Variable silicon content of rice cultivars grown on everglades histosols 1

Two experiments were conducted to investigate silicon (Si) content in a group of rice cultivars. Ten cultivars were grown in the greenhouse under three levels pf Si fertilization on a Si‐deficient Histosol. In a second experiment, 18 ‘cultivars were grown at three field locations which varied in plant‐available soil Si. In both experiments, cultivars varied in their percentage of Si in rice straw. There was no significant (P > 0.10) genotype by environment interaction. The genotypes with the greatest and lowest percentage of Si were consistently so over all Si environments and treatments.     

Isoproturon mineralization in an agricultural soil

The impact of soil moisture content and temperature on isoproturon (3-(4-isopropylphenyl)-1,1-dimethyl-urea [IPU]) mineralization activity was assessed on an agricultural soil regularly exposed to this herbicide. Mineralization of ¹⁴C-IPU was monitored on soil microcosms incubated at different temperatures (10°C, 20°C, 28°C) and soil moisture contents (9%, 12%, 15, 18%, 21%, 24%). An increase in temperature and/or soil moisture significantly enhanced the maximum rate and percentage of IPU mineralization while it decreased the lag time before mineralization. The maximum rate and percentage of IPU mineralization respectively ranged from 0.18% day⁻¹ and 9% for the lowest temperature and soil moisture content pair (10°C–9%) to 1.51% day⁻¹ and 27.1% for the highest pair (28°C–24%). Statistics revealed a cross interaction of temperature and soil moisture content on the maximum rate of IPU mineralization. The optimum conditions for IPU mineralization, estimated from the double Gaussian model, were 25.8°C and 24% soil moisture content. The influence of fluctuations in soil moisture content on IPU-mineralization was investigated by subjecting the soil microcosms to drought stress. When IPU was added at the end of the drought stress, it had no statistical effect on IPU mineralization. However, when it was added before the drought stress, two mineralization phases were observed: (1) one corresponding to the drought stress for which mineralization was low and (2) another one observed after restoration of soil moisture content characterized by higher mineralization rate. It can be concluded that climatic fluctuations affect the activity of IPU mineralizing microbial community, and may lead to an increase in IPU persistence.     

Nitrogen mineralization of leguminous crops in soils

Organic‐N production by legumes is a key benefit of growing cover crops and green manures. A soil sample was mixed with legume residue commonly used as green manure in Kenya at a rate of 500 mg N (kg soil)^–1. Silica sand equal to the weight of the soils was added and mixed thoroughly. The mixture was packed in a leaching tube and leached with 100 mL of 5 mM of CaCl₂ ^. 2H₂O and incubated at 30°C. The leaching was repeated every 2 weeks for a total of 16 weeks and analyzed for N as NH , NO , and NO . Five legume residues and five different soils were used in this study. Nitrogen mineralization of the legume residues conformed to an exponential model. Application of a two‐components exponential model showed two phases of N mineralization. The relationship between the organic N remaining after each incubation period and time of incubation was controlled by two first‐order reactions. The initial fast rate (k₁) changed to a slow rate (k₂) at incubation times ranging from 2 to 8 weeks, depending on the legume residue and the soil used. The percentage of N in each phase varied among the legume residue and soils. Linear regression analyses showed that net cumulative amounts of N mineralized from individual legume residues was significantly correlated with the total polyphenols and polyphenol‐to‐N ratios for two soils. Nitrogen mineralization of dolichos and field bean was significantly and negatively correlated with clay and sand, respectively; of field bean and alfalfa was significantly correlated with C_mic; and of dolichos significantly but negatively correlated with the total N and organic N in soils. Linear regression analysis of the pooled data showed that net cumulative amounts of N mineralized and percentage N mineralized were significantly correlated with C : N ratios of the residues (r = 0.44 and 0.48 at p < 0.05, respectively), and that net cumulative N mineralized was significantly correlated with (lignin + polyphenols)‐to‐N ratios (r = 0.41 at p < 0.05) and with lignin contents (r = 0.61 at p < 0.001).     

Temperature sensitivity of nitrogen mineralization in agricultural soils

As concerns continue to mount over nitrogen (N) use efficiency and the fate of excess N lost to the environment, the need for accurate assessments of the contribution of non-fertilizer sources is increasing. Nitrogen mineralization from soil organic matter (SOM) can supply large quantities of plant-available N through a growing season and is affected by numerous factors including soil temperature and soil properties. The objective of this study was to determine the temperature sensitivity of N mineralization in soils under annual crops in California and to determine whether growing region and soil properties affect the temperature sensitivity of N mineralization. Nitrogen mineralization was assessed for 55 soils from different regions in central and northern California by incubating undisturbed soil cores at 5, 15, and 25 °C for 10 weeks. Modeling was done by fitting the data to both an S-shaped curve and a Q₁₀ function. Q₁₀ values averaged 2.87 and ranged from 2.67 to 3.15 in the different regions. While the magnitude of N mineralized varied greatly, the temperature response did not differ significantly across regions and was not affected by SOM content and quality, texture, electrical conductivity, or pH. Coupling the temperature response curve with daily soil temperature data measured in the field highlighted the differences in regional and seasonal mineralization rates and underscored the importance of taking soil temperature into account when determining N mineralization rates for N budgets. This is especially important in regions where crops are grown year-round.     

Nitrogen mineralization in the field at various soil depths

The accumulation of mineral nitrogen was measured in the field in five soil-layers between 0 and 120 cm, in two plots of a long-term experiment contrasting high and low fertilizer inputs. Soil temperature and moisture were also determined. The total quantity of mineral N that accumulated in the 0-120 cm soil layer during 11 weeks in the summer was 138 and 78 kg ha⁻¹, 25% and 45% of which were found below 60cm, in the high and the low fertility plots, respectively. Nitrogen mineralization in the field was predicted by a model which takes account of changes in temperature and moisture content of the soil. The potentially mineralizable N for this model was found from laboratory incubation experiments. The measured amount of mineralized N was 13 to 26% less than the predicted amount.     

Nitrogen mineralization and nitrate reduction in forests

The mineralization of soil nitrogen was studied in four forests growing on krasnozem soils. Soils from Silver Wattle (Acacia dealbata Link.) and Mountain Ash (Eucalyptus regnans F. Muell.) forests showed considerable nitrification in laboratory incubations. Messmate (Eucalyptus obliqua L'Herit) and Monterey Pine (Pinus radiata D. Don) forest soils were predominantly ammonifiers. Forests having significant soil nitrification were found to have considerable nitrate reductase activity (NRA) in root or leaf tissue or both. NRA may therefore be useful as an indication of soil nitrification in natural ecosystems. The occurrence of nitrification in Australian forests appears to be predominantly related to the amount of N present and its rate of turnover rather than to inhibitory effects.     

Phosphorus mineralization in subarctic agricultural and forest soils

Summary Potential P and C mineralization rates were determined in a 12-week laboratory incubation study on subarctic forest and agricultural soil samples with and without N fertilizer added. There was no significant difference in net inorganic P produced between N fertilized and unfertilized soils. The forest soil surface horizons had the highest net inorganic P mineralized, 32 mg P kg^-1 soil for the Oie and 17 mg P kg^-1 soil for the Oa. In the cropped soils net inorganic P immobilization started after 4 weeks and lasted through 12 weeks of incubation. Cumulative CO₂–C evolution rates differed significantly among soils, and between fertilizer treatments, with the N-fertilized soils evolving lower rates of CO₂–C than the unfertilized soils. Soils from the surface horizons in the forest evolved the highest rates of CO₂–C (127.6 and 89.4 mg g^-1 soil for the Oie and Oa horizons, respectively) followed by the cleared uncropped soil (42.8 mg g^-1 soil C), and the cropped soils (25.4 and 29.0 mg g^-1 soil C). In vitro soil respiration rates, or potential soil organic matter decomposition rates, decreased with increasing time after clearing and in accord with the degree of disturbance. Only soils with high potential C mineralization rates and high organic P to total P ratios, mineralized P by the end of the study. Mineralizable P appeared to be associated with readily mineralizable organic C.     

云南主要植烟土壤不同土层氮矿化研究

为了解云南不同植烟土壤类型土壤的供氮能力,在主要植烟区选择紫色土、水稻土和红壤3种土壤分层采集土样,室内20℃和30℃条件下培养,应用间歇淋洗好气培养法测定氮矿化量。结果表明,不同土壤类型的氮矿化累积量在表层0～20 cm和亚表层20～40 cm表现为紫色土氮矿化强度较大,氮矿化累积量较高,红壤相对较低,而在60～80 cm和80～100 cm土层以水稻土氮矿化累积量最高,紫色土最低。不同土层土壤以0～20 cm土层氮矿化速率和矿化量最高,其次是20～40 cm土层,再次是40～60 cm土层,最低的是60～80 cm土层和80～100 cm土层。随着培养时间延长,土壤中的氮矿化量随之降低。30℃条件下的土壤氮矿化速率和矿化量高于20℃条件。     

Nitrogen mineralization in coal mine spoil and topsoil

Summary N mineralization was compared in fresh topsoil, stockpiled topsoil, coal-mine spoil, and in various mixtures of soil and mine spoil, with and without sludge amendment. N mineralization was slightly lower in stockpiled topsoil than in fresh topsoil or mine spoil. Differences between stockpiled and fresh topsoil were small and were attributed to changes in the relative proportions of readily degradable versus slowly degradable organic fractions. Sludge amendment increased N mineralization, but straw amendment immobilized N through 12 weeks of incubation. More N was leached from mixtures of mine spoil and soil than from soil or mine spoil alone, but net N mineralization decreased with increasing mine-spoil-to-soil ratios, probably as a result of greater denitrification losses. Mixing mine spoil with soil can increase plant available N more than soil or spoil alone, because spoil contributes mineralizable organic N while soil improves the physical and chemical environment of the mine spoil.     

华中地区旱地氮素矿化的能力

Nitrogen mineralization potentials of 15 soil samples were studied by the methods of soil aerobic incubation, and the correlation between the potentials and the amounts of nitrogen taken up by rye grass (Lolium multiflorum Lam.) in pot culture was calculated. The soils were collected from Hubei Province in Central China. Soil nitrogen mineralization potentials (N_O) were calculated and optimized by a quick-BASIC program. N_O ranged from 60 mg kg^-1 to 340 mg kg^-1, which accounted for 9.1% to 34.6% of the total nitrogen content. Among the examined soils, yellow-brown soil collected from Wuhan had the largest N_O and brown-red soil from Xianning had the smallest one. The mineralization rate constants (k) ranged from 0.00556 d^-1 to 0.01280 d^-1, in average 0.00882 d^-1. Chao soil from Wuhan had the greatest k while yellow-cinnamon soil from Zhaoyang had the smallest one. There were apparent differences between mineralization parameters (N_O and k) optimized and non-optimized ones. Optimized N_O had a better correlation than non-optimized N_O with the amount of nitrogen accumulated in the aerial parts of rye grass. N_O, N_O × k and N_t(accumulated mineralized nitrogen within time t) could be used as indexes of soil nitrogen supply. Among them N_t was the best, which was significantly correlated with the amounts of nitrogen accumulated in the aerial parts of rye grass harvested at three different times.     

Nitrogen mineralization and assimilation at millimeter scales

This study used inoculated, artificial soil microcosms containing sand, clay, cellulose, and localized “hotspots” of highly labile, organic N-containing dead bacteria to study N mineralization and assimilation at millimeter scales. Labeling with ¹⁵NH₄⁺ along with measurement of its assimilation into microbial biomass at the bulk scale allowed estimation of gross rates of ammonification and N assimilation using isotope dilution. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of transects of organic-¹⁵N across Si wafers in contact with the microcosms indicated strong gradients of ¹⁵NH₄⁺ assimilation as a function of proximity to the hotspots that were not apparent using bulk analyses. This combination of bulk and ToF-SIMS analyses represents a powerful approach to explore the physical and biochemical factors that affect N process heterogeneities in soils.     

Nitrogen mineralization as affected by cropping system

Abstract

The quantity of crop residues returned to the soil is controlled by the cropping system and in turn these residues affect the amount of mineral nitrogen (N) released by decomposition of organic matter. This study was conducted to evaluate the effect of four 20‐year‐old cropping systems which returned varying amounts of crop residue on N mineralization potential (N₀) of a Misteguay silty clay soil. N₀ was estimated from a long‐term incubation study using exponential and hyperbolic models. The N₀ ranges from 70 to 109 mg.kg^‐1 for the exponential model and 86 to 144 mg.kg^‐1 for the hyperbolic model. Values of N₀ are closely related to the estimated amount of crop residue returned. It requires 0.33 Mg.ha^‐1 of crop residue returned to increase N₀ one mg.kg^‐1. Estimated N₀ values are consistently greater for the hyperbolic than for the exponential model. However, there is a close relationship between the instantaneous rates of reaction of the two models suggesting both models can be used in laboratory incubation studies to estimate N₀ using a nonlinear least‐squares fitting technique. This study shows that the exponential and hyperbolic models are equally effective in distinguishing both the qualitative and quantitative changes in soil organic N due to the cropping system in place.     

Nitrogen mineralization in a coarse soil of the semi-arid Pampas of Argentina

Use of the nitrogen balance sheet method as a fertilization strategy in the semi-arid Pampas of Argentina is restricted because of a lack of available information regarding nitrogen mineralization in its coarse soils. Our objective was to determine nitrogen mineralization during corn (Zea mays L.) and following wheat (Triticum aestivum L.) growing cycles under contrasting tillage systems in a representative soil of the region. Mineralized nitrogen from decomposing residues was estimated using the litter bag method and mineralization from soil organic matter using a mass balance approach. Soil water content was higher under no-till during the corn growing season and no differences were detected for wheat during this period. Soil temperature was practically not affected by tillage system. Biomass and nitrogen absorption were higher under no-till than under disk till in corn (p ≤ 0.05), as were nitrogen mineralization from residues and organic matter (p ≤ 0.05). In wheat, no differences in biomass, nitrogen absorption and mineralization were detected between treatments. Mineralization during crop growing cycles accounted for 44.8–67.5% of the absorbed nitrogen. Differences in nitrogen mineralization between tillage systems resulted from the greater water availability under no-till than under disk till during the summer.     

Nitrogen mineralization and water-table height in oligotrophic deep peat

Summary Peat cores, 0–60 cm depth, were taken on 14 occasions from three experimental plots where the water levels in the surrounding ditches had been artificially controlled for 14 years at 0, 20 and 50 cm below the surface. Numbers of aerobic and anaerobic ammonifying bacteria in the profile were significantly increased (P< 0.05) by lowering the water level from 0 to 50 cm. These increases occurred mainly in the surface 20 cm horizon, where 80%–90% of the ammonifying bacteria in the profile occurred. Mineral N in fresh samples, which was present almost entirely as ammonium, decreased sharply with depth below 20 cm, and on two occasions concentrations were significantly greater (P<0.05) in plots with water levels at 20 and 50 cm than in the flooded peat. Readily mineralized N, produced during waterlogged incubation at 30°C for 9 weeks, was significantly greater (P<0.05) on eight occasions in samples from plots with water levels at 20 or 50 cm than in those where the water level was at the surface. Calculations showed that the increases in N availability as a result of lowering the water-table could be attributed mainly to deeper rooting.     

Nitrogen compounds in soil solutions of agricultural land

Plants are capable of taking up nitrogen (N) in both organic and inorganic forms, so the concentrations and relative proportions of different N forms in soils are likely to be important determinants of their N nutrition. Therefore, there is a need for greater knowledge of the N profiles of soils. In the study presented here we examined the potential plant-available N in soils from four sites with various agricultural histories (one recently fertilized), using small tension lysimeters to collect free and bound amino acids and inorganic N forms in solution, with minimal soil disturbance and with intact plants present. Subsequent analysis showed that concentrations of free amino acids ranged from 0.1 to 12.7 μM, whereas concentrations of bound amino acids were on average 50 times higher, and higher than ammonium and nitrate concentrations in all three unfertilized soils. In contrast, nitrate strongly dominated in the fertilized soil. Bound amino acids are likely to represent a potential replenishment pool for free amino acids, so the abundance and rate at which amino acid-containing substances are depolymerized might be important determinants of the availability of free amino acids. Our results highlight the need for further research on the liberation of free amino acids from polymers in agricultural soil, and the importance of bound amino acids as N sources for plants.     

Carbon and nitrogen mineralization in subarctic agricultural and forest soils

Summary C and N mineralization potentials were determined, in a 12-week laboratory incubation study, on soil samples obtained from recently cleared land which had been cropped to barley for 4 years (field soils) and from nearby undisturbed taiga (forest soils). Treatments for the cropped soils were conventional and no-tillage with and without crop residues removed. An average of about 3% of the total C was evolved as CO₂ from the field soils compared with > 10% and 4% for the upper (Oie) and lower (Oa) forest-floor horizons, respectively. Significantly more C was mineralized from the Ap of the no-till treatment with residue left on the surface than from the other field Ap horizons. Both forest-floor horizons showed rather long lag periods for net mineralization compared with the field soils, but at the end of the incubation, more mineral N was recovered from the forest Oie despite a rather wide C:N ratio, than from the field soils. After 12 weeks about 115, 200 and 20 g mineral N/g soil were recovered from the field Ap, the forest Oie and the forest Oa horizons, respectively. Very little C or N was mineralized from the B horizon of the forest or the field soils. Nitrification was rapid and virtually complete for the field soils but was negligible for both forest-floor O horizons.Paper no J-188 of the Journal Series of the Alaska Agricultural and Forestry Experiment Station     

我国主要植烟土壤氮素矿化潜力研究

为研究我国植烟土壤潜在供氮能力及其分布状况,从18个烤烟主产省的317个县采集了500多个土壤样品,采用Stanford的间歇淋洗好气培养法,测定了土壤氮素矿化势和矿化速率常数。结果表明,植烟土壤氮素矿化速率常数（k）平均为0.017/d,土壤氮素矿化势（No）平均为130.6 mg/kg,变幅为5.5～372.0 mg/kg,0—30 cm土壤累积潜在供氮量达到了470.2 kg/hm2。不同植烟区土壤矿化势差异显著,黄淮烟区、北部西部烟区、东北烟区、南部烟区、长江中上游烟区、长江中下游烟区、西南烟区土壤矿化势的分别为:64.1、78.8、99.0、119.9、127.8、135.0 和160.5 mg/kg。其中南方烟区（南部烟区、长江中上游烟区、长江中下游烟区、西南烟区）的矿化势显著高于北方烟区（北部西部烟区和东北烟区）和黄淮烟区。不同类型土壤矿化势存在显著差异,即使是同一类型土壤,其矿化势变异仍很大。因此应从宏观上把握全国植烟土壤的供氮潜力,对于土壤供氮潜力过高的区域,在植烟土壤区划中应考虑进行调整,而对较高的区域,可以考虑采用农艺措施进行调控,减少烟株生育后期氮素供应;而对于土壤供氮适量的区域,应作为优先发展烤烟生产的区域。     

农业部发展战略研究中心专题项目

我国土地塌陷面积大，数量多，以年均6万hm^2增加，地表塌陷改变了农业生态体系，安徽省淮北市烈山塌陷区在主体开发水产的同时，以资源为依托，以市场为导向，进行了种、养、加、绿化相结合的综合性开发，实现了良性循环的高效生态农业，为全面开发塌陷区开辟了有效途径。     

The influence of organic nitrogen mineralization on the management of agricultural systems in the UK

Abstract. The understanding of nitrogen mineralization is central to providing good advice to ensure that nitrogen (N), from whatever source, is utilized by crops as efficiently as possible to minimize pollution. We have reviewed how mineralization is accounted for in current advice. It is clear that there is at least a qualitative understanding of the effects of soil and crop management on N mineralization and N supply, which has enabled the development of Codes of Good Agricultural Practice and fertilizer recommendations systems, based on sound scientific principles. However, to refine advice there is a need for a better quantitative understanding. Although soil organic matter (SOM) is a major source of N for crops, we are unable adequately to predict fertilizer requirement as affected by mineralization of SOM. Nitrogen returns from crop residues can vary considerably between fields; the provision of better field specific advice is restricted by our inability accurately to quantify this variability. The qualitative controls on the amount and timing of N release from ploughed grass are known, but better quantification of mineralization/immobilization over both the short- and long-term and better understanding of the relationship with sward age, inputs and management are essential. Much N can also be released from pasture and lost to the environment, especially where long-term leys have been grazed and there is a need to quantify the changing balance of mineralization and immobilization with the age of sward and N input. Whilst the overall principle of cultivation affecting mineralization is well known and appreciated, little is known about the mechanisms and quantification is only possible for a comparison of such extremes as ploughing and direct drilling.