Agronomic evaluation of controlled release of micro urea encapsulated in rosin maleic anhydride adduct

Abstract

Plant derived bio-based materials are environmental-friendly and provide a cheap and an attractive source for synthesis of controlled release urea fertilizers which have positive impact on plants’ health. In this work, application of rosin-maleic anhydride adduct encapsulated controlled release micro urea fertilizer (RA-mCRUF) was investigated for the optimization of its controlled urea release properties and evaluation of growth promoting effect on maize (Zea mays) plant under three different soil texture classes. Through response surface methodology, the independent response variables, were optimized for controlled release response of urea. Study found optimized coating repeats, 5.00 cycles; drying time, 11.71?h; and particle size, 41.82?µm; at urea release response of 331.62?mg L^?1 in distilled water. Optical microscopy images further demonstrated a more compact and homogeneous surface of RA-mCRUF without any coating defects. Besides, RA-mCRUF predicted a better growth performance of maize plant in clay loam soil. Moreover, RA-mCRUF treated maize plant showed 9.0–24.5?mg g^?1 increase in chlorophyll contents and 7.44–12.75?g rise in plant dry biomass. This work successfully produced a new type of RA-mCRUF which has applied role in soil nutrients conservation and addressing effectively food security through crops protection.     

Urea release from Osmocote® fertilizers in water and simulated wetland rice soil

Abstract

Average urea release (UR) from two Osmocote fertilizers (40–0–0 and 41–0–0) in water at 38°C and in a simulated wetland system using Crowley soil under greenhouse conditions has been studied. UR from the Osmocote granules in water seemed to be a diffusion process controlled by urea concentration gradients. It was faster when the swelling of granules was restricted than when swelling of granules was not restricted. The UR‐time curves for both Osmocote fertilizers placed at different depths (0–1, 5–10, and 10–15 cm) in simulated wetland soil were different from those placed in water. UR in the soil was rather slow; therefore, these fertilizers may not be suitable for short‐ to medium‐duration wetland rice varieties.     

Bioavailability of Inorganic Phosphorus Fractions in Calcareous Soils Estimated by Neubauer Technique,Iron‐Impregnated Filter Paper,and Chemical Tests

Abstract

Plants commonly suffer from phosphorus (P) deficiency in calcareous soils. Plant responses to P application on such soils mostly show poor correlation with their soil test P values. Experiments were conducted on 24 different soil samples under laboratory and greenhouse conditions to illustrate the relationship of various inorganic P fractions in different calcareous soils with P uptake by plants, P extraction by iron‐impregnated filter paper, and P soil test values estimated by 0.5M NaHCO₃ and ammonium bicarbonate diethylene triamine penta‐acetic acid. Total P in the 24 soils ranged from 652 to 1245 mgkg^?1 with a mean of 922 mgkg^?1. A major proportion (98%) of inorganic P was in HCl‐P (Ca‐bound) form. The HCl‐P (Ca‐bound) ranged from 296 to 729 with a mean of 480 mgkg^?1. The iron (Fe) and aluminum (Al)‐P (NaOH‐P) ranged from 0.92 to 12 mgkg^?1 with a mean of 1.57 mgkg^?1. The Fe‐P (citrate‐dithionite bicarbonate) ranged from 0.22 to 4.40 mgkg^?1 with a mean of 5.99 mgkg^?1. Data regarding P release from the soil matrix obtained by desorption with iron‐impregnated filter paper was best described by the Elovich equation. Range of slope and intercept values were found to be 5.48 to 17.3 and 17.23 to 56.27 mgkg^?1, respectively. Intercept values calculated for the Elovich equation may be related to labile P initially available for plant uptake in soils. Intercept values calculated for the Elovich equation correlated (r=0.77) significantly (p<0.01) with NaHCO₃ extractable (Olsen‐P)P. Significant correlation (p<0.05) of intercept with CDB‐P (r=0.44) and of slope with HCl‐P (0.43) suggested that the initially available P, regulated through CDB‐P, is replenished by HCl‐P [calcium (Ca) bound].     

Controlled‐release urea decreased ammonia volatilization and increased nitrogen use efficiency of cotton

Excessive nitrogen (N) fertilizer input leads to higher N loss via ammonia (NH₃) volatilization. Controlled‐release urea (CRU) was expected to reduce emission losses of N. An incubation and a plant growth experiment with Gossypium hirsutum L. were conducted with urea and CRU (a fertilizer mixture of polymer‐coating sulfur‐coated urea and polymer‐coated urea with N ratios of 5 : 5) under six levels of N fertilization rates, which were 0% (0 mg N kg⁻¹ soil), 50% (110 mg N kg⁻¹ soil), 75% (165 mg N kg⁻¹ soil), 100% (220 mg N kg⁻¹ soil), 125% (275 mg N kg⁻¹ soil), and 150% (330 mg N kg⁻¹ soil) of the recommended N fertilizer rate. For each type of N fertilizer, the NH₃ volatilization, cotton yield, and N uptake increased with the rate of N application, while N use efficiency reached a threshold and decreased when N application rates of urea and CRU exceeded 238.7 and 209.3 mg N kg⁻¹ soil, respectively. Ammonia volatilization was reduced by 65–105% with CRU in comparison to urea treatments. The N release characteristic of CRU corresponded well to the N requirements of cotton growth. Soil inorganic N contents, leaf SPAD values, and net photosynthetic rates were increased by CRU application, particularly from the full bloom stage to the initial boll‐opening stage. As a result, CRU treatments achieved significantly higher lint yield by 7–30%, and the N use efficiency of CRU treatments was increased by 25–124% relative to that of urea treatments. These results suggest that the application of CRU could be widely used for cotton production with higher N use efficiency and lower NH₃ volatilization.     

Determination of DTNB-reactive sulphhydryl groups in soil humic acids: their enrichment in humic acids from volcanic acid soils

Thirteen acid soils were collected from typical volcanic regions in Japan (S content: 0.9–4.1, mean = 2.2g kg^?1; pH (H₂O): 2.81–3.93, mean = 3.33), as well as nine reference soils (S: 0.6–1.7, mean= 1.1 gkg^?1; pH(H₂O): 4.10–4.74, mean = 4.47). Humic acids were extracted from the soils separately with 0.1 M NaOH and precipitated by acidification (pH = 2, HCl). After purification, the humic acids were subjected to colorimetric analysis using a DTNB reagent [5,5′-dithiobis(2–nitrobenzoic acid] for the active -SH group. Since humic acids have significant absorption at 4I2 nm, the coloured compound (5–mercapto-2–nitrobenzoic acid) was separated from the humic acids by ultrafiltration or solvent extraction prior to the colorimetric measurement. Humic acids also caused discoloration of the coloured compound when they coexisted in the reaction solutions. Thus, the reproducible determination of -SH was accomplished by employing a standard addition technique (-SH standard: cysteine). Although -SH contents obtained by the ultrafiltration method were considerably higher than those by the solvent-extraction method, probably due to the denaturation of humic acids by the higher buffer concentration used in the ultrafiltration method, they correlated well with each other. The humic acids from acid soils contained apparently higher concentrations of -SH (120–510, mean = 270mg S kg^?1 by the ultrafiltration method; 8–110, mean = 38mg S kg^?1 by the solvent-extraction method) compared to those from reference soils [20–260, mean = 90mg S kg^?1 by the former; not detectable (<5)-34, mean = 11 mg S kg^?1 by the latter]. This -SH enrichment in the humic acids from acid soils may result from the degradation and subsequent humification of S-rich debris of plants and micro-organisms and/or direct incorporation of volcanic acid gas (H₂S) into the humic acids.     

Short‐term effects of application of different rates of inorganic P and residue P on soil P pools and wheat growth

Phosphorus (P) can be added to soil as inorganic P or crop‐residue P, but little is known about how these two forms of P addition affect soil P pools and how their effect changes with the rate of P addition. A glasshouse experiment was conducted to assess the effect of inorganic P and P added as residues at different rates on (1) soil P pools at two time points: immediately after amendment and 42 d later, and (2) growth and P uptake by wheat at flowering (day 42). Three types of legume residues (faba bean young shoot, chickpea mature shoots with pods, and white lupin mature shoots without pods) were added to a loamy‐sand soil at a rate of 5 or 15 g residue kg^–1. Inorganic P was added at four different rates (3, 10, 30, and 100 mg P kg^–1) to give P‐addition rates corresponding to the total P added with the different residues at the two residue rates. Soil P pool concentrations (microbial P, resin‐P, NaHCO₃‐P, NaOH‐P, HCl‐P, and residual P) and wheat growth and P uptake (shoot and root) were measured after 6 weeks. Compared to inorganic P addition, P added with residues led to a 10%–80% greater increase in shoot biomass at the two highest P‐addition rates. Wheat P uptake was positively correlated with resin‐P and microbial‐P concentrations in residue‐P‐amended soil, but with resin‐P and NaOH‐P_i concentrations in soil amended with inorganic P. The concentration of HCl‐P decreased by up to 30% from day 0 to day 42 in the residue treatments and that of residual P decreased by about 20% in all treatments during this period suggesting that these nonlabile P pools are quite dynamic and could serve as P source for plants.     

控释氮肥对大白菜产量和品质的影响及其机理研究

田间试验研究了控释氮肥不同品种及不同用量对大白菜产量和品质的影响,并从养分释放、包膜特性等方面探讨其作用机理。结果表明,控释氮肥能显著提高大白菜产量和品质。与同期追施等氮量尿素相比,施用控释氮肥可使大白菜产量提高8.2%～16.8%;莲座末期功能叶和收获期球叶NO-3-N含量分别降低14.3%～39.9%和12.1%～21.4%,收获期球叶Vc含量平均提高24.8%。控释氮肥用量减半后,大白菜产量及叶片NO3--N与Vc含量都未受到显著影响。研究证实,由于控释氮肥中的氮素是缓慢地释放出来,在大白菜生育前期施用,仍能较充分满足生育中后期株体对氮素的需求,控释期不同的两个氮肥品种混合施用较单一施用的效果更好。不同控释氮肥品种氮素释放特征的差异与肥料包膜的厚度、膜断面及表面孔隙状况不同有关。     

Nitrogen fertilizer–induced mineralization of soil organic C and N in six contrasting soils of Bangladesh

A 90‐day laboratory incubation study was carried out using six contrasting subtropical soils (calcareous, peat, saline, noncalcareous, terrace, and acid sulfate) from Bangladesh. A control treatment without nitrogen (N) application was compared with treatments where urea, ammonium sulfate (AS), and ammonium nitrate (AN) were applied at a rate of 100 mg N (kg soil)^–1. To study the effect of N fertilizers on soil carbon (C) turnover, the CO₂‐C flux was determined at nine sampling dates during the incubation, and the total loss of soil carbon (TC) was calculated. Nitrogen turnover was characterized by measuring net nitrogen mineralization (NNM) and net nitrification (NN). Simple and stepwise multiple regressions were calculated between CO₂‐C flux, TC, NNM, and NN on the one hand and selected soil properties (organic C, total N, C : N ratio, CEC, pH, clay and sand content) on the other hand. In general, CO₂‐C fluxes were clearly higher during the first 2 weeks of the incubation compared to the later phases. Soils with high pH and/or indigenous C displayed the highest CO₂‐C flux. However, soils having low C levels (i.e., calcareous and terrace soils) displayed a large relative TC loss (up to 22.3%) and the added N–induced TC loss from these soils reached a maximum of 10.6%. Loss of TC differed depending on the N treatments (urea > AS > AN >> control). Significantly higher NNM was found in the acidic soils (terrace and acid sulfate). On average, NNM after urea application was higher than for AS and AN (80.3 vs. 71.9 and 70.9 N (kg soil)^–1, respectively). However, specific interactions between N‐fertilizer form and soil type have to be taken into consideration. High pH soils displayed larger NN (75.9–98.1 mg N (kg soil)^–1) than low pH soils. Averaged over the six soils, NN after application of urea and AS (83.3 and 82.2 mg N (kg soil)^–1, respectively) was significantly higher than after application of AN (60.6 mg N (kg soil)^–1). Significant relationships were found between total CO₂ flux and certain soil properties (organic C, total N, CEC, clay and sand content). The most important soil property for NNM as well as NN was soil pH, showing a correlation coefficient of –0.33** and 0.45***, respectively. The results indicate that application of urea to acidic soils and AS to high‐pH soils could be an effective measure to improve the availability of added N for crop uptake.     

Soil organic phosphorus in tropical forests: an assessment of the NaOH–EDTA extraction procedure for quantitative analysis by solution 31P NMR spectroscopy

The extraction of soil organic phosphorus by the NaOH–EDTA procedure was assessed in detail for a tropical forest soil (clay‐loam, pH 4.3, total carbon 2.7%). Optimum conditions for the quantification of soil organic phosphorus and characterization of its composition by solution ³¹P NMR spectroscopy were extraction in a solution containing 0.25 m NaOH and 50 mm Na₂EDTA in a 1:20 solid to solution ratio for 4 hours at ambient laboratory temperature. Replicate analyses yielded a coefficient of variation of 3% for organic phosphorus as a proportion of the spectral area. There was no significant difference in total phosphorus extraction from fresh and air‐dried soil, although slightly more organic phosphorus and less paramagnetic ions were extracted from dried soil. The procedure was not improved by changing the concentration of NaOH or EDTA, extraction time, or solid to solution ratio. Pre‐extraction with HCl or Na₂EDTA did not increase subsequent organic phosphorus extraction in NaOH–EDTA or improve spectral resolution in solution ³¹P NMR spectroscopy. Post‐extraction treatment with Chelex resin did not improve spectral resolution, but removed small concentrations of phosphorus from the extracts. Increasing the pH of NaOH–EDTA extracts (up to 1.0 m NaOH) increased the concentration of phosphate monoesters, but decreased DNA to an undetectable level, indicating its hydrolysis in strong alkali. The standardized NaOH–EDTA extraction procedure is therefore recommended for the analysis of organic phosphorus in tropical forest soils.     

Influence of nitrogen and weed management on the productivity of upland rice

Nitrogen and weeds are two important factors that influence the productivity of rainfed upland rice (Oryza sativa L.) in tropical Asia. A low recovery of applied fertilizer N in rainfed uplands is generally associated with high nitrate leaching losses and weed interferences. Field experiments were conducted during the wet seasons of 2002 and 2003 at the research farm of Central Rainfed Upland Rice Research Station, Hazaribag, Jharkhand, India, to determine the response of upland rice to nitrogen applied at 60 kg N ha^–1 as different forms of urea (single pre‐plant application of controlled‐release urea, single pre‐plant application of urea supergranules, and split application of prilled urea with or without basal N) against no N application under three weed‐control regimes (unweeded, pre‐emergence application of butachlor at 1.5 kg a.i. ha^–1 supplemented with one single hand weeding or two hand weedings). The response of rice to applied N varied greatly among the three weed‐control regimes. Across the different N treatments, the application of 60 kg N ha^–1 resulted in a grain‐yield increase above the unfertilized control of only 0.24 Mg ha^–1 in unweeded treatments, whereas yields increased by 1.07 Mg ha^–1 when butachlor application was supplemented with a single hand weeding and by 1.28 Mg ha^–1 with two hand weedings. Among the weed‐control measures, hand weeding twice produced highest grain yield in both years. The comparison of different forms of urea showed that a single pre‐plant application of controlled‐release urea resulted in average grain yields of 1.57 and 1.87 Mg ha^–1 compared to 1.32 and 1.30 Mg ha^–1 in the case of the recommended practice of split‐applied prilled urea in the years 2002 and 2003, respectively. The highest agronomic N use efficiency of 15–20 kg grain per kg N applied and the highest apparent N recovery of 39%–45% were attained with controlled‐release urea, suggesting that this N form is particularly beneficial for upland‐rice cultivation under variable rainfall conditions, provided weeds are controlled.     

草酸/草酸盐对森林暗棕壤的磷释放效应

模拟森林凋落物淋洗液中的草酸/草酸盐浓度范围,设计了不同浓度草酸/草酸盐溶液一次性浸提和多次连续浸提系列实验,其中的草酸(阴离子)载荷量为0~200 mmol kg-1。结果表明,草酸能显著促进暗棕壤A1层(腐殖质层)磷的释放,土壤磷溶出量随草酸溶液浓度升高而线性增加;但对B层土壤磷的释放效应相对较弱,草酸浓度低于5mmol L-1时B层磷的释放不明显。pH 5.16草酸钠溶液比相同浓度的草酸溶液具有更高的解磷效率,在设置二者浓度为0.5~20.0 mmol L-1时,前者的解磷量是后者的1.51~2.98倍,推断草酸盐溶液或凋落物淋洗液中草酸(盐)类物质促进暗棕壤磷释放的主要机理在于草酸阴离子(C2O42-)配位反应。草酸盐对暗棕壤磷的释放效应具有一定累加性,土壤磷释放量主要由草酸阴离子累积载荷量决定,而与其加入方式(多次或一次性)关系不大;当以pH5.16草酸钠溶液加入时,土壤磷释放量Y(mgkg-1)与草酸阴离子累积载荷量X(mmol kg-1)间的回归方程为Y=-0.000 4X2 0.176 6X 0.425 3,R2=0.990 2。仅以凋落物层溶出的草酸(阴离子)量进行估计,由此增加的A1层土壤磷释放量达2.40 kg hm-2a-1,大约相当于中龄林年吸收磷量的1/3~1/5,因此其实际作用是不可忽视的。     

Urea retention and uptake by avocado and apple leaves

Solution retention by avocado (Persea americana cv. Fuerte) and apple (Mallus domestica Burkh. cv. Anna) leaves was measured by weight gain of detached leaves after dipping them in solutions of two surfactants and by analysis of various concentrations of urea retained at zero time on surfaces of attached leaves. Linear regression equations were calulated, relating leaf area and retention of solution. The slope of the equation represents the retention of solution on the leaf surface, and its intercept represents the value retained on the leaf margin. Solution retained on leaf surface was 2.5–2.6 and 5.4–6.4 mg/cm² for ‘old’ avocado and apple leaves, respectively. Retention on the serrated leaf margin of the apple was greater than on the smooth margin of the avocado. The abaxial leaf surfaces retained approximately 62% and 83% of the total solution retained by the avocado and the apple leaves, respectively.

The rate of urea uptake was proportional to the applied concentration and reached in avocado 65–85% within 2–5 days and over 90% in apple within 2 days. The rate of urea uptake by avocado was similar on ‘Young’ and ‘old’ leaves, similar from either Triton X‐100 or L‐77 surfactants, and similar through abaxial and adaxial surfaces. The nitrogen enrichment from foliar application of urea was related to retention and threshold of phytotoxicity rather than to rate of uptake. Older leaves of avocado showed some phytoxicity to 4% urea. Young leaves were damaged by repeated 2% application and flowers by 0.5–1.0%.

The actual nitrogen enrichment in avocado, which could be predicted accurately from measurement of urea retention, was 43% following three successive applications of 3% urea in 12 days.     

Evaluation of Phosphorus Pools and Fractions in an Acid Tropical Soil Recapitalized with Different Phosphorus Sources

Abstract

Bray 1 phosphorus (B1P) and sequential phosphorus (P) fractions were determined on soils treated with triple superphosphate (TSP), Gafsa (GPR), and Christmas Island phosphate rocks (CIPR), respectively, with and without manure. The fractions extracted in decreasing lability were iron oxide–impregnated paper strip P (Pi‐strip P), inorganic (Pi), and organic (Po) bicarbonate (NaHCO3‐Pi and ‐Po), hydroxide [sodium hydroxide (NaOH)‐Pi and ‐Po], hydrochloric acid (HCl) P, and residual (residue P). The magnitude of B1P was in the order TSP>GPR=CIPR. Average B1P from PRs was two‐fold the amount in TSP, whereas that of the fractions was NaOH‐P>Residue P<sodium bicarbonate (NaHCO₃) P<Pi‐strip P <HCl. Bray 1 extracted mainly the most labile fractions (Pi‐strip P and NaHCO3‐Pi), and plant P uptake was correlated mainly to NaOH‐Po and NaHCO₃‐Pi. Magnitude of various fractions differed between TSP and PRs. Both B1P and the fractions were equally correlated to P uptake (R²=0.38**). Nevertheless, sequential fractionation appears to be a powerful tool to identify the P status and availability in soil.     

Vegetative Growth,Yield and Leaf Mineral Composition in Strawberry (Fragaria × Ananassa DUCH. CV. Pajaro) as Influenced using Nickel Sulfate and Urea Sprays

In this study, interactions of nickel sulfate and urea sprays on vegetative growth, yield and leaf mineral contents in strawberry were investigated. Rooted Pajaro strawberry plants were potted in 3 liter pots filled with soil, leaf mold and sand (1:1:1, v/v/v). Established plants were foliar sprayed with nickel sulfate at 0, 150, 300 and 450 mg L^?1 and urea 0 and 2 g L^?1 concentrations. Results indicated that nickel (Ni; 300 mg L^?1) plus urea (2 g L^?1) significantly increased the yield and runner numbers. Nickel sulfate at the rate of 300 and 150 mg L^?1and urea (2 g L^?1) significantly increased the crown numbers. The greatest root fresh and dry weights were obtained from untreated plants. Urea at 2 g L^?1 without nickel significantly increased shoot fresh and dry weights. Nickel at 450 mg L^?1 without urea significantly increased Ni concentration in leaves. Overall, nickel sulfate at 150 and 300 mg L^?1 along with urea at 2 g L^?1 were the best treatments.     

Adsorption of Phosphate from Aqueous Solution Using an Iron–Zirconium Binary Oxide Sorbent

In this study, an iron?Czirconium binary oxide with a molar ratio of 4:1 was synthesized by a simple coprecipitation process for removal of phosphate from water. The effects of contact time, initial concentration of phosphate solution, temperature, pH of solution, and ionic strength on the efficiency of phosphate removal were investigated. The adsorption data fitted well to the Langmuir model with the maximum P adsorption capacity estimated of 24.9?mg P/g at pH?8.5 and 33.4?mg P/g at pH?5.5. The phosphate adsorption was pH dependent, decreasing with an increase in pH value. The presence of Cl^?, SO ₄ ^2? , and CO ₃ ^2? had little adverse effect on phosphate removal. A desorbability of approximately 53?% was observed with 0.5?M NaOH, indicating a relatively strong bonding between the adsorbed PO ₄ ^3? and the sorptive sites on the surface of the adsorbent. The phosphate uptake was mainly achieved through the replacement of surface hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface. Due to its relatively high adsorption capacity, high selectivity and low cost, this Fe?CZr binary oxide is a very promising candidate for the removal of phosphate ions from wastewater.     

Chemistry of Cr in some Swedish soils. 6. Native P transformation and changes in pH and cation exchange capacity in two soils incubated with potassium chromate

Abstract

Transformation of native P and changes in water pH and cation exchange capacity (CEC‐pH 7) were investigated in acid (I) and neutral (IV) soil incubated with 0, 50 and 100 mg Cr/kg for 3 months. Phosphorus was sequentially obtained as P‐resin, P‐NaHCO₃, P‐NaOH and P‐HCl, with the P‐NaHCO₃ and P‐NaOH being separated into organic and inorganic fractions. The low Cr level had little impact on the parameters. The high level increased the pH from 5.1 to 7.3 and from 6.8 to 7.5 in soils I and IV, respectively, while also significantly (P=5%) increasing CEC and decreasing P‐resin content. Subsequent to the Cr treatment, total P‐NaHCO₃ significantly declined in Soil I, but did not change markedly in Soil IV. Although total P‐NaOH was not affected by the Cr applications, its inorganic form doubled in Soil IV. Most of the total P‐NaHCO₃ and P‐NaOH was in organic form. Whereas P‐HCl was stable in Soil IV, the P nearly doubled in Soil I at the expense of P‐NaHCO₃ (r = ‐0.94**). pH was correlated with CEC (0.62*), total P‐NaHCO₃ (‐0.83**) and P‐HCl (0.76**), while CEC was correlated with P‐resin (‐0.70**), total NaHCO₃ (‐0.88**) and P‐HCl (0.94**).     

EFFECT OF FOLIAR APPLICATION OF UREA,MOLYBDENUM, BENZYLADENINE,SUCROSE AND SALICYLIC ACID ON YIELD,NITROGEN METABOLISM OF RADISH PLANTS AND QUALITY OF EDIBLE ROOTS

In 2006–2007 small radish was cultivated in a pot experiment. Foliar applications were applied twice with solutions of the following compounds: 1) control (water); 2) urea; 3) urea+molybdenum (Mo), 4) urea+Mo+benzyladenine (BA); 5) urea+Mo+BA+sucrose; 6) urea+Mo+BA+sucrose+salicylic acid (SA), 7) BA; 8) SA; and 9) sucrose. The above solutions contained following concentrations of compounds: urea 20 g dm^?3, sucrose 10 g dm^?3, Mo 1 mg dm^?3, BA 5 mg dm^?3 and SA 10 mg dm^?3. In comparison with the control, spraying plants with the solution of urea+Mo+BA+sucrose and SA only caused an increase in leaf mass of one plant. Foliar applications did not have any effect on the yield of edible roots. When compared with the control, the use of sucrose resulted in a decreased content of nitrate (V) in leaves, while the application of urea+Mo+BA+sucrose led to elevated content of nitrate (V) in roots. In case of spraying plants with solutions containing urea (combinations no. 2–6) there was a tendency to increase ammonium (NH₄ ⁺) and nitrogen (N)-total content in leaves and roots, and increase in N uptake by leaves and by the whole plant but not by the radish roots. In combinations 7–9 we noted a decline in the level of ascorbic acid, and in combinations 2–6 there was a decrease in the content of soluble sugars in roots. In comparison with the control, an increase was observed in combinations 2 and 3, while in combinations 7–9 a decrease in the content of free amino acids in roots was observed. None of the combinations with foliar application caused any significant changes in the content of assimilative pigments in radish leaves and concentration of nitrate (III), dry matter in leaves and roots, the content of phenolic compounds, content of potassium (K), magnesium (Mg), calcium (Ca) extracted with 2% acetic acid in roots as well as free radical activity of radish roots.     

Effects of pretreatment and solution chemistry on solubility of rice‐straw phytoliths

Rice is a Si‐accumulator plant, whereby Si has physio‐chemical functions for plant growth. Its straw contains high shares of plant silica bodies, so‐called phytoliths, and can, when returned to the soil, be an important Si fertilizer. Release of Si from phytoliths into soil solution depends on many factors. In order to improve prognosis of availability and management of Si located in phytoliths, in this study we analyzed the effect of pretreatment of rice straw by dry and wet ashing and the soil‐solution composition on Si release. Dry ashing of rice straw was performed at 400°C, 600°C, and 800°C and wet ashing of the original straw and the sample from 400°C treatment with H₂O₂. To identify the impact of soil‐solution chemistry, Si release was measured on separated phytoliths in batch experiments at pH 2–10 and in presence of different cations (Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺) and anions (Cl^–, NO$ _3^- $ , SO$ _4^{2-} $ , acetate, oxalate, citrate) in the concentration range from 0.1 to 10 mmol_c L^–1. After burning rice straw at 400°C, phytoliths and biochar were major compounds in the ash. At an electrolyte background of 0.01 mol_c L^–1, Si released at pH 6.5 was one order of magnitude higher than at pH 3, where the zeta potential (ζ) was close to zero. Higher ionic strength tended to suppress Si release. The presence of cations increased ζ, indicating the neutralization of deprotonated Si‐O^– sites. Monovalent cations suppressed Si release more strongly than bivalent ones. Neutralization of deprotonated Si‐O^– sites by cations might accelerate polymerization, leading to smaller Si release in comparison with absences of electrolytes. Addition of Al³⁺ resulted in charge reversal, indicating a very strong adsorption of Al³⁺, and it is likely that Si‐O‐Al‐O‐Si bonds are formed which decrease Si release. The negative effect of anions on Si release in comparison with deionized H₂O might be due to an increase in ionic strength. The effect was more pronounced for organic anions than for inorganic ones. Burning of rice straw at low temperatures (e.g., 400°C) appears suitable to provide silicon for rice in short term for the next growing season. High inputs of electrolytes with irrigation water and low pH with concomitant increase of Al³⁺ in soil solution should be avoided in order to keep dissolution rate of phytoliths at an appropriate level.     

Phosphorus fractions and profile distribution in newly formed wetland soils along a salinity gradient in the Yellow River Delta in China

Soil P availability has been identified as one of the key factors controlling wetland productivity, structure, and function. Soil P fractions at different depths in newly formed wetlands along a salinity gradient in Yellow River Delta (China) were studied using a modified Hedley fraction method. The total P (P_t) content ranged from 471.1 to 694.9 mg kg^–1, and diluted HCl‐extractable inorganic P (Dil‐HCl‐P_i) ranged from 324 to 524.2 mg kg^–1. The Dil‐HCl‐P_i is the predominant P form in all profiles, with on average 70% of the P_t extracted as P_i. Organic P (P_o) comprised (4.2 ± 2.0)% (mean ± SD) of the P_t, due to low organic‐matter content in coastal salt marsh ecosystems. The labile P (resin‐P, NaHCO₃‐P_i, and NaHCO₃‐P_o) and moderately labile P (NaOH‐P_i and NaOH‐P_o) concentrations were both low, ranged from 11.6 to 38.1 and 2.8 to 21.3 mg kg^–1, respectively, constituting (3.7 ± 1.1)% and (2.0 ± 0.7)%, respectively, of P_t, suggesting low availability of P to plants in these soils. Our results suggested that vegetation cover significantly influenced soil P dynamics and availability. In particular, the labile P content under Tamarix chinensis increased significantly by 23.2%–145.5% compared with adjacent soils. These findings have important implications for wetland conservation or restoration and long‐term sustainable management of newly formed wetland ecosystems in the Yellow River Delta.     

Analysis of Proton Generation and Consumption of Forest Surface Soils in Hokkaido, Northern Japan

We determined proton budgets of surface soils in a deciduous forest (Df) and a coniferous forest (Cf) of Volcanogenous Regosols in Tomakomai, Hokkaido of northern Japan. The total H⁺ source was 12.9 and 11.6 kmol_c ha^?1 y^?1 at Df and Cf respectively, and the external H⁺ was 1% at Df and 2% at Cf. The primary H⁺ sources were vegetation uptake of base cations and nitrification, while the major H⁺ sinks were release of base cations and NO₃ ⁺ uptake by vegetation. Leaching incubation experiments using A horizon soils including Df and Cf with NH₄ ⁺ solutions (5.3, 15.9 mg N L^?1) showed that H⁺ from nitrification was generally higher in the Df soil than Cf soil, and nitrification of Tomakomai Df soil was the highest in both treatments. Results of multiple regression analyses suggested that pH_kCl and exchangeable Ca²⁺ contributed to the H⁺ generation via nitrification. Leaching experiments with dilute HCl (pH 3.3) revealed that cation release (mainly Ca²⁺) occurred, and the proportion of release by decrease of exchangeable cations was higher than that by mineral weathering. Mineral weathering in the Tomakomai soil was higher than the other soils.