Unfertilized Plots Research Articles

Chemical changes in organic matter after fungal colonization in a nitrogen fertilized and unfertilized Norway spruce forest

Background and aimsDecomposition and transformation of organic matter (OM) in forest soils are conducted by the concomitant action of saprotrophic and mycorrhizal fungi. Here, we examine chemical changes in OM after fungal colonization in nitrogen fertilized and unfertilized soils from a Norway spruce forest.MethodsSand-filled bags amended with composted maize leaves were placed in the forest soil and harvested after 17 months. Infrared and near edge X-ray absorption fine structure spectroscopies were used to study the chemical changes in the OM. Fungal community composition of the bags was also evaluated.ResultsThe proportion of ectomycorrhizal fungi declined in the fertilized plots, but the overall fungal community composition was similar between N treatments. Decomposition of the OM was, independently of the N level or soil horizon, accompanied by an increase of C/N ratio of the mesh-bag content. Moreover, the proportions of carboxylic compounds in the incubated OM increased in the mineral horizon, while heterocyclic-N compounds decreased, especially in unfertilized plots with higher N demand from the trees.ConclusionsOur results indicate that more oxidized organic C and less heterocyclic-N proportions in the OM remain after fungal colonization in the mineral layers, and suggest that ectomycorrhizal fungi transfer less heterocyclic-N from the mesh bags to the host trees under high N levels.

Soil carbon and nitrogen dynamics as affected by land use change and successive nitrogen fertilization of sugarcane

Abstract The land use change (LUC) and application of N fertilizers have potential to affect soil C and N dynamics and long–term C and N stocks. We aimed to evaluate the effects of the LUC from native vegetation (seasonal semideciduous forest) to sugarcane (Saccharum spp.) cultivation under successive annual N fertilizer applications on chemical and microbiological attributes of sugarcane–cropped soils. Two field trials were performed during three (Site 1) or four years (Site 2) in southeastern Brazil. Soil sampling was carried out in the following N treatments applied to the crop: control (N–unfertilized plots), organomineral fertilizer (100 kg ha−1 yr−1 N), and synthetic fertilizer (100 and 200 kg ha−1 yr−1 N). Soil samples from native vegetation located near each site were also taken, to serve as reference for studying LUC. For Site 1, successive application of N fertilizers on sugarcane managed under green cane trash blanketing system maintained the C and N dynamics and stocks in soil to conditions similar to those found before LUC. At Site 2, however, modifications in soil attributes caused by LUC were more impacting than the N fertilization management. Compared to synthetic N fertilizers, successive application of organomineral fertilizer did not improve the soil microbiological attributes as well as organic C and total N stocks. Lastly, successive high N input (200 kg ha−1 yr−1, via synthetic fertilizer) promoted accumulation of mineral N deep in the soil profile, thus increasing potential losses through NO3− leaching.

Soil nitrogen availability indices as predictors of sugarcane nitrogen requirements

Abstract Nitrogen recommendation systems for sugarcane (Saccharum spp.) generally does not consider the N supply from soil. Identifying a reliable soil test for estimating N availability is crucial to avoid yield losses or environmental pollution. Therefore, the objective of this study was to correlate and calibrate N availability indices with field–based measures of soil N supply. Between 2006 and 2013, 15 trials for rate–response to N fertilizer by sugarcane ratoons were performed in Sao Paulo, the main sugarcane–producing state in Brazil. The following indices were tested: KMnO4 oxidizable C, hot KCl extractable N, phosphate–borate buffer distillable N, NaOH distillable N, Illinois Soil N Test, organic C, total N, mineral N, anaerobic incubation, soil respiration, substrate–induced respiration, microbial biomass C, metabolic quotient, microbial quotient, and gross N mineralization. The indices were then correlated with sugarcane yield (Y0N) and N content of the crop (N0N) in N–unfertilized plots, relative yield (RY), and the N rate predicted to achieve 90% of the RY (NR 90%RY). Although weak correlations were found between Y0N with anaerobic incubation, total N, and soil respiration, as well as between N0N and anaerobic incubation, no index correlated with RY or NR 90%RY. Grouping sites based on soil texture or byproduct management did not improve prediction of RY. Therefore, we concluded that none of the fifteen laboratory indices is a reliable predictor of soil N supply, and hence could not be used to adjust N fertilization rate for sugarcane.

Occurrence of poorly responsive soils in western Kenya and associated nutrient imbalances in maize (Zea mays L.)

A poor response to fertilizer application is one of the persisting constraints preventing closure of the maize yield gaps in Sub-Saharan Africa (SSA). It is speculated that nutrient imbalances derived from deficient and/or excessive concentrations could be one of the causes of this limited response of maize to fertilizer. This is however not confirmed and the extent of such poor response is ill-documented. To investigate this, we conducted 44 on-farm trials with a two treatment structure (with and without NPK fertilizer) in two subsequent seasons, the 2014 long rains (LR) and short rains (SR) distributed across two sites: Bungoma-Southwest and Busia-North in western Kenya. As a discriminating criterion between responsive and poorly responsive soils, we used a Value Cost Ratio (VCR) of 2 of NPK fertilizer use. Nutrient sufficiency ranges were developed using compositional nutrient diagnosis (CND method) and then used to identify both deficient and/or excessive nutrient concentrations occurring in maize grown in the poorly responsive soils.Results show that 48% of all fields from both sites could be classified as ‘poorly responsive’, with small VCR values ranging between 0.1 and 1.99. Nutrient deficiencies were more prevalent than situations of excessive concentrations in such fields. N-deficiency was the most common in the unfertilized (control) plots occurring in between 80 and 89% of the poorly responsive plots. Zn-deficiency became apparent in the fertilized plots and was observed at similar frequencies in this treatment. The next most widespread nutrient deficiencies in poorly responsive soils were those of P and Cu affecting between 70 and 79% of both control and fertilized plots. K and Mg deficiencies were rare in both treatments. This study indicates that the occurrence of poorly responsive soils in Bungoma-southwest and Busia-North is likely related to micronutrient deficiencies. These findings necessitate further investigation on the bioavailability of these micronutrients nutrients in such soils and a validation trial to evaluate the extent of crop responses.

Historical trends in iodine and selenium in soil and herbage at the Park Grass Experiment, Rothamsted Research, UK

AbstractLong‐term trends in iodine and selenium retention in soil, and uptake by herbage, were investigated in archived samples from the Park Grass Experiment, initiated in 1856 at Rothamsted, UK. Soil (0–23 cm) and herbage samples from plots receiving various mineral fertilizers and organic manures, with and without lime, were analysed for selenium (Se) and iodine (I) to assess the effect of soil amendments, annual rainfall, crop yield and changes in soil chemistry from 1876 to 2008. Comparing soil from limed and unlimed control (unfertilized) plots, TMAH‐extractable Se and I concentrations both diverged, with time, with greater retention in unlimed plots; differences in concentration amounted to 92 and 1660 μg/kg for Se and I, respectively, after 105 yr. These differences were broadly consistent with estimated additions from rainfall and dry deposition. Offtake of both elements in herbage was negligible compared to soil concentrations and annual inputs (<0.003% of total soil I and <0.006% of total soil Se). A positive correlation was observed between I and Se concentrations in herbage, suggesting some common factors controlling bioavailability. A growth‐dilution effect for I and Se was suggested by the positive correlation between growing season rainfall (GSR) and herbage yield together with soil‐to‐plant transfer factors decreasing with yield. Phosphate and sulphate fertilizers reduced I and Se herbage concentrations, both through ion competition and increased herbage yield. Results suggest that in intensive agriculture with soil pH control, the I requirement of grazing animals is not likely to be met by herbage alone.

Mitigating Global Warming Potential and Greenhouse Gas Intensities by Applying Composted Manure in Cornfield: A 3-Year Field Study in an Andosol Soil

A 3-year study was conducted in cornfield to evaluate how composted cattle manure application affects net global warming potential (GWP; the sum of nitrous oxide (N2O) and methane (CH4) minus net ecosystem carbon balance (NECB)) and greenhouse gas intensity (GHGI; net GWP per unit of plant biomass yield). In the first experiment, conducted from 2010 to 2012, five fertilization strategies that included an unfertilized control plot, inorganic fertilizer-only plot, two plots with inorganic fertilizer plus composted cattle manure, and composted cattle manure-only plot were established. In the second experiment composted cattle manure was applied in autumn 2012 and the field was subdivided into three plots in spring 2013, with one plot receiving additional composted cattle manure, the second plot received additional inorganic fertilizer and the third plot did not receive any additional fertilization. Fluxes of N2O, CH4 and CO2 were measured using the static closed chamber method. NECB was calculated as carbon (C) inputs minus C output (where a negative value indicates net C loss). In experiment 1, manure application significantly increased NECB and reduced net GWP by more than 30% in each of the three years of the study. GHGI in the manure-amended plots was lower than in other plots, except in 2012 when the manure-only plot had higher GHGI than fertilizer-only plot. Application of inorganic fertilizer alone increased GWP by 5% and 20% in 2010 and 2011, but showed a 30% reduction in 2012 relative to the unfertilized control plot. However, due to higher net primary production (NPP), fertilizer-only plot had lower GHGI compared to the control. Application of inorganic fertilizer together with manure showed the greatest potential to reduce GWP and GHGI, while increasing NPP and NECB. In experiment 2, additional manure or inorganic fertilizer application in spring increased NPP by a similar amount, but additional manure application also increased NECB, and decreased GWP and GHGI. Manure application, as a partial substitute or supplemental fertilizer, shows potential to mitigate GWP and GHGI.

Plant Secondary Metabolites in Alfalfa, Birdsfoot Trefoil, Reed Canarygrass, and Tall Fescue Unaffected by Two Different Nitrogen Sources

Plant secondary metabolites (PSM) may increase the sustainability of agriculture systems by reducing inputs, as PSM protect plants against herbivores and pathogens, act as pesticides, insecticides, and anthelmintics while also attracting pollinators and seed dispersers. Therefore, it is important to understand what affects PSM fluctuation in plant tissues. Limited research has investigated how different nitrogen (N) sources affect PSM concentration in alfalfa (Medicago sativa L., Alf), birdsfoot trefoil (Lotus corniculatus L., BFT), reed canarygrass (Phalaris arundinacea L., RCG), and endophyte‐infected tall fescue (Festuca arundinacea Schreb., E+TF). We investigated how fecal manure (feces) and synthetic N fertilizer (urea, 46% H2NCONH2) influence N concentrations and the PSM ergovaline, gramine, saponins, and extractable condensed tannins (CT) in E+TF, RCG, Alf, and BFT, respectively. Ergovaline, saponins, and CT were not affected by fertilization. Gramine tended (P = 0.06) to be greater in control plots than in fertilized plots. Total N in E+TF and RCG was greater (P < 0.05) and tended to be greater for Alf (P = 0.08) in synthetically fertilized plots than in unfertilized plots. Seasonal variation in PSM and N was significant (P < 0.003) across all species and was species specific. Total N in E+TF was greatest in June (41.4 g kg−1), while ergovaline contents were at the lowest values recorded (117.2 μg kg−1), with subsequent increases to the greatest ergovaline values observed in July (680.0 μg kg−1). Our results reveal the variability in PSM production by plants and highlight the complexities of predicting fluctuations of PSM in forages. As environments where plants grow vary through space and time, we recommend studies on a case‐by‐case basis, depending on land management objectives.

Soil Carbon and Nitrogen Responses to Nitrogen Fertilizer and Harvesting Rates in Switchgrass Cropping Systems

The environmental sustainability of bioenergy cropping systems depends upon multiple factors such as crop selection, agricultural practices, and the management of carbon (C), nitrogen (N), and water resources. Perennial grasses, such as switchgrass (Panicum virgatum L.), show potential as a sustainable bioenergy source due to high yields on marginal lands with low fertilizer inputs and an extensive root system that may increase sequestration of C and N in subsurface soil horizons. We quantified the C and N stocks in roots, free particulate, and mineral-associated soil organic matter pools in a 4-year-old switchgrass system following conversion from row crop agriculture at the W.K. Kellogg Biological Station in southwest Michigan. Crops were fertilized with nitrogen at either 0, 84, or 196 kg N ha−1 and harvested either once or twice annually. Twice-annual harvesting caused a reduction of C and N stocks in the relatively labile roots and free-particulate organic matter pools. Nitrogen fertilizer significantly reduced total soil organic C and N stocks, particularly in the stable, mineral-associated C and N pools at depths greater than 15 cm. The largest total belowground C stocks in biomass and soil occurred in unfertilized plots with annual harvesting. These findings suggest that fertilization in switchgrass agriculture moderates the sequestration potential of the soil C pool.

CO2 Emissions from Tropical Peat Soil Affected by Fertilization

The conversion of peat soils to agricultural uses has been thought to increase CO2 emission due to several factors, including fertilization. However, evidence on the effect of fertilization on CO2emissionsfrompeat soils is rareand often inconsistence. We measured the effects of different types of fertilizer, including N, P and K sources, and clay as an ameliorant on CO2 emission from a bare peat soil in Lubuk Ogong, Riau Province. Nutrients were added in the following combinations: 0 (unfertilized plot), N source (urea), slow-release N (slow release urea), N and Psource (Urea+SP-36), N, P and K sources (urea+SP-36+KCl) and combined NPK-Clay. Fertilization resulted in a decreasein CO2 emissions compared to that prior to fertilization except when slow-release urea was applied. Decreasing of CO2 emissions was probably due to pH-related effects because the pH in the N treatment was lower than in both the control and the unfertilized plot. A decreasein the level of CO2 emissions among the treatments followed the order NPK-Clay>NP>NPK>urea>slow-release urea. Covariance analyses showed that the difference in CO2 emissions prior to treatment was not significant. The application of individual and combined treatments of N, P, K and NPK mixed with 5 Mg ha-1 clay led to significantly reduced CO2 emissions from bare peat soil in Lubuk Ogong, Riau Province. In addition to fertilization, the water table depth was the only parameter that significantly affected the CO2 emissions (P<0.05). We conclude that the application of nutrient combinations, including N, P, K and clay, could reduce CO2 emissions because these treatments maintain a balanced nutritional condition in the soil with respect to the microbial activity.Keywords: Amelioration, CO2 emission, fertilization, tropical peat soils

Anaerobically Incubated Nitrogen Improved Nitrogen Diagnosis in Corn

Core Ideas Traditional corn N diagnostic methods (pre‐plant nitrate N test and pre‐sidedress nitrate N test) only account for mineral N. Objective: to improve N diagnostic methods by considering N mineralization. Pre‐plant nitrate N test and pre‐sidedress nitrate N test were improved by anaerobic‐N (Nan) in areas with similar soil/climates. Models combining Nan, texture and temperature improved pre‐plant nitrate N test and pre‐sidedress nitrate N test in all areas. Current N diagnostic methods for corn (Zea mays L.) are often based on the nitrate nitrogen (NO3−–N) concentration before planting (pre‐plant nitrate test, PPNT) and nitrate nitrogen (NO3−–N) concentration at V6 stage (PSNT). These tests provide scant information on soil N mineralization during the growing season, which can supply a considerable proportion of corn N requirements. The objective of our study was to evaluate if in‐season N recommendations could be improved by inclusion of a N mineralization potential estimator. We conducted field experiments (n = 35) in three different areas and in two planting dates. At each site we evaluated PPNT, PSNT, and NH4–N released during anaerobic incubation (Nan), which were then related to corn yield in unfertilized plots (0N) and corn response to nitrogen fertilization (Nresp%) using multiple regression analysis. The sole incorporation of Nan to PPNT and PSNT models improved their capacity to predict corn yield in 0N plots and Nresp% only in areas with similar edaphic‐climatic characteristics. Independently of the geographical region, when PPNT and PSNT were combined with Nan, texture, and temperature, their capacity to predict yield in 0N plots was increased (PPNT: from R2 0.02–0.47; PSNT: from R2 0.09–0.53), as it was their capacity to estimate Nresp% (PPNT: from R2 0.06–0.23; PSNT: from R2 0.19–0.42). The inclusion of Nan can improve traditional N diagnostic models when it is combined with edaphic/climatic properties that account for the mineralization rate of this N pool.

One century of Nordic barley breeding: nitrogen use efficiency, agronomic traits and genetic diversity

SUMMARYThe current study aimed to evaluate breeding effect on nitrogen use efficiency (NUE), its components and some agronomic traits and disease resistance in barley by using extensive germplasm covering 72 landraces and 123 cultivars released since 1910. Trials were established in southern Finland with a modified strip-plot experimental design. Prior to sowing, blocks were placement fertilized with compound nitrogen : phosphorus : potassium (NPK) fertilizer (N-P-K: 20–3–8) at the rate of 35 and 70 kg N/ha and unfertilized plots were placed at the other end of the fertilization block. The germplasm collection was genotyped with 1536 single nucleotide polymorphism (SNP) markers and phenotyped during a 2-year field experiment in 2011/12. Independent of row type, a positive breeding effect was evident in NUE and for other plant N traits, except that grain N slightly decreased. Breeding has improved NUE by 0·08 kg/year (26% over the century). Nitrogen utilization and N uptake efficiencies were also improved by breeding as were straw length, lodging tolerance, grain yield and yield components, without any sign of levelling-off. Bred cultivars were more resistant to leaf-damaging diseases, especially to net blotch. The SNP data indicated no reduction in overall genetic diversity. However, genetic diversity differed along the barley chromosomes showing either reduced or increased diversity in certain regions when landraces were compared with modern varieties.

Nitrogen supply effect on emmer (Triticum dicoccum Schübler) ecophysiological and yield performance

The effects of nitrogen (N) addition on productive and physiological traits of Triticumdicoccum were assessed under two N levels (0, unfertilized, and 90 kg N ha−1) in fieldconditions, in two growing seasons. In the study case, the N supply (90 kg N ha−1) was appliedin three-split applications (20% at pre-plant stage, 40% at tillering stage, 40% at stemelongation). In unfertilized conditions, the productive and physiological traits were consistentlyreduced in comparison with fertilized treatments. Indeed, control plots showed lowergrain yield, biomass and protein content (about 42, 44 and 19%, respectively) and lowerphotosynthetic activity at light saturation level (25%) than fertilized plots. The stomatalconductance was 34.2% and 70.8% lower in unfertilized plots than in fertilized those, in the firstand second year, respectively. No significant differences for the Ci/Ca ratio were evidentbetween treatments. Emmer physiological and yield performances were affected by N supply,although the crop plasticity to N availability was emphasized.

Changes in litter quality induced by nutrient addition alter litter decomposition in an alpine meadow on the Qinghai-Tibet Plateau.

The effects of nitrogen (N) and phosphorus (P) addition on litter decomposition are poorly understood in Tibetan alpine meadows. Leaf litter was collected from plots within a factorial N × P addition experiment and allowed to decompose over 708 days in an unfertilized plot to determine the effects of N and/or P addition on litter decomposition. Results showed that nutrient addition significantly affected initial P and P-related biochemical properties of litter from all four species. However, the responses of litter N and N-related biochemical properties to nutrient addition were quite species-specific. Litter C decomposition and N release were species-specific. However, N and P addition significantly affected litter P release. Ratios of Hemicellulose + Cellulose to N and P were significantly related to litter C decomposition; C:N ratio was a determinant of litter N release; and C:P and (Hemicellulose + Cellulose):P controlled litter P release. Overall, litter C decomposition was controlled by litter quality of different plant species, and strongly affected by P addition. Increasing N availability is likely to affect litter C decomposition more indirectly by shifting plant species composition than directly by improving litter quality, and may accelerate N and P cycles, but shift the ecosystem to P limitation.

Bioenergy cropping systems that incorporate native grasses stimulate growth of plant-associated soil microbes in the absence of nitrogen fertilization

The choice of crops and their management can strongly influence soil microbial communities and their processes. We used lipid biomarker profiling to characterize how soil microbial composition of five potential bioenergy cropping systems diverged from a common baseline five years after they were established. The cropping systems we studied included an annual system (continuous no-till corn) and four perennial crops (switchgrass, miscanthus, hybrid poplar, and restored prairie). Partial- and no-stover removal were compared for the corn system, while N-additions were compared to unfertilized plots for the perennial cropping systems. Arbuscular mycorrhizal fungi (AMF) and Gram-negative biomass was higher in unfertilized perennial grass systems, especially in switchgrass and prairie. Gram-positive bacterial biomass decreased in all systems relative to baseline values in surface soils (0–10cm), but not subsurface soils (10–25cm). Overall microbial composition was similar between the two soil depths. Our findings demonstrate the capacity of unfertilized perennial cropping systems to recreate microbial composition found in undisturbed soil environments and indicate how strongly agroecosystem management decisions such as N addition and plant community composition can influence soil microbial assemblages.

Temperature sensitivity of soil organic carbon decomposition as affected by long-term fertilization under a soybean based cropping system in a sub-tropical Alfisol

Understanding temperature sensitivity of soil organic carbon (SOC) decomposition from bulk soils and aggregates of long-term fertilized plots is imperative to forecast soil C dynamics. We evaluated the impacts of 43 years of fertilization under a soybean (Glycine max) based cropping system on temperature sensitivity of SOC decomposition (Q10) in an Alfisol. Treatments were: no mineral fertilizer or manure (control), 100% recommended dose of nitrogen (N), N and phosphorus (NP), N, P and potassium (NPK), NPK+lime at 0.4Mgha−1 (NPK+L), 150% recommended NPK (150% NPK), and NPK+farmyard manure (FYM) at 10Mgha−1 (NPK+FYM). Bulk soils as well as macro- and micro-aggregates were incubated for 24days at 25°C and 35°C. Cumulative SOC mineralization (Ct) in the 0–15cm soil layer of bulk soils with NPK+FYM and NPK treated plots were similar but significantly higher than unfertilized control plots. However, both Ct and Q10 values in the NPK+FYM plots were higher than NPK in the 15–30cm soil layer. In the 0–15cm soil layer, NPK+FYM plots had ∼10 and 26% greater Q10 values of macro- and microaggregates than NPK. Activation energies required for bulk soils C mineralization was ∼2 and 3 times higher in NPK+FYM and NPK+L plots, respectively, compared with unfertilized control plots in that layer. Lime along with NPK application increased the activation energy of SOC decomposition. Thus, long-term NPK+FYM and NPK+L applications have great potential for less proportional SOC decomposition than NPK or unfertilized control plots under a temperature rise in these acid soils. However, NPK+FYM management practice is recommended as it has highest SOC accumulation and can have less SOC losses under a temperature rise.

Compost effects on leaf area index and seed production enhancement in an important arid land leguminous tree Acacia tortilis subsp. Raddiana

This study aimed to investigate the effects of compost addition on leaf area index (LAI), diameter growth and enhancement of seed production and quality in Acacia tortilis established under supplementary drip irrigation. Three composted fertilizer doses (2.5 kg, 5 kg and 7.5 kg/ tree) were compared to NPK (18-18-5 at a rate of 250 gram per tree) and control unfertilized plots. Effects of compost application on leaf area index (LAI), diameter growth, relative monthly diameter increment (RMDI) were monitored during two consecutive years (2014 and 2015). Then the impacts on pods and seeds production, seed weight, seed number per kg, seed quality (NPK and protein), germination per cent and mean germination time (MGT) were determined. Addition of fertilizers produced high effects on LAI. In 2014 NPK resulted in highest LAI values in most measurements, alternatively the status was changed in 2015 where, higher doses of compost produced higher LAI values. LAI results exhibited temporal variability that was associated with the seasonal variation of the year. The results demonstrate higher RMDI and diameter growth under NPK and compost at rate of 7.5 kg/tree treatments. Pods production was higher in plots treated with higher doses of compost. However, seed/husk ratio was higher in NPK plots. There is observed association between fruit and seed production with LAI. NPK and protein contents in seeds, were also, influenced by the presence of organic fertilizers. Cumulative germination and MGT were correlated with seed weight and were higher in plots treated with compost. The results highlight the importance of organic fertilizers under dry land conditions that produced higher LAI and growth which enhanced seed production and quality.

Species-rich grassland can persist under nitrogen-rich but phosphorus-limited conditions

AimDeposition of nitrogen is assumed to cause loss of botanical diversity, probably through increased production and exclusion of less competitive species. However, if production is (co-)limited by phosphorus, acceleration of the phosphorus cycle may be responsible for the diversity loss and, where that is the case, nitrogen emission reduction may turn out to be an ineffective mitigation strategy. Here we study the feasibility of this mechanism through adding potassium and phosphorus to grassland where nitrogen limitation is absent.MethodsWe made vegetation relevés in a long-term agricultural fertilisation experiment where potassium, phosphorus and nitrogen were being added to grassland on drained peat where nitrogen availability was high, even in unfertilised plots. We applied a multivariate analysis to investigate the effect of additions of K, K + P and K + P + N on the species composition.ResultsUnfertilised plots had a very low biomass production and were rich in plant species despite their high nitrogen availability. Addition of potassium led to a strongly increased production but did not result in a reduction of species numbers. Phosphorus in addition to potassium increased production still further and decreased species numbers, most notably the number of endangered species.ConclusionsEven under nitrogen rich conditions species richness may be high in grasslands where phosphorous provides a limitation to plant growth. Phosphorus limitation and phosphorus enrichment are both common in grassland, at least in north-western Europe. Part of the general decrease in species numbers that is commonly ascribed to nitrogen enrichment may therefore be due to phosphorus enrichment. If phosphorus and nitrogen are co-limiting (which is often the case) the current nitrogen emission reduction policies may be effective, but not sufficient to restore grassland diversity to its pre-industrial level.

Effects of cotton (Gossypium hirsutum L.) straw and its biochar application on NH3 volatilization and N use efficiency in a drip-irrigated cotton field

ABSTRACTReducing ammonia (NH3) volatilization is a practical way to increase nitrogen (N) fertilizer use efficiency (NUE). In this field study, soil was amended once with either cotton (Gossypium hirsutum L.) straw (6 t ha−1) or its biochar (3.7 t ha−1) unfertilized (0 kg N ha−1) or fertilized (450 kg N ha−1), and then soil inorganic N concentration and distribution, NH3 volatilization, cotton yield and NUE were measured during the next two growing seasons. In unfertilized plots, NH3 volatilization losses in the straw-amended and biochar-amended treatments were 38–40% and 42–46%, respectively, less than that in control (i.e., unamended soil) during the two growing seasons. In the fertilized plots, NH3 volatilization losses in the straw-amended and biochar-amended treatments were 30–39% and 43–54%, respectively, less than that in the control. Straw amendment increased inorganic N concentrations, cotton yield, cotton N uptake and NUE during the first cropping season after application, but not during the second. In contrast, biochar increased cotton N uptake and NUE during both the first and the second cropping seasons after application. Furthermore, the effects of biochar on cotton N uptake and NUE were greater in the second year than in the first year. These results indicate that cotton straw and cotton straw biochar can both reduce NH3 volatilization and also increase cotton yield, N uptake and NUE. In addition, the positive effects of one application of cotton straw biochar were more long-lasting than those of cotton straw.

Residual Effects of Fertilization History Increase Nitrous Oxide Emissions from Zero-N Controls: Implications for Estimating Fertilizer-Induced Emission Factors.

Agricultural N fertilization is the dominant driver of increasing atmospheric nitrous oxide (NO) concentrations over the past half-century, yet there is considerable uncertainty in estimates of NO emissions from agriculture. Such estimates are typically based on the amount of N applied and a fertilizer-induced emission factor (EF), which is calculated as the difference in emissions between a fertilized plot and a zero-N control plot divided by the amount of N applied. A fertilizer-induced EF of 1% is currently recognized by the Intergovernmental Panel on Climate Change (IPCC) based on several studies analyzing published field measurements of NO emissions. Although many zero-N control plots used in these measurements received historical N applications, the potential for a residual impact of these inputs on NO emissions has been largely ignored and remains poorly understood. To address this issue, we compared NO emissions under laboratory conditions from soils sampled within zero-N control plots that had historically received N inputs versus soils from plots that had no N inputs for 20 yr. Historical N fertilization of zero-N control plots increased initial NO emissions by roughly one order of magnitude on average relative to historically unfertilized control plots. Higher NO emissions were positively correlated with extractable N and potentially mineralizable N. This finding suggests that accounting for fertilization history may help reduce the uncertainty associated with the IPCC fertilizer-induced EF and more accurately estimate the contribution of fertilizer N to agricultural NO emissions, although further research to demonstrate this relationship in the field is needed.

Microbial communities after wood ash fertilization in a boreal drained peatland forest

Wood ash contains all the essential plant nutrients except nitrogen, and thus supports tree growth especially on peatlands where mineral nutrients often are in short supply. Here we report the effects of wood ash fertilization on the soil microbial community in a boreal drained peatland, characterized by phospholipid fatty acid (PLFA) composition, and more specifically the fungal community, characterized with PCR-DGGE fingerprinting and sequencing methods. We investigated the microbial communities in unfertilized and ash-fertilized sample plots (loose wood ash 5000 or 15 000 kg ha−1) 6 years after fertilization. Microbial function measured as heterotrophic basal respiration increased over 30% in the surface peat layer after wood ash fertilization, yet the result was statistically insignificant. The higher amount of wood ash induced a shift in the microbial community in the surface peat layer (0–10 cm) along with an increase in pH. A higher relative proportion of fungal-specific PLFA 18:2ω6 and an increased fungal:bacterial ratio indicated that fungi benefited from the higher amount of wood ash in the topmost layer. Also, the lower amount of wood ash seemed to have stimulated actinobacteria. Our results indicated that higher pH and extra nutrients due to wood ash fertilization promoted the appearance of mycorrhizal and wood-decomposing fungi directly or via increased tree growth. We suggest that wood ash as a fertilizer would be a natural and economical choice to improve the nutrient status of drained peatlands used for forestry since it maintains the positive feedback between fungi and trees.