies should be undertaken to assess its long-term effects and to identify the optimum balance between straw removal and biochar application rate.

Organic Wheat Farming Improves Grain Zinc Concentration.

Zinc (Zn) nutrition is of key relevance in India, as a large fraction of the population suffers from Zn malnutrition and many soils contain little plant available Zn. In this study we compared organic and conventional wheat cropping systems with respect to DTPA (diethylene triamine pentaacetic acid)-extractable Zn as a proxy for plant available Zn, yield, and grain Zn concentration. We analyzed soil and wheat grain samples from 30 organic and 30 conventional farms in Madhya Pradesh (central India), and conducted farmer interviews to elucidate sociological and management variables. Total and DTPA-extractable soil Zn concentrations and grain yield (3400 kg ha-1) did not differ between the two farming systems, but with 32 and 28 mg kg-1 respectively, grain Zn concentrations were higher on organic than conventional farms (t = -2.2, p = 0.03). Furthermore, multiple linear regression analyses revealed that (a) total soil zinc and sulfur concentrations were the best predictors of DTPA-extractable soil Zn, (b) Olsen phosphate taken as a proxy for available soil phosphorus, exchangeable soil potassium, harvest date, training of farmers in nutrient management, and soil silt content were the best predictors of yield, and (c) yield, Olsen phosphate, grain nitrogen, farmyard manure availability, and the type of cropping system were the best predictors of grain Zn concentration. Results suggested that organic wheat contained more Zn despite same yield level due to higher nutrient efficiency. Higher nutrient efficiency was also seen in organic wheat for P, N and S. The study thus suggests that appropriate farm management can lead to competitive yield and improved Zn concentration in wheat grains on organic farms.