Nitrate Concentrations In Soil Solution Research Articles

Use of a Portable Rapid Analysis System to Measure Nitrate Concentration of Nutrient and Soil Solution, and Plant Sap in Greenhouse Vegetable Production

A rapid analysis ion-selective electrode (ISE) system for measurement of [NO3−] in nutrient solution (NS), soil solution (SS) and petiole sap (PS) was evaluated. For each material, there were 797–2010 samples from 5 to 6 different crops, and from 2 to 4 different species. Accuracy was evaluated by linear regression (LR) with laboratory analysis (automated colorimetry, Cd reduction), and by relative error (RE), the average percentage deviation from laboratory analysis. For NS, the LR was y = 0.982x + 0.76, R² = 0.962 (n = 2010), for combined data from 5 crops (3 pepper, 2 cucumber). For SS, the LR was y = 0.975x + 1.13, R² = 0.965 (n = 797), for combined data from 5 crops (3 pepper, 2 cucumber). For undiluted PS, the LR relationship was y = 0.742x + 168.02, R² = 0.892 (n = 1425), for combined data from 6 crops (3 pepper, 2 cucumber, 1 melon). The underestimation was most pronounced at [NO3−] of >1500 mg NO3−–N L−1. For diluted petiole sap (dilution by 10 for pepper and melon, 5 for other species), the LR relationship was y = 1.010x + 99.26, R² = 0.927 (n = 1182), for combined data from 6 crops (2 pepper, 2 cucumber, 1 melon, 1 tomato). RE values for all measurements in composite datasets were 14%, 22%, 24% and 25% for NS, SS, undiluted PS and diluted PS respectively, and they were lower in concentrations most likely to be measured in practical on-farm work. The ISE system measured [NO3−] in NS, SS and diluted PS with sufficient accuracy to effectively guide on-farm decision making.

Simulation of nitrate and potassium concentrations in soil solution using parametric models and Hydrus-2D

This study estimated the nitrate and potassium concentration in the soil solution of drainage lysimeter using the mathematical models developed by Vogeler et al. (1996) and Muñoz-Carpena et al. (2005) and the computational model Hydrus-2D, while comparing the simulated and observed data using statistical parameters. The cultivar used for the study was ‘Prata Gorutuba’. The experimental plots were six lysimeters of drainage. Fertigation was performed weekly. The mathematical models developed by Vogeler et al. (1996) and Muñoz-Carpena et al. (2005) were used to determine the specific concentration of a given ion (Ci). The Hydrus software was used to simulate the dynamics of nutrients. The concentrations of nitrate and potassium in the soil solution were estimated by the model of Vogeler et al. (1996), adapted to the linear type CEw-Ci ratio and simulated by the Hydrus model, resulting in an acceptable characterization of the distribution of these nutrients.

Soil and Nutrient Cycling Responses in Riparian Forests to the Loss of Ash (Fraxinus spp. L) from Emerald Ash Borer (Agrilus planipennis, Fairmaire)

Emerald ash borer (EAB) is an alien invasive species that is spreading across Canada and the United States killing ash trees. In riparian forests where ash may be abundant; loss of ash can induce significant structural changes; including the creation of canopy gaps; changes in light penetration; expansion of ground vegetation; and alteration of soil nitrogen and carbon cycling. In 2014 and 2015, we examined the effects of EAB-caused gaps in riparian forests on soil nutrient dynamics. Two sites with different infestation timelines, a “new” site (mortality in past 2–3 years) and an “old” site (infested 10 years previous) were selected to determine temporal differences in effects of canopy gaps created by ash loss on litterfall, herbaceous ground vegetation, and soil nutrient cycling. Within both sites, plots with clustered dead ash (canopy gap plots—CG) were paired with nearby plots of full canopy and no ash (canopy closed plots—CC), and differences between paired plots determined. Total litterfall was observed at all sites but was only significant at the new infestation site. Reductions in leaf litter deposition in CG plots resulted in reduced N and C flux to the forest floor but soil C and N concentrations, and nitrogen mineralization rates, were not significantly different between CG and CC plots. Nitrate concentration in soil solution was significantly greater in CG plots compared to CC plots at the new infestation sites but showed the opposite trend at the old infestation sites. Herbaceous ground vegetation biomass was significantly greater (up to 10×) in CG plots than in CC plots. Overall, despite changes to riparian forest canopy structure and litterfall, there was no significant difference in soil nutrient cycling between EAB-induced canopy gaps and closed canopy plots after 10 years, suggesting a high resilience of riparian forest soils to EAB infestation

Band application of acidified slurry as an alternative to slurry injection in Mediterranean winter conditions: Impact on nitrate leaching

The aim of the present work was to assess the impact of raw slurry injection and band application of acidified slurry upon nitrate leaching in two different soils under Mediterranean conditions. A lysimeter experiment with a winter crop (oat - Avena sativa) was performed over three years presenting significant inter-annual precipitation variability. Four fertilization treatments using dairy cattle slurry were implemented. Nitrate leaching was estimated using nitrate concentration in soil solution assessed through ceramic suction cups and drainage calculated using the Agricultural System Root Zone Water Quality Model (RZWQM2). Results show that the RZWQM2 was able to predict drainage with an average efficiency of 89%. Cumulative drainage averaged 69 and 65% of the precipitation for the sandy and the sandy loam soils, respectively. The application of acidified slurry did not lead to any increase of nitrate leaching relative to band application or injection of raw slurry. Soil incorporation following soil application of acidified slurry is highly relevant regarding nitrate leaching since it significantly reduced nitrate leaching in more than 50% in the sandy soil and close to 40% in the sandy loam soil. A severe risk of pollution swapping was observed with slurry injection since it led to an increase of nitrate leaching relative to band application of raw or acidified slurry (more than 100% in the sandy soil and around 30% in the sandy loam soil for the rainiest year). According to the results, band application of acidified slurry is an efficient alternative to raw slurry injection to minimize nitrogen losses by leaching. Nevertheless, soil incorporation of acidified slurry, not necessary in terms of ammonia emissions, is strongly recommended to reduce nitrate leaching.

Nitrogen deposition increases N2O emission from an N-saturated subtropical forest in southwest China

Nitrous oxide (N2O) is a major greenhouse gas, with elevated emission being reported from subtropical forests that receive high nitrogen (N) deposition. After 10 years of monthly addition of ammonium nitrate (NH4NO3) or sodium nitrate (NaNO3) to a Mason pine forest at Tieshanping, near Chongqing city in Southwest China, the simulated N deposition was stopped in October 2014. The results of soil N2O emissions monitoring in different seasons during the nitrogen application period showed that nitrogen addition significantly increased soil N2O emission. In general, the N2O emission fluxes were positively correlated to nitrate (NO3−) concentrations in soil solution, supporting the important role of denitrification in N2O production, which was also modified by environmental factors such as soil temperature and moisture. After stopping the application of nitrogen, the soil N2O emissions from the treatment plots were no longer significantly higher than those from the reference plots, implying that a decrease in nitrogen deposition in the future would cause a decrease in N2O emission. Although the major forms of N deposition, NH4+ and NO3−, had not shown significantly different effects on soil N2O emission, the reduction in NH4+ deposition may decrease the NO3− concentrations in soil solution faster than the reduction in NO3− deposition, and thus be more effective in reducing N2O emission from N-saturated forest soil in the future.

Biomass Production and Environmental Considerations from Reed Canarygrass Fertilized with Organic Residues in Northern Environments

Core Ideas Liquid swine manure and municipal biosolid provide sufficient N for reed canarygrass.Liquid swine manure and municipal biosolid use do not cause nitrate leaching and heavy metal accumulation.Kura clover with reed canarygrass improves DM yield but less than fertilizers. Sustainable biomass production on marginal lands of northern areas using cool‐season perennial grasses and under‐exploited N sources requires development. We determined the biomass production of reed canarygrass (Phalaris arundinacea L.) fertilized with municipal biosolid (MB), liquid swine manure (LSM), mineral fertilizer (M), or grown with a legume species and harvested either in July or October along with the consequences of soil contamination by nitrates and heavy metals. The experiment, conducted at two sites from 2009 to 2011, included three target N rates (40, 80, and 120 kg total N ha−1) applied in spring as either MB, LSM, or M along with an unfertilized control treatment and a treatment with kura clover (Trifolium ambiguum M. B.). Reed canarygrass responded positively to N application from all sources. Both sources of organic fertilization resulted in DM yield close to that obtained with mineral fertilization but seasonal DM yield was greater with LSM than with MB. Kura clover improved DM yield compared with reed canarygrass without N fertilization, but it was not sufficient to reach DM yields obtained with N fertilization. The three N sources did not affect residual soil nitrates in the fall at both sites, the soil solution nitrate concentrations measured during the growing season at one site, nor the soil accumulation of heavy metals (Cu, Zn, and Cd) in the fall of the last year at both sites. Our results confirm that, as an alternative to M use, MB and LSM are valuable N sources for reed canarygrass biomass in northern areas.

Waterlogging and soil reduction affect the amount and apparent molecular weight distribution of dissolved organic matter in wetland soil: a laboratory study

The release of dissolved organic matter (DOM) from wetland soils is an important pathway for the input of organic compounds into adjacent aquatic environments. In the present study we investigated, under controlled laboratory conditions, the quantity and quality of DOM released from a wetland soil subject to waterlogging and reducing conditions. Three soil redox conditions (oxic, moderately reducing and advanced reducing) were distinguished based on nitrate, ferrous ions and sulfate concentrations in soil solution. Under each redox condition, the quantity (dissolved organic carbon (DOC), humic substances and peptides plus proteins (P-PN) and quality (aromaticity; specific ultraviolet absorbance at 254 nm (SUVA254nm)) and apparent molecular weight (aMW) distribution) of DOM were investigated. The results showed that soil redox condition affects the amount and properties of mobilised DOM. The rate of DOM release and SUVA254 values were highest during the transition from oxic to moderately reducing conditions, whereas both stabilised during progression to advanced reducing conditions. In addition, the mobilised DOM is expected to be more reactive because of an increase in polar substituents in aromatic structures between oxic and moderately reducing conditions. During the development of moderately reducing conditions, dissolved humic substances increased significantly, whereas their aMW distribution (between 500 and 6000 ) remained constant for each of the three different redox conditions. In contrast, the quantity of dissolved P-PN remained low and steady under the three redox conditions, whereas the aMW distribution of protein-like and microbial by-product-like compounds decreased during the development of reducing conditions (aMW of compounds between 100 and >100 000).

Seasonal dynamics of nitrate and ammonium ion concentrations in soil solutions collected using MacroRhizon suction cups

The aims of the study were to analyse the concentration of nitrate and ammonium ions in soil solutions obtained using MacroRhizon miniaturized composite suction cups under field conditions and to determine potential nitrogen leaching from soil fertilized with three types of fertilizers (standard urea, slow-release urea, and ammonium nitrate) at the doses of 90 and 180 kg ha−1, applied once or divided into two rates. During a 3-year growing experiment with sugar sorghum, the concentration of nitrate and ammonium ions in soil solutions was the highest with standard urea fertilization and the lowest in variants fertilized with slow-release urea for most of the months of the growing season. Higher concentrations of both nitrogen forms were noted at the fertilizer dose of 180 kg ha−1. One-time fertilization, at both doses, resulted in higher nitrate concentrations in June and July, while dividing the dose into two rates resulted in higher nitrate concentrations between August and November. The highest potential for nitrate leaching during the growing season was in July. The tests confirmed that the miniaturized suction cups MacroRhizon are highly useful for routine monitoring the concentration of nitrate and ammonium ions in soil solutions under field conditions.

Mechanisms behind plant diversity effects on inorganic and organic N leaching from temperate grassland

Higher plant diversity reduces nitrate leaching by complementary resource use, while its relation to leaching of other N species is unclear. We determined the effects of plant species richness, functional group richness, and the presence of specific functional groups on ammonium, dissolved organic N (DON), and total dissolved N (TDN) leaching from grassland in the first 4 years after conversion from fertilized arable land to unfertilized grassland. On 62 experimental plots in Jena, Germany, with 1–60 plant species and 1–4 functional groups (legumes, grasses, tall herbs, small herbs), nitrate, ammonium, and TDN concentrations in soil solution (0–0.3 m soil layer) were measured fortnightly during 4 years. DON concentrations were calculated by subtracting inorganic N from TDN. Nitrogen concentrations were multiplied with modeled downward water fluxes to obtain N leaching. DON leaching contributed most to TDN leaching (64 ± SD 4% of TDN). Ammonium leaching was unaffected by plant diversity. Increasing species richness decreased DON leaching in the fourth year. We attribute this finding to enhanced use of DON as a C and N source and enhanced mineralization of DON by soil microorganisms. An increase of species richness decreased TDN leaching likely driven by the complementary use of nitrate by diverse mixtures. Legumes increased DON and TDN leaching likely because of their N\(_{2}\)-fixing ability and higher litter production. Grasses decreased TDN leaching because of more exhaustive use of nitrate and water. Our results demonstrate that increasing plant species richness decreases leaching of DON and TDN.

Modelling impacts of acid deposition and groundwater level on habitat quality and plant species diversity

We quantified the effects of the site factors pH and nitrate (NO3) concentration in soil solution and groundwater level on the vegetation of terrestrial ecosystems for the Netherlands in response to changes in atmospheric nitrogen (N) and sulphur (S) deposition and groundwater level over the period 1990–2030. The assessment was made with the SMART2 model, a simple one-layer model including geochemical buffer processes, element cycling by litterfall, mineralisation and uptake, nitrogen transformation processes and element input through deposition, weathering and upward seepage. To assess the effects of changes in abiotic site factors on the vegetation, we developed a simple plant diversity indicator for grassland, heathland and forest, based on the occurrence of target plant species and competing species. Species occurrence was calculated from the preferred ranges of each species for the NO3 concentration and pH in soil solution and mean spring groundwater level. Changes in the plant diversity indicator were assessed from effects of changes in the occurrence of target and competing plant species in response to changes in mean spring groundwater level and in pH and NO3 concentration, as calculated with SMART2. Calculations were made for combinations of five vegetation structure types (three forest types, semi-natural grassland and heathland) and seven soil types (three sandy soils, two clay soils, peat and loess soils) using a 250 × 250 m grid. We used data for atmospheric deposition and groundwater level in the past to assess trends between 1990 and 2010 and evaluated two future scenarios for the period 2010–2030: a Business as Usual and an Improved Environment scenario. Comparison of model predictions on pH and NO3 with measured soil solution concentrations for forest showed a reasonable to good agreement for pH but rather poor for NO3. The largest impacts were found for the combination of the two Improved Environment scenarios. Reductions in N and S deposition and an increase in groundwater level between 1990 and 2030 hardly caused changes in soil pH and only relatively small reductions in NO3 concentration (11–13%). Nevertheless, those changes caused a significant increase in plant diversity indicator.

Agro-environmental sustainability of different water management practices in temperate rice agro-ecosystems

Water management practices alternative to continuous flooding are highly required to enhance water use efficiency and safeguard environmental quality in temperate rice agro-ecosystems. In this work, we carried out a two year field experiment (2012⿿2013) in a rice paddy in NW Italy to evaluate and quantify the agro-environmental sustainability of three different water management practices involving (i) water seeding and continuous flooding (WFL), (ii) dry seeding and flooding at tillering stage (DFL), and (iii) dry seeding and intermittent irrigation (DIR). The effects of water management on agronomic parameters, such as crop yields, yield components and the apparent N recovery were evaluated for four rice varieties (Gladio, Baldo, Selenio e Loto) representing the main Italian grain types. We also evaluated net irrigation, water use efficiency, nitrate leaching and runoff, and greenhouse gas (GHG) emissions for the different management practices. Water management strongly affected grain yields and qualitative yield components. Whereas WFL and DFL showed similar yields, DIR resulted in significant yield reductions by 28, 24, 19 and 14% for the four varieties, respectively. This was related to a lower tillering rate, and reduced N uptake and apparent fertilizer N recovery. Intermittent irrigation however showed lowest net irrigation and consequently a higher water use efficiency (56%) with respect to WFL (22%) and DFL (26%). High soil solution nitrate concentrations and leaching from the root zone as a result of nitrification under oxic soil conditions represented the greatest environmental constrain of dry seeded cropping systems. On the other hand, water management practices alternative to continuous flooding, in particular DIR, strongly contributed to mitigate GHG emissions and reduce the Global Warming Potential of these cropping systems by up to 70⿿90%.

Criteria of Nitrate Concentration in Soil Solution and Leaf Petiole Juice for Fertigation of Cucumber under Greenhouse Cultivation in Gyeonggi region

To develop a technique for efficient management of fertility for cucumber in greenhouse, a quick test method to quantify nitrate (NO₃ - ) content in soil solution and leaf petiole juice using a simple instrument that are easy to use for farmers was investigated. N fertilizer (urea) was applied at 0, 50, 100 and 200% levels of the recommended application rate from 30 days after transplanting to harvest by soil fertigation treatments. Stable results were obtained from analysis of nitrate (NO₃ - ) using top 10 t h or 11 th leaf petioles collected between 10 to 11 am in the morning. Under the semiforcing culture, NO₃ - content of leaf petiole juice was highest at 60 days after transplanting (DAT) at all fertigation treatments. Appropriate NO₃ - content of leaf petiole juice was 2,418±78～2,668±118 at 45 DAT, 3,032±90～3,332±63 at 60 DAT, 2,709±50～3,158±155 at 75 DAT, 2,535±49～2,907±83 at 90 DAT, and 2,242±48 ㎎ L -1 at 105 DAT. In addition, appropriate NO₃ - content of soil solution was 167±9～212±15 at 45 DAT, 83±10～112±12 at 60 DAT, 49±3～92±6 at 75 DAT, 71±9～103±9 at 90 DAT, and 73±9 ㎎ L -1 at 105 DAT. The cucumber yield at 100% N level of fertigation was 7,770 ㎏ 10a -1 and no difference in yield was found at 200% N level of fertigation. However, there was 12% decrease in yield at 50% N fertigation and, 17% decrease at 0% N fertigation. Under retarding culture, NO₃ - concentration of leaf petiole juice was highest at 55 days after transplanting (DAT) at all fertigation treatments. Appropriate NO₃ - content of leaf petiole juice was 2,464±102～2,651±33 at 45 DAT, 3,025±71～3,314±84 at 55 DAT and 2,488±92 ㎎ L-1 at 65 DAT, respectively. Appropriate NO₃ - content of soil solution was 111±10～155±14 at 45 DAT, 93±7～147±14 at 55 DAT, 67±4 ㎎ L -1 at 65 DAT, respectively. The cucumber yield at 50% N fertigation was not different from 1,697 ㎏ 10a -1 of 100% N fertigation level and even with that of the 200% N fertigation. However, there was 21% decrease in yield at 0% N fertigation.

The effect of stocking rate on soil solution nitrate concentrations beneath a free-draining dairy production system in Ireland

Economically viable and productive farming systems are required to meet the growing worldwide need for agricultural produce while at the same time reducing environmental impact. Within grazing systems of animal production, increasing concern exists as to the effect of intensive farming on potential N losses to ground and surface waters, which demands an appraisal of N flows within complete grass-based dairy farming systems. A 3-yr (2011 to 2013) whole-farm system study was conducted on a free-draining soil type that is highly susceptible to N loss under temperate maritime conditions. Soil solution concentrations of N from 3 spring-calving, grass-based systems designed to represent 3 alternative whole-farm stocking rate (SR) treatments in a post-milk quota situation in the European Union were compared: low (2.51 cows/ha), medium (2.92 cows/ha), and high SR (3.28 cows/ha). Each SR had its own farmlet containing 18 paddocks and 23 cows. Nitrogen loss from each treatment was measured using ceramic cups installed to a depth of 1m to sample the soil water. The annual and monthly average nitrate, nitrite, ammonia, and total N concentrations in soil solution collected were analyzed for each year using a repeated measures analysis. Subsequently, and based on the biological data collated from each farm system treatment within each year, the efficiency of N use was evaluated using an N balance model. Based on similar N inputs, increasing SR resulted in increased grazing efficiency and milk production per hectare. Stocking rate had no significant effect on soil solution concentrations of nitrate, nitrite, ammonia, or total N (26.0, 0.2, 2.4, and 32.3mg/L, respectively). An N balance model evaluation of each treatment incorporating input and output data indicated that the increased grass utilization and milk production per hectare at higher SR resulted in a reduction in N surplus and increased N use efficiency. The results highlight the possibility for the sustainable intensification of grass-based dairy systems and suggest that, at the same level of N inputs, increasing SR has little effect on N loss in pastoral systems with limited imported feed. These results suggest that greater emphasis should be attributed to increased grass production and utilization under grazing to further improve the environmental impact of grazing systems.

Effect of Nitrogen Application Levels on Nitrate Concentration in Soil Solution under Plastic Film House

This study was conducted to investigate investigated the effect of nitrogen fertilizer on nitrate concentration in soil solution and to determine the relationship between yield and nitrate concentration in soil solution for cucumber cultivation under plastic film house. Nitrogen as urea was applied at rates of 0, 120, 240, 360, and <TEX>$480kg\;N\;ha^{-1}$</TEX> as an additional fertilizer by trickle irrigation during cucumber cultivation. Monitoring of nitrate concentration in soil solution was investigated using porous cups at 25 cm depth under soil surface. Nitrate concentration in soil solution increased with increasing the rate of additional nitrogen. Correlation coefficient between EC value and nitrate concentration was positive in soil and soil solution (p<0.05). An additional nitrogen of about <TEX>$300kg\;ha^{-1}$</TEX> was shown the highest yield of cucumber, and improved yield by 5% compared to N recommendation of <TEX>$240kg\;N\;ha^{-1}$</TEX>. The highest yield was determined at nitrate concentration of <TEX>$82mg\;L^{-1}$</TEX> in soil solution by regression equation (<TEX>$Y=74.2+0.73X+0.000504X^2$</TEX>, <TEX>$R^2=0.629^*$</TEX>). These results means indicate that nitrate concentration in soil solution would be useful method to rapid determination for additional nitrogen during cucumber cultivation under plastic film house.

토양용액 채취를 위한 토성별 한계수분함량 설정

Soil moisture is an important factor for the availability and circulation of nutrients in arable soil. The purpose of this study was to set thresholds moisture content on soil nitrate concentration in the solution for real-time diagnosis. Sandy loam, silt loam, and sandy loam was filled with <TEX>$1.2g\;cm^{-3}$</TEX> at Wagner pots, 0, 100, and <TEX>$200mg\;L^{-1}$</TEX> of <TEX>$KNO_3$</TEX> was saturated. Nitrate in standard solution was recovered about 95% by passing the porous cup. Nitrate concentrations in sampling of soil solution were examined by using a porous cup. The soil solution was higher in accordance with sandy loam> silt loam> clay loam, limited water filled pore space for sampling soil solution was 33.7, 56.4, and 62.2%, respectively. Nitrate concentration in the soil solution was negligible at sandy loam and silt loam during sampling periods, which was decreased about 50~82% in clay loam compared to the initial <TEX>$NO_3$</TEX>-N concentration in the saturated <TEX>$KNO_3$</TEX> solution. Over limitation of soil solution sampling, soil EC and <TEX>$NO_3$</TEX>-N content were increased with the saturated <TEX>$NO_3$</TEX>-N concentration, regardless of soil texture (p<0.05). Conclusively, soil solution by using a porous cup was possible, regardless of the soil texture, which was useful for the diagnosis in nitrate concentration of soil solution. However, because nitrate concentration of soil solution in a clay loam changes, it was necessary for careful attention in order to take advantage for the real-time diagnosis of nitrogen management in soil.

Ion-Selective Electrode Offers Accurate, Inexpensive Method for Analyzing Soil Solution Nitrate in Remote Regions

Nitrogen (N) applied as fertilizer is subject to runoff and leaching. Nitrate (NO3−-N) concentrations in soil solution reflect the impacts of farm management on N cycling. Some of the most remote regions in the world are undergoing rapid land-use change, yet there are major barriers to conducting research in these locations. Fortunately, new tools such as ion-selective electrodes (ISEs) provide low-cost and simple methods for conducting chemical analysis in the field. Researchers compared soil solution NO3−-N concentrations measured using an ISE with concentrations measured on a colorimeter (cadmium reduction) and found good agreement (r2 = 0.96, P < 0.0001) between the two methods. The ISE is also 66 times less expensive than in-country laboratory analysis or shipping and analyzing the samples in the United States. Thus, the ISE is an excellent tool for rapid analysis of N in soil solution, providing critical information on N dynamics in remote regions.

ALUMINUM SPECIATION OF AMENDED ACID TROPICAL SOIL AND ITS EFFECTS ON PLANT ROOT GROWTH

Exchangeable and soluble soil aluminum (Al) is limiting plant growth in many soils worldwide. This study evaluated the effects of increasing rates of dolomite and magnesium carbonate (MgCO3) on Al3+, pH, dissolved organic carbon, cations, anions, and Al speciation on oil palm Deli dura × AVROS pisifera root growth. Dolomite and MgCO3 additions significantly raised linearly soil solution pH, magnesium (Mg2+), nitrate (NO3 −) and chlorine (Cl−) concentrations; exponentially decreased the activity of phytotoxic Al species [aluminum (Al3+), aluminum sulfate (Al2SO4), and aluminum fluoride (AlF3)]; and reduced manganese (Mn) concentration and activity. High activity of those species exponentially reduced root dry weight. Optimum oil palm growth was achieved at: <50 μM monomeric Al, < 30 μM Mn, and <0.20 unit of the ratio Al+Mn to calcium (Ca)+Mg. High activity of Al species and Mn in acidic soil solution cause significant reduction of the root growth. Soil acidity alleviation either with dolomite or MgCO3 mitigates the toxic effect of Al and Mn.

Increased inorganic nitrogen leaching from a mountain grassland ecosystem following grazing removal: a hangover of past intensive land-use?

Heathlands and grasslands occur in montane regions, naturally or due to anthropogenic land-use. These are typically nutrient-poor but exposure to elevated nitrogen deposition and intensive livestock grazing causes large-scale ecological change. We studied the long-term implications of grazing removal on soil and drainage water biogeochemistry and the implications for nitrogen cycling in 50-year replicated grazing exclosures on a montane grassland exposed to high rates of ambient nitrogen deposition. Evidence of ‘ecosystem recovery’ represented by successional change from graminoid to shrub-dominance after cessation of grazing was not reflected in the soil biogeochemistry. Cessation of grazing had a negative impact, with increased soil extractable and soil solution nitrate concentrations; an apparent shift towards a more nitrogen-rich, bacterially dominated microbial community; and the acidification of soils and leachate. The increase in nitrate leaching appears to have been counterbalanced by a decrease in dissolved organic nitrogen leaching, approximately maintaining the overall nitrogen balance of the system, whilst apparently altering ecosystem functioning. High rates of organic matter cycling and inorganic nitrogen uptake in grazed grassland may have sustained ecosystem N limitation under elevated nitrogen deposition. Grazing removal caused long-term over-supply of nitrogen from mineralisation of enriched organic matter, exacerbated by continued high nitrogen deposition, exceeding the uptake demand of heath vegetation and resulting in nitrification and nitrate leaching. This disequilibrium between vegetation and soil following grazing removal has implications for restoration after periods of intensive grazing. Grazing may not simply leave a legacy of nutrient enrichment but its cessation may trigger nitrogen saturation and soil and freshwater eutrophication and acidification which counteract the immediate benefits of natural vegetation recovery. Long term, nitrogen saturation of abandoned grasslands is likely to reduce ecosystem resilience to invasion by nitrophilous species, pathogen attack and vulnerability to environmental pressures such as climate change. We conclude that partial and/or phased reduction in grazing levels may permit the more synchronised recovery of soils and vegetation, thereby avoiding imbalances between nitrogen supply and nitrogen demand and detrimental ecological effects.

Nitrate leaching through climatologic water balance in a fertigated coffee plantation

Nitrate losses from soil profiles by leaching should preferentially be monitored during high rainfall events and during irrigation when fertilizer nitrogen applications are elevated. Using a climatologic water balance, based on the models of Thornthwaite and Penman Monteith for potential evapotranspiration, drainage soil water fluxes below the root zone were estimated in a fertigated coffee crop. Soil solution extraction at the depth of 1 m allowed the calculation of nitrate leaching. The average nitrate concentration in soil solution for plots that received nitrogen by fertigation at a rate of 400 kg ha-1, was 5.42 mg L-1, surpassing the limit of the Brazilian legislation of 10.0 mg L-1, only during one month. For plots receiving 800 kg ha-1 of nitrogen, the average was 25.01 mg L-1, 2.5 times higher than the above-mentioned limit. This information indicates that nitrogen rates higher than 400 kg ha-1 are potentially polluting the ground water. Yearly nitrate amounts of leaching were 24.2 and 153.0 kg ha-1 for the nitrogen rates of 400 and 800 kg ha-1, respectively. The six times higher loss indicates a cost/benefit problem for coffee fertigations above 400 kg ha-1.

Effects of over-winter green cover on soil solution nitrate concentrations beneath tillage land

There is a growing need to reduce nitrogen losses from agricultural systems to increase food production while reducing negative environmental impacts. The efficacy of vegetation cover for reducing nitrate leaching in tillage systems during fallow periods has been widely investigated. Nitrate leaching reductions by natural regeneration (i.e. growth of weeds and crop volunteers) have been investigated to a lesser extent than reductions by planted cover crops. This study compares the efficacy of natural regeneration and a sown cover crop (mustard) relative to no vegetative cover under both a reduced tillage system and conventional plough-based system as potential mitigation measures for reducing over-winter soil solution nitrate concentrations. The study was conducted over three winter fallow seasons on well drained soil, highly susceptible to leaching, under temperate maritime climatic conditions. Mustard cover crop under both reduced tillage and conventional ploughing was observed to be an effective measure for significantly reducing nitrate concentrations. Natural regeneration under reduced tillage was found to significantly reduce the soil solution nitrate concentrations. This was not the case for the natural regeneration under conventional ploughing. The improved efficacy of natural regeneration under reduced tillage could be a consequence of potential stimulation of seedling germination by the autumn reduced tillage practices and improved over-winter plant growth. There was no significant effect of tillage practices on nitrate concentrations. This study shows that over winter covers of mustard and natural regeneration, under reduced tillage, are effective measures for reducing nitrate concentrations in free draining temperate soils.