Short-term effects of organo-mineral enriched biochar fertiliser on ginger yield and nutrient cycling

Purpose

Biochar has agronomic potential but currently is too expensive for widespread adoption. New methodologies are emerging to reduce the cost such as enriching biochar with nutrients that match crops and soil requirements. However, the effects of biochar-based fertilisers on plant yield and soil nutrient availability have not been widely examined. This study investigated the effects of a novel organo-mineral biochar fertiliser in comparison to organic and commercial biochar fertiliser on ginger (Zingiber officinale Canton).

Materials and methods

There were four treatments: (1) commercial organic fertiliser (5 t ha^?1), as the control; (2) commercial biochar-based fertiliser (5 t ha^?1); (3) organo-mineral biochar fertiliser at low rate (3 t ha^?1); and (4) organo-mineral biochar fertiliser at high rate (7.5 t ha^?1). A replicated pot trial was established with black dermosol soil and ten replicate pots for each treatment. Ginger was planted and grown for 30 weeks. Plant growth, biomass, foliar nutrients and water extractable soil nutrients including phosphorus (P), potassium (K) and calcium (Ca) were examined.

Results and discussion

High rate organo-mineral biochar fertiliser increased soil P and K availability at week 30 (harvest) after planting, compared to all other treatments and low rate organo-mineral biochar fertiliser performed similarly to the organic control for P and K. High rate organo-mineral biochar fertiliser increased total foliar nutrient content at week 30 in P, K and Ca compared to commercial biochar fertiliser. High rate organo-mineral biochar fertiliser improved the commercial value of ginger (+?36%) due to a shift in the proportion of higher grade rhizomes. Low rate organo-mineral biochar fertiliser plants displayed similar yield, total dry and aboveground biomass to commercial organic fertiliser. Commercial biochar fertiliser had significantly lower biomass measures compared with other treatments as the rate applied had lower nutrient concentrations.

Conclusions

Our results show organo-mineral biochar fertilisers could be substituted for commercial organic fertilisers at low rates to maintain similar yield or applied at high rates to increase commercial value where economically feasible.

     

Efficiency of soil-applied 67Zn-enriched fertiliser across three consecutive crops

A very small amount of applied zinc (Zn) is taken up by crops, resulting in low recovery by plants. Adding elemental sulphur to zinc oxide (ZnO) fertiliser could improve Zn solubilisation and exert a higher residual effect on crops than soluble Zn sources. We produced an isotopically labelled Zn-elemental sulphur fertiliser and evaluated its performance in comparison to traditional Zn sources during sequential crop cultivation. Three ⁶⁷Zn-labelled fertilisers, ZnO, zinc sulphate (ZnSO₄), and ZnO co-granulated with elemental sulphur (ZnOS⁰), were soil applied, and their contributions to the uptake of Zn by three consecutive crops, wheat, ryegrass, and corn, were assessed in a 294-d pot experiment. The contributions of Zn fertilisers followed the order:ZnSO₄ > ZnO=ZnOS⁰. The relative contributions of Zn fertilisers were lower in the first crop than in the subsequent crops. The overall recovery of applied Zn by the three crops was higher for ZnSO₄ than for ZnO and ZnOS⁰, reaching 1.56%, 0.45%, and 0.33% of the applied Zn, respectively. Zinc recovery by plants was very low, regardless of the source of Zn. Adding elemental sulphur to ZnO did not increase its effectiveness up to 294 d after application. Fertiliser contribution was higher for the subsequent crops than for the initial crop, indicating the importance of assessing the residual effects of Zn fertilisers.     

Crop species differ in root plasticity response to localised P supply

The effect of localised phosphorus (P) fertiliser placement and in particular, deep P fertiliser placement, on the comparative root growth and P uptake of fibrous vs tap‐rooted crops is not known. In this study, we examined the root growth and P uptake of wheat (Triticum aestivum L.), canola (Brassica napus L.), and narrow‐leaf lupin (Lupinus angustifolius L.) in a split‐root system and in columns with deep (19 cm) or shallow (5 cm) P fertiliser sources in glasshouse conditions. In the split‐root system, plants of all three species grown under heterogeneous soil P conditions absorbed more P and produced greater root and shoot biomass than those under homogeneous P supply. Root plasticity differed between species under heterogeneous soil P supply: canola and wheat allocated relatively more root biomass and root length to the high P zone than narrow‐leaf lupin. In the column experiment, there was no difference in the amount of P accumulated in shoots of any crops grown in the deep vs shallow P fertiliser treatments. Root proliferation occurred within the shallow and deep‐P fertiliser bands in all three species; however, root distribution above or below the bands did not differ between deep or shallow P fertiliser treatments in any species. Whilst root plasticity responses to heterogeneous soil P supply differed among species, root architecture (fibrous vs taproot) did not confer any advantage or disadvantage to the acquisition of P from deep vs shallow P fertiliser bands. Moreover, whilst roots proliferate in the vicinity of P fertiliser bands, root distribution outside of the bands appears to remain unaltered in both fibrous and tap‐rooted crops during early growth.     

生物炭及生物炭-矿物复合物对菌根侵染、小麦和高粱营养的影响

The high price of synthetic fertilisers and the price barrier for biochar as a soil amendment have encouraged the exploration of using biochar in fertiliser replacement formulations. Biochars coupled with fertilisers can be applied at lower application rates to achieve benefits in plant growth and nutrition, as well as soil biological fertility.~It is necessary to evaluate the use of biochar as a fertiliser substitute.~Therefore, this study investigated the comparative influences of biochars, including {\it Acacia saligna} (AS), Simcoa jarrah (SJ) and Wundowie jarrah (WJ), mineral fertiliser with microbes (MF + M), biochar-mineral complex (BMC) and their combination on mycorrhizal colonisation, growth and nutrition of wheat in a glasshouse experiment and sorghum in field conditions. BMC + MF + M treatment produced higher mycorrhizal colonisation than MF + M alone, indicating that BMC had a significant role in increasing mycorrhizal colonisation.~SJ (treated with acetic acid) and MF + M treatments, as well as AS + MF + M application, showed si\-milar effects on mycorrhizal colonisation, but lower colonisation than the BMC~+~MF~+~M treatment.~Overall, the BMC + MF + M treatment supported the maximum shoot, root and total plant dry weight followed by AS + MF + M and WJ + MF + M. The~MF + M treatment had the maximum shoot N and K concentrations, while BMC + MF + M application had the maximum shoot P concentration. AS + MF + M and WJ + MF + M treatments supported the maximum N uptake by wheat shoots, while BMC + MF + M supported the maximum P uptake.~The results showed that biochars and BMCs could increase mycorrhizal colonisation, plant growth and nutrient uptake of wheat, particularly N, P, K, S and Zn. The field experiment confirmed that BMC application at a rate of 300 kg ha$^{-1}$ could increase the yield of irrigated sorghum on a loam soil and provide better applied P use efficiency compared to a water-soluble fertiliser alone. These results indicated that biochar-based fertilisers might increase the resilience and sustainability of dryland cropping in environments such as in Western Australia and warrant further field evaluation.     

Why short‐term biochar application has no yield benefits: evidence from three field‐grown crops

This study determines the impact of biochar, as a supplement, on soil nutrient availability and yields for three crops within commercial management systems in a temperate environment. Central to the suggestion of biochar benefits is an increase in soil nutrient availability, and here, we test this idea by examining crop nutrient uptake, growth and yields of field‐grown spring barley, strawberry and potato. Biochar produced from Castanea sativa wood was incorporated into a sandy loam soil at 0, 20 and 50 t/ha as a supplement to standard crop management practice. Fertilizer was applied normally for each of the three crops. The biochar contained substantial concentrations of Ca, Mg, K, P, but only K occurred at high concentration in water‐soluble analysis. The large concentration of extractable K resulted in a significant increase of extractable K in soil. The increased availability of K in biochar‐treated soil, with the exception of spring barley grain and the leaves of strawberry during the second year, did not induce greater tissue concentrations. In general, biochar application rate had little influence on the tissue concentration of any nutrient, irrespective of crop or sampling date. There was, however, evidence of a biochar‐induced increase in tissue Mo and a decrease in Mn, in strawberry, which could be linked to soil alkalinization as could the reduction in extractable soil P. These experiments show a single rotational application of biochar to soil had no effect on the growth or harvest yield of any of these field‐grown crops. Heavy metal analysis revealed small concentrations in the biochar (i.e. <10 μg/g biochar), with the largest levels for Ni, V and Cu.     

Yield and nitrogen use efficiency of wheat increased with root length and biomass due to nitrogen,phosphorus, and potassium interactions

Balanced applications of nitrogen (N), phosphorus (P), and potassium (K) are known to increase grain yield of wheat but the impact of the interactions among N, P, and K on root growth and nitrogen use efficiency (NUE) have not been proven. The aim of this study was to investigate the effect of balanced applications of N, P, and K on the rooting patterns and NUE of wheat. Two glasshouse experiments were conducted. A rhizobox study was used to assess the impact of interactions among N, P, and K fertilisers on total root length, biomass, specific root length, root length density, N use efficiency (NUE), and N uptake efficiency of the shoots (NUpE_shoot) and N nutrition index. In a separate pot study, plants were grown to maturity to confirm the effect of the observed changes in root growth on NUE, NUpE_grain, and grain/biomass yield. In the rhizobox experiment when plants were supplied with N+P+K, total root biomass increased approximately six‐fold relative to plants grown with N alone or with no fertiliser. Plants exposed to N+P+K had NUpE_shoot and NUE values that were five and ten times higher, respectively, than plants that received just fertiliser N. Plants supplied with N+P or N+P+K had N nutrition indices close to one (N‐adequate), while plants that only received N had an index of 0.62 (N‐deficient). The pot study confirmed that the changes in root length and biomass in plants exposed to N+P+K resulted in significant increases in NUE, NUpE_grain, shoot biomass, and grain yield at maturity. Interactions among fertiliser N, P, and K played a critical role in influencing root biomass and length, which was associated with increases in NUE, NUpE_shoot and NUpE_grain.     

THE 40K and 214BI (FROM 238U) CONTENTS OF ROTHAMSTED SOILS DETERMINED BY GAMMA SPECTROMETRY

The gamma spectra of 17 surface soils from the Rothamsted Classical Experiments, selected for contrasting potassium and phosphate fertiliser treatments, were obtained to measure their contents of K and ²¹⁴Bi (from ²³⁸U accumulated from phosphate fertilisers) contents, using the ⁴⁰K and ²¹⁴Bi photopeaks. The fate of the fertiliser residues are discussed for each Experiment, related to differences in fertiliser treatment and period of application. In 1978, potassium fertilisers increased soil K content by about 20% in Hoosfield (since 1852) and Barnfield (since 1843), and by about 7% in Broadbalk (since 1843). The K contents of the P and PNaMg plots in Barnfield suggest that Na substituted significantly for K in crop uptake. In Hoosfield and Barnfield (except the PK and PNaMg plots) phosphate fertilisers increased ^2l4Bi contents, but did not affect it in Broadbalk. A new method for the quantitative determination of the content of any radionuclide emitting gamma radiation, and whose photopeak can be clearly resolved in the gamma spectrum of the soil, is described. This involves measurements on the soil and on the calibration samples containing radionuclides other than those to be assayed, using the same ‘sample:detector’ geometry, and the establishment of a calibration curve with reference sources in an energy range suitable for interpolating the results for the energy of the radionuclide. The values thus obtained are shown to compare very favourably with a direct method in which standards containing various amounts of the test radionuclide are used to calibrate the equipment. By using 1 kg samples of < 2 mm soil non-destructively, both methods avoid sampling errors and the need for finely ground (< 0.15 mm) soil inherent in conventional chemical analysis.     

Nitrogen uptake and utilisation by bell pepper in subtropical australia 1 ∗

Concern over the pollution potential of nitrogen (N) fertilisers has prompted studies of the utilisation efficiency of applied N by crops. This study was conducted to determine the efficiency of N usage by bell pepper (Capsicum annuum L.) grown with plastic mulch and trickle irrigation, and to define a rate of applied N which is equal to uptake by the crop. The relationships between applied N (0, 70, 140, 210, and 280 kg/ha), nutrient uptake, and yield for spring and autumn bell pepper crops grown on a major soil type (Tropeptic Eutrustox) in the Bundaberg region of subtropical Australia were investigated. Maximum dry weight yield of fruit, leaves, roots, and stems corresponded with N210 to N280 for both spring and autumn crops. In addition, maximum fresh weight of marketable fruit corresponded with N210 to N280 for both seasons. Nitrogen uptake was equal to the applied rate at N140. Plant uptake of elements increased with applied N and, at N280, were ranked as follows: K> N> Ca> Mg > S > P. Fruit accumulated the greatest proportion of K, N, and P (40 to 64%, 40 to 64%, 49 to 76%, respectively), and only a comparatively small amount of Ca (6 to 7%). The efficiency of fruit production from absorbed applied N declined with increasing N rate. District standard rates of P, N, K, and S application exceeded uptake by plants grown at an equivalent N rate (differences of 68 and 65 kg P, 57 and 52 kg N, 32 and 24 kg K, and 19 and 24 kg S for spring and autumn, respectively). Because of the importance of pepper yield as a determinant in economic outcome and the relatively low cost of fertiliser N, application rates in excess of N140 are likely to continue by district growers in an attempt to maximise yield.     

Adaptive Phenotypic Differences to Low Potassium Soil of Two Cotton Genotypes with Various Potassium-Use Efficiencies

Cotton (Gossypium hirsutum L.) is one of the most important cash crops in the world, and potassium (K) is an important limiting factor for cotton farming. Therefore, it is critical to improve K-use efficiency by selecting or breeding cotton genotypes with high K-use efficiency. Through a pot experiment with low-K soil, this article documentes the differences in vessel element anatomy and root hair traits between two cotton genotypes with different K-use efficiencies at both seedling and boll stages. Experimental results showed that at the seedling stage both frequency and length of root hair in the genotype with high K-use efficiency were significantly greater than those of the genotype with low K-use efficiency, but the frequency and diameter of vessels were not significantly different between the two genotypes. In the boll stage, the vessel frequencies in root, stem, petiole, and carpophore; root hair frequency, and length of high K-use-efficiency genotype were all significantly greater than those of the low K-use-efficiency genotype. The denser and longer root hairs were often found and accompanied by thicker vessel elements in the genotype with high K-use efficiency. This means the genotype had greater nutrient uptake and transportation capacity. The root hairs, vessel elements in root, stem, petiole, and carpophore, formed a complete system for nutrient uptake and translocation. The results from this study provide valuable information for the breeding of high K-use-efficiency cotton.     

Root traits of different crops under rainfed conditions in the High Barind Tract of Bangladesh

Root traits of six different crops grown on residual soil moisture in the post–rainy season in the High Barind Tract (HBT) of Bangladesh were investigated to better understand their adaptation to this moisture‐limited environment. Deep‐rooting chickpea is the currently favored rainfed crop grown after rainy‐season rice in the HBT, but it is necessary to identify alternative crops to chickpea in order to avoid buildup of pests and diseases. Averaged over 2 y, barley (1.72 Mg ha^–1) produced significantly more grain than chickpea (1.4 Mg ha^–1) which, in turn, yielded better than linseed (1.0 Mg ha^–1), wheat (0.93 Mg ha^–1), and mustard (0.77 Mg ha^–1). Lentil did not produce any grain at all. Grain yield for all crops increased as total root length increased above a threshold value of 0.05 to 0.1 km m^–2. In general, grain yield increased as the proportion of total root produced below 60 cm depth increased, although barley also had thin roots that could more effectively extract soil moisture. Expression of root traits varied considerably between seasons, which was attributable to the different rainfall patterns and bulk‐density characteristics of the soil profile in the 2 years of the study. Although favorable root traits, particularly rooting ability below 60 cm, are a prerequisite for acceptable yield levels of crops grown on residual soil moisture in the HBT, it is recognized that farmers' choice of a post‐rice crop will depend on its economic return or food‐security value.     

开发更高效的生物炭肥料提高辣椒产量和质量

Utilization of biochar at high application rates can increase soil C and crop yields, decrease greenhouse gas emissions and reduce nutrient run-off from soils. However, the high application rate of 10 t ha-1may not return a profit to the farmer due to the high cost of biochar. In this study biochar was modified through pre-treating the biomass and post-treating with phosphoric acid, minerals and different chemical fertilisers to study the effects of two new enhanced biochar fertilisers on the yield and quality of green pepper in a field experiment with 5 fertilisation treatments and 3 replications. The two new biochar fertilisers significantly(P 0.05) increased the yield of green pepper(11.33–11.47 t ha-1), compared with the conventional chemical fertiliser(9.72 t ha-1). The biochar fertiliser treatments improved the vitamin C content of green pepper from 236.99 to 278.28 mg kg-1, and also significantly(P 0.05) reduced the nitrate content from 132.32 to 101.92 mg kg-1, compared with chemical fertiliser. This study indicated that, compared to the use of conventional chemical fertiliser, all of the biochar fertiliser treatments could significantly improve the yield and quality of green pepper.     

The Effects of Long‐term Fertiliser Applications on Soil Organic Carbon and Hydraulic Properties of a Loess Soil in China

Based on a 28‐year in situ experiment, this paper investigated the impacts of organic and inorganic fertiliser applications on soil organic carbon (SOC) content and soil hydraulic properties of the silt loam (Eumorthic Anthrosols) soils derived from loess soil in the Guanzhong Plain of China. There were two crop (winter wheat and summer maize) rotations with conventional tillage. The treatments included control without fertiliser application, organic manure application (M), chemical fertiliser application (NP), and the application of organic manure with chemical fertiliser (MNP). The results showed that the 28‐year organic manure applications (M and MNP) significantly (p < 0·05) increased SOC content at surface layer (0–10 cm), but the effect of chemical fertilisers alone on SOC was not significant. Organic manure treatments (M and MNP) apparently improved soil hydraulic properties. Compared with control, field capacity and total porosity significantly (p < 0·05) increased while soil bulk density significantly (p < 0·05) decreased for organic manure applications. The M and MNP treatments increased soil water retentions by 3·2–10·8%, which was dependent of suction tensions. However, the NP treatment had no significantly impact on soil water retention compared with control. Neither organic nor inorganic fertiliser applications significantly changed saturated hydraulic conductivity. However, a clear difference was observed for unsaturated hydraulic conductivity between the M and the control at 0–5 cm. Overall, long‐term applications of organic manuring increased SOC content and amended soil hydraulic properties. However, the effects of chemical fertilisers on these soil properties were limited. Copyright © 2015 John Wiley & Sons, Ltd.     

Alterations in yield,physicochemical components and mineral composition of onion following organic manure and inorganic nitrogen application

Onion is the one of the most important vegetable crops grown extensively throughout the world; hence, understanding the response of the crop to the form and amount of N provided is of immense importance. In a field experiment, poultry and cattle manure (at 10?t/ha) were compared with four inorganic nitrogen (N) application levels (0, 60, 90 and 120?kg?N/ha), and six combinations of manure and N applications were investigated. Plant growth and total yield (kg/ha) significantly increased, when N application increased from 0 to 120?kg/ha, with or without added poultry manure. Plant height, leaf number and neck thickness were significantly reduced at 0?kg/ha?N plus cattle manure. The bulb ascorbic acid concentration significantly increased with the use of poultry manure (15.94?mg/100?g) and cattle manure (15.94?mg/100?g), compared with 120?kg/ha inorganic N (11.42?mg/100?g). No significant effects were observed on total phenolics and total soluble solids of onion bulbs following the different fertiliser treatments. Cattle manure increased P and K concentrations, whilst poultry manure significantly increased Zn and Fe concentrations in onion bulbs. Onion bulb Ca and Mg concentrations were lower when cattle manure (0.19% and 0.12%) was used than when other organic or inorganic fertilisers were used. Therefore, organic manure increases the concentrations of certain minerals in onions, compared with inorganic N application, without negatively affecting bulb size.     

Phosphorus‐use efficiency by corn genotypes

Phosphorus (P) deficiency is a principal yield‐limiting factor for annual crop production in acid soils of temperate as well as tropical regions. The objective of this study was to screen nine corn (Zea mays L.) genotypes at low (0 mg P kg^‐1), medium (75 mg P kg^‐1), and high (150 mg P kg^‐1) levels of P applied in an Oxisol. Plant height, root length, shoot dry weight, root dry weight, shoot‐root ratio, P concentration in shoot and root, P uptake in root and shoot, and P‐use efficiency parameters were significantly (P<0.01) influenced by P treatments. Significant genotype differences were found in plant height, shoot and root dry weight, P uptake in root and shoot, and P‐use efficiency. Based on dry matter production and P‐use efficiency, genotypes were classified as efficient and responsive, efficient and nonresponsive, nonefficient and responsive, and nonefficient and nonresponsive.     

菜地土壤有机碳分级以及总量变化的动态特征研究

Fertilisers significantly affect crop production and crop biomass inputs to soil organic carbon（SOC）. However, the long-term effects of fertilisers on C associated with aggregates are not yet fully understood. Based on soil aggregate and SOC fractionation analysis, this study investigated the long-term effects of organic manure and inorganic fertilisers on the accumulation and change in SOC and its fractions, including the C concentrations of free light fraction, intra-aggregate particulate organic matter（POM） and intra-aggregate mineral-associated organic matter（MOM）. Long-term manure applications improved SOC and increased the concentrations of some C fractions. Manure also accelerated the decomposition of coarse POM（cPOM） into fine POM（fPOM） and facilitated the transformation of fPOM encrustation into intra-microaggregate POM within macroaggregates. However, the application of inorganic fertilisers was detrimental to the formation of fPOM and to the subsequent encrustation of fPOM with clay particles, thus inhibiting the formation of stable microaggregates within macroaggregates. No significant differences were observed among the inorganic fertiliser treatments in terms of C concentrations of MOM, intra-microaggregate MOM within macroaggregate（imMMOM） and intra-microaggregate MOM（imMOM）. However, the long-term application of manure resulted in large increases in C concentrations of MOM（36.35%）, imMMOM（456.31%） and imMOM（19.33%） compared with control treatment.     

The response of properties of soil cropped with shell beans and treated with disinfectant and fertiliser during the plant growing season

Disinfectants and fertilisers exert strong impact on soil processes by affecting the structure and the activity of the soil microbial community. Most relevant studies examined these impacts independently, under laboratory conditions and without crop cover. In this study, we have monitored the response of soil chemical, microbial, and biochemical properties to disinfectant and fertiliser treatments in field plots cultivated with beans. The measured properties comprised microbial C and N, asparaginase, gultaminase, urease, and acid phosphomonoesterase activities and contents of organic N, organic C, inorganic N, and inorganic P. We ran four different treatments using different combinations of chemical (metham sodium) and biological disinfectant (a mixture of neem cake and essential oils) and fertilisers (NPK 8-16-24 and cow manure) in plots cultivated with shell beans, while the control soil was neither treated nor cropped with beans. The data were expressed as percentage (%RC) in relation to the control values. The disinfectant and fertiliser treatments had less impact on soil properties compared to bean crop growth (except for microbial C and N, and content of organic C). In comparison to the control, higher activities of urease and asparaginase and content of inorganic N were recorded in bean cropped plots at the stage of seedlings (June), while higher activities of acid phosphomonoesterase and glutaminase and content of organic N were recorded at the stage of plant flowering (August). In October, the values of all properties were higher in the control plots compared to the treated plots. The joint effect of disinfectants x fertilisers affected the response of content of organic C and N and extractable P and glutaminase activity. The %RC of the properties exhibited more negative values in plots treated with chemical disinfectant and chemical fertiliser than in the other treatments. We suggested that the response of soil properties to disinfectants and fertilisers were influenced by the growth of P. vulgaris.     

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P‐efficient genotypes. Two efficient and two inefficient genotypes were investigated for P‐efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P‐uptake rate of roots but decreased root‐to‐shoot ratio, root‐hair length, and P‐utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot–dry matter yield and relative shoot‐growth rate at low P supply, and therefore can be considered as P‐efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P‐utilization efficiency and that of CIP 384321.3 to both higher P‐uptake efficiency in terms of root‐to‐shoot ratio and intermediate P‐utilization efficiency. Phosphorus‐efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P‐utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P‐utilization efficiency. Simulation of P uptake revealed that no other P‐mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described.     

Release of carbon and nitrogen from fodder radish (Raphanus sativus) shoots and roots incubated in soils with different management history

Plant roots are generally considered to decompose slower than shoots and contribute more to accumulation of soil organic matter, and management history is expected to shape the structure and function of decomposer communities in soil. Here we study the effect of chemical characteristics of shoots and roots from fodder radish (Raphanus sativus oleiformis L.), a widely used cover crop, on the release of their C and N after addition to soil. Shoots and roots were incubated for 180?d at 20°C using four soils with different management histories (organic versus mineral fertiliser, with and without use of cover crops), and the release of CO₂ and extractable mineral N was determined. More shoot C than root C was mineralised during the first 10?d of incubation. After 180?d, 58% of the C input was mineralised with no difference between shoots and roots. At the end of incubation, shoots had released more N (42% of shoot N) than roots (28% of root N). Moreover, management history did not affect net mineralisation of added plant C. Residues incubated in soil with a management history involving cover crops showed an enhanced net N mineralisation. Therefore, long-term decomposition of C added in radish shoots and roots is unaffected by differences in chemical characteristics or soil management history. However, the net mineralisation of N in shoots is faster than for N in roots, and net N mineralisation of added materials is higher in soil with than without a history of cover crops.

Abbreviations: CC: cover crop; IF: inorganic fertilizer; M: manure     

Upland rice genotypes evaluation for phosphorus use efficiency

Phosphorus (P) deficiency is one of the most important yield‐limiting factors in acid soils in various parts of the world. The objective of this study was to evaluate the growth and P‐use efficiency of 20 upland rice (Oryza sativa L.) genotypes at low (0 mg P kg^‐1), medium (75 mg P kg^‐1), and high (150 mg P kg^‐1) levels of applied P on an Oxisol. Plant height, tillers, shoot and root dry weight, shoot‐root ratio, P concentration in root and shoot, P uptake in root and shoot, and P‐use efficiency were significantly (P<0.01) affected by level of soil P as well as genotype. Shoot weight and P uptake in shoot were found to be the plant parameters most sensitive to P deficiency, suggesting that these two parameters may be most suitable for screening rice genotypes for P‐use efficiency under greenhouse conditions.     

Potassium fractions with other nutrients in crops: A review focusing on the tropics

Potassium (K), a plant nutrient with diverse roles to play in plant metabolism, is required in large amounts by most crops. It interacts with many other plant constituents to affect crop yield and quality. The magnitude of this interaction is high in areas of high cropping intensity, as in the tropics. The interaction of nutrients with K may be in the soil or in plant. Potassium modifies ammonium (NH₄ ⁺) ion fixation in soils to restrict nitrogen (N) availability. On the other hand, an antagonistic effect between K and NH₄ absorption has been suggested in which K absorption is restricted. Similarly, magnesium (Mg) or calcium (Ca) deficiency occurs from ion antagonism in acid soils following K fertilization and in soils with high exchangeable K. Sulfur (S) has been reported to increase K absorption and productivity of oilseed crops. With increasing levels of applied or soil K, the severity of phosphorus (P)‐induced zinc (Zn) deficiency in corn has been observed to decrease. Application of K decreases manganese (Mn) content and iron (Fe) toxicity in rice. Application of K has been reported to decrease B levels in plants and to increase incidence of boron (B) deficiency. Top‐dressing with K fertilizer was reported to lower the copper (Cu) content of alfalfa forage. In root, sugar‐producing, or fiber‐producing crops, the sodium (Na) and K relationship is important with the specific response to either element depending on which element is in low or high supply. Molybdenum (Mo) stimulated K uptake in alfalfa and com. In intensive agriculture with high‐yielding single crops or with multiple crops per year, farm management must include strategies to maintain substantial K reserves in the soil and to balance K nutrition with other fertilization practices.