Increase In Total Soil Research Articles

Effects of free atmospheric CO<sub>2</sub> enrichment (FACE), N fertilization and poplar genotype on the physical protection of carbon in the mineral soil of a polar plantation after five years

Abstract. Free air CO2 enrichment (FACE) experiments in aggrading forests and plantations have demonstrated significant increases in net primary production (NPP) and C storage in forest vegetation. The extra C uptake may also be stored in forest floor litter and in forest soil. After five years of FACE treatment at the EuroFACE short rotation poplar plantation, the increase of total soil C% was larger under elevated than under ambient CO2. However, the fate of this additional C allocated belowground remains unclear. The stability of soil organic matter is controlled by the chemical structure of the organic matter and the formation of micro-aggregates (within macro-aggregates) in which organic matter is stabilized and protected. FACE and N-fertilization treatment did not affect the micro- and macro-aggregate weight, C or N fractions obtained by wet sieving. However, Populus euramericana increased the small macro-aggregate and free micro-aggregate weight and C fractions. The obtained macro-aggregates were broken up in order to isolate recently formed micro-aggregates within macro-aggregates (iM-micro-aggregates). FACE increased the iM-micro-aggregate weight and C fractions, although not significantly. This study reveals that FACE did not affect the formation of aggregates. We did, however, observe a trend of increased stabilization and protection of soil C in micro-aggregates formed within macro-aggregates under FACE. Moreover, the largest effect on aggregate formation was due to differences in species, i.e. poplar genotype. P. euramericana increased the formation of free micro-aggregates which means that more newly incorporated soil C was stabilized and protected. The choice of species in a plantation, or the effect of global change on species diversity, may therefore affect the stabilization and protection of C in soils.

Modeled carbon sequestration variation in a linked erosion–deposition system

Unraveling the consequences of hydrologic transport on carbon (C) storage will help identify feedbacks between land management alternatives, climate change, and soil-vegetation-atmospheric-transfers (SVATs) of C. There is a need for theoretically driven models of erosion and deposition that includes transport induced mineralization to better understand the controls on SVATs of C. Here we present a model developed using a systems-dynamic approach that coupled C-SVATs at a 2-day resolution with a discrete event erosion–deposition model occurring with a prescribed return interval. Five possible mass-balance transformations of C occurring between the two patches were explicitly modeled: net primary production (NPP), decomposition, erosion, transport induced mineralization, and deposition. The net C-SVAT, NPP minus decomposition, exhibited three stable points of no net C flux. Starting with arbitrary initial C pool in each patch above the bifurcation point, the model approached a quasi-steady state, which included both the short-term and longer term consequences of erosion; in the baseline simulation 5080 g C m −2 was stored prior to erosion and 100 years of low intensity erosion 4840 g C m −2 SOC remained. Low intensity erosion also generated spatial heterogeneity; from an initial homogeneous distribution to 40% of the C stored in the eroded patch and 60% of the C stored in the deposition patch. Erosion reduction resulted in a corresponding increase in total soil C content that was positively related to the magnitude of erosion reduction. In conjunction with providing a modeling framework for reducing the uncertainty in C-SVAT, this model is a prototype of a growing theory of ecosystem processes within spatially explicit landscapes, a meta-ecosystem model.

Soil carbon pools and fluxes after land conversion in a semiarid shrub-steppe ecosystem

Worldwide soil carbon (C) losses associated with agricultural expansion and intensification have contributed significantly to increased atmospheric CO2. Soil distur- bances resulting from land use changes were shown to modify the turnover of C and the formation of soil organic matter. A native semiarid shrub-steppe ecosystem recently converted into an irrigated agricultural development in the Columbia Basin of Washington State was evaluated for several abiotic indicators that might signal changes in an ecosystem during the initial stages of conversion and disturbance. Soil samples were collected in March of 2003 and 2004 from nine sites that included native shrub- steppe and agricultural fields converted in 2001 and 2002. Disturbance from conversion to irrigated crop production influenced total organic C and nitrogen (N) storage, C and N mineralization, and C turnover. Cultivated fields had greater concentrations of total organic C and N and higher cumulative C and N mineralization than native sites after 3 years of cultivation. Soil organic C was divided into three pools: an active pool (Ca) consisting of labile C (simple sugars, organic acids, the microbial biomass, and metabolic compounds of incorporated plant residues) with a mean residence time of days, an intermediate or slow pool (Cs) consisting of structural plant residues and physically stabilized C, and a resistant fraction (Cr) consisting of lignin and chemically stabilized C. Extended laboratory incubations of soil with measurements of CO2 were used to differentiate the size and turnover of the Ca and Cs functional C pools. The active pools were determined to be 4.5 and 6.5% and slow pools averaged 44 and 47% of the total C in native and cultivated fields, respectively. Cultiva- tion, crop residue incorporation, and dairy manure compost amendments contributed to the increase in total soil C.

Carbon and Nitrogen Pools in a Tallgrass Prairie Soil under Elevated Carbon Dioxide

Soil is a potential C sink and could offset rising atmospheric CO2 The capacity of soils to store and sequester C will depend on the rate of C inputs from plant productivity relative to C exports controlled by microbial decomposition. Our objective was to measure pools of soil C and N to assess the potential for C accrual and changes to N stocks as influenced by elevated atmospheric CO2 Treatments (three replications, randomized complete block design) were ambient CO2—no chamber (NC), ambient CO2—chamber (AC), and two times ambient CO2—chamber (EC). Long‐term (290 d) incubations (35°C) were conducted to assess changes in the slow soil fractions of potentially mineralizable C (PMC) and potentially mineralizable N (PMN). Potentially mineralizable C was enhanced (P < 0.1) by 19 and 24% in EC relative to AC and NC soil at the 0‐ to 5‐ and 5‐ to 15‐cm depths, respectively. Potentially mineralizable N was significantly greater by 14% at the 0‐ to 5‐cm depth in EC relative to AC, but decreased by 12% in EC relative to NC (P < 0.1). Measurements of PMC indicate that increases in total soil C under elevated CO2 in a previous study were a consequence of accrual into the slow pool. Relatively large amounts of new C deposited as a result of elevated CO2 (Cnew) remained in the soil after the 290‐d incubation. In contrast to accumulation of C into the slow fraction, Cnew was integrated into a passive fraction of soil organic matter (SOM). Accumulation of N was also detected in the whole soil, which cannot be explained by current estimates of ecosystem N flux.

Soil 13C–15N dynamics in an N2‐fixing clover system under long‐term exposure to elevated atmospheric CO2

AbstractReduced soil N availability under elevated CO2 may limit the plant's capacity to increase photosynthesis and thus the potential for increased soil C input. Plant productivity and soil C input should be less constrained by available soil N in an N2‐fixing system. We studied the effects of Trifolium repens (an N2‐fixing legume) and Lolium perenne on soil N and C sequestration in response to 9 years of elevated CO2 under FACE conditions. 15N‐labeled fertilizer was applied at a rate of 140 and 560 kg N ha−1 yr−1 and the CO2 concentration was increased to 60 Pa pCO2 using 13C‐depleted CO2. The total soil C content was unaffected by elevated CO2, species and rate of 15N fertilization. However, under elevated CO2, the total amount of newly sequestered soil C was significantly higher under T. repens than under L. perenne. The fraction of fertilizer‐N (fN) of the total soil N pool was significantly lower under T. repens than under L. perenne. The rate of N fertilization, but not elevated CO2, had a significant effect on fN values of the total soil N pool. The fractions of newly sequestered C (fC) differed strongly among intra‐aggregate soil organic matter fractions, but were unaffected by plant species and the rate of N fertilization. Under elevated CO2, the ratio of fertilizer‐N per unit of new C decreased under T. repens compared with L. perenne. The L. perenne system sequestered more 15N fertilizer than T. repens: 179 vs. 101 kg N ha−1 for the low rate of N fertilization and 393 vs. 319 kg N ha−1 for the high N‐fertilization rate. As the loss of fertilizer‐15N contributed to the 15N‐isotope dilution under T. repens, the input of fixed N into the soil could not be estimated. Although N2 fixation was an important source of N in the T. repens system, there was no significant increase in total soil C compared with a non‐N2‐fixing L. perenne system. This suggests that N2 fixation and the availability of N are not the main factors controlling soil C sequestration in a T. repens system.

Bermudagrass management in the Southern Piedmont U.S. IV. Soil surface nitrogen pools.

The fate of nitrogen (N) applied in forage-based agricultural systems is important for understanding the long-term production and environmental impacts of a particular management strategy. We evaluated the factorial combination of three types of N fertilization (inorganic, crimson clover [Trifolium incarnatum L.] cover crop plus inorganic, and chicken [Gallus gallus] broiler litter pressure and four types of harvest strategy (unharvested forage, low and high cattle [Bos Taurus] grazing pressure, and monthly haying in summer) on surface residue and soil N pools during the first 5 years of ‘Coastal’ bermudagrass (Cynodon dactylon [L.] Pers.) management. The type of N fertilization used resulted in small changes in soil N pools, except at a depth of 0 to 2 cm, where total soil N was sequestered at a rate 0.2 g ‧ kg‧ year1 greater with inorganic fertilization than with other fertilization strategies. We could account for more of the applied N under grazed systems (76–82%) than under ungrazed systems (35–71%). As a percentage of applied N, 32 and 48% were sequestered as total soil N at a depth of 0 to 6 cm when averaged across fertilization strategies under low and high grazing pressures, respectively, which was equivalent to 6.8 and 10.3 g ‧ m ‧ year. Sequestration rates of total soil N under the unharvested-forage and haying strategies were negligible. Most of the increase in total soil N was at a depth of 0 to 2 cm and was due to changes in the particulate organic N (PON) pool. The greater cycling of applied N into the soil organic N pool with grazed compared with ungrazed systems suggests an increase in the long-term fertility of soil.

Distribution and forms of P under cultivator- and zero-tillage for continuous- and fallow-wheat cropping systems in the semi-arid Canadian prairies

Conservation tillage may affect the dynamics of nutrient transformations in the soil. We assessed the effect of fallow-wheat, and continuous wheat under zero-tillage and cultivator-tillage management on phosphorus concentration in the grain (GPC), phosphorus uptake in the grain, NaHCO 3 extractable-P (Olsen-P) and on forms and distribution of P in the surface 10 cm of the soil for a 12-year tillage field experiment established on an Orthic Brown Chernozemic soil (Aridic Haploboroll) in southwestern Saskatchewan, Canada. Grain yield was the main factor affecting GPC, with the lower-yielding continuous-wheat system having the highest GPC, most likely resulting from luxury uptake of P. Phosphorus taken in the grain, however, was directly proportional to grain yield. Olsen-P in the soil was highly variable from year to year, and was not affected by tillage or rotation. From 1982 to 1989, when P removed in the grain was less than P applied as fertilizer, Olsen-P in spring samples increased, on average, by 0.9 mg kg −1 year −1 in the fallow-wheat and by 1.4 mg kg −1 year −1 in the continuous-wheat cropping systems. From 1990 to 1994, when grain yields increased due to more favourable moisture conditions, crop removal of P exceeded P fertilization, and Olsen-P concentration remained relatively stable. Converting the original cultivator tilled fallow-wheat system to zero-tilled continuous wheat produced a significant increase in total soil P as a result of increased accumulation of labile and moderately labile forms of P in the surface 6 cm of the soil, especially in organic forms. When either zero-tillage or continuous-wheat were adopted by themselves, there were no changes in the amounts of P in the different pools. The proportion of organic P in the labile and moderately labile pools in the surface 6 cm of soil, however, increased significantly with respect to the cultivator tilled fallow-wheat control. This reflected increased levels of crop residues returned to the soil in the continuous-wheat cropping system and reduced rates of residue decomposition in the zero-tillage system. The increase in labile forms of P near the surface in zero-tilled soils may have substantial impact on soil sampling for prediction of P fertilizer requirements, and on surface water quality in reduced tillage systems.

The effects of long-term applications of inorganic nitrogen fertilizer on soil nitrogen in the Broadbalk Wheat Experiment

SUMMARYThe Broadbalk Wheat Experiment at Rothamsted (UK) includes plots given the same annual applications of inorganic nitrogen (N) fertilizer each year since 1852 (48, 96 and 144 kg N/ha, termed N1 N2 and N3 respectively). These very long-term N treatments have increased total soil N content, relative to the plot never receiving fertilizer N (N0), due to the greater return of organic N to the soil in roots, root exudates, stubble, etc (the straw is not incorporated). The application of 144 kg N/ha for 135 years has increased total soil N content by 21%, or 570 kg/ha (0–23 cm). Other plots given smaller applications of N for the same time show smaller increases; these differences were established within 30 years. Increases in total soil N content have been detected after 20 years in the plot given 192 kg N/ha since 1968 (N4).There was a proportionally greater increase in N mineralization. Crop uptake of mineralized N was typically 12–30 kg N/ha greater from the N3 and N4 treatments than the uptake of c. 30 kg N/ha from the N0 treatment. Results from laboratory incubations show the importance of recently added residues (roots, stubble, etc) on N mineralization. In short-term (2–3 week) incubations, with soil sampled at harvest, N mineralization was up to 60% greater from the N3 treatment than from N0. In long-term incubations, or in soil without recently added residues, differences between long-term fertilizer treatments were much less marked. Inputs of organic N to the soil from weeds (principally Equisetum arvense L.) to the N0–N2 plots over the last few years may have partially obscured any underlying differences in mineralization.The long-term fertilizer treatments appeared to have had no effect on soil microbial biomass N or carbon (C) content, but have increased the specific mineralization rate of the biomass (defined as N mineralized per unit of biomass).Greater N mineralization will also increase losses of N from the system, via leaching and gaseous emissions. In December 1988 the N3 and N4 plots contained respectively 14 and 23 kg/ha more inorganic N in the profile (0–100 cm) than the N0 plot, due to greater N mineralization. These small differences are important as it only requires 23 kg N/ha to be leached from Broadbalk to increase the nitrate concentration of percolating water above the 1980 EC Drinking Water Quality Directive limit of 11·3mgN/l.The use of fertilizer N has increased N mineralization due to the build-up of soil organic N. In addition, much of the organic N in Broadbalk topsoil is now derived from fertilizer N. A computer model of N mineralization on Broadbalk estimated that after applying 144 kg N/ha for 140 years, up to half of the N mineralized each year was originally derived from fertilizer N.In the short-term, the amount of fertilizer N applied usually has little direct effect on losses of N over winter. In most years little fertilizer-derived N remains in Broadbalk soil in inorganic form at harvest from applications of up to 192 kg N/ha. However, in two very dry years (1989 and 1990) large inorganic N residues remained at harvest where 144 and 192 kg N/ha had been applied, even though the crop continued to respond to fertilizer N, up to at least 240 kg N/ha.

Changes in soil chemistry associated with changes in soil-pH in Victorian pastures

Relationships between changes in soil pH and changes in other soil chemical properties were examined using data from a survey of 107 pasture sites from across Victoria. At each site, soil samples (0-5, 5-10, 10-15 and 15-20 cm depths) were taken from the pasture and an adjacent undisturbed (reference) area for chemical analysis. Changes in soil chemical properties were inferred from differences between pasture and reference soils. Increases in extractable Al and extractable Mn and decreases in the sum of exchangeable cations were associated with decreases in pH. Changes in soil organic C, total soil N and total soil P were not associated with changes in pH but were related to pasture composition at each site. Increases in total soil P and exchangeable Ca, and decreases in exchangeable Mg were partly attributed to the application of superphosphate. Decreases in electrical conductivity are discussed in relation to vegetation and salinization.

Cadmium status of soils, plants, and grazing animals in New Zealand

Abstract The accumulation of cadmium (Cd), a biotoxic heavy metal, in the food chain is undesirable. A national survey of soils and plants and random testing of kidneys from grazing animals slaughtered for export was conducted to assess Cd accumulation in New Zealand (NZ) pastoral agriculture. Average total Cd content of pastoral soils (0–7.5 cm) was 0.44 (Xg Cd/g compared to 0.20 |xg Cd/g for “native” (non‐agricultural) soils. Total soil Cd was highly correlated to total soil P. An increase in total soil P is a reflection of fertiliser history thus phosphatic fertiliser use is implicated in Cd accumulation in pastoral soils. The elevated pastoral soil Cd levels were not clearly reflected in grass or legume species but were displayed in weed species viz, 0.28 ug Cd/g c.f. 0.14 μg Cd/g for pastoral and native sites respectively. Over the period 1988–91, 22–28% of sheep and 14–20% of cattle kidneys sampled exceeded the NZ maximum residue level of 1 μg Cd/g. Kidney Cd content was highly age‐related. Cadmium was also present in feral deer and feral sheep kidneys showing that Cd occurs naturally in the environment.

The nitrogen cycle in the Broadbalk Wheat Experiment: recovery and losses of 15N-labelled fertilizer applied in spring and inputs of nitrogen from the atmosphere

SUMMARY15N-labelled nitrogen fertilizer (containing equal quantities of ammonium-N and nitrate-N) was applied in 4 consecutive years (1980–3) to different microplots located within the Broadbalk Wheat Experiment at Rothamsted, an experiment which has carried winter wheat continuously since 1843. Plots receiving 48, 96, 144 and 192 kg N/ha every year were given labelled fertilizer in mid-April at (nominally) these rates.Grain yields ranged from 1–2 t/ha on plots given no N fertilizer since 1843 to a maximum of 7·3 t/ha with 196 kg N/ha. On plots given adequate P and K fertilizer, between 51 and 68% of the labelled N was recovered in the above-ground crop; only about 40% was recovered where P deficiency limited crop growth. In 1981 fertilizerderived N retained in soil (0–70 cm) at harvest increased from 16 kg/ha, where 48 kg/ha was applied, to 38 kg/ha, where 192 kg/ha was applied. More than 80% of this retained N was in the plough layer (0–23 cm).Overall recovery of fertilizer N in crop plus soil ranged from 70 % to more than 90 % over the 4 years of the experiments. Losses of N were larger in years when spring rainfall was above average and when soil moisture deficits shortly after application were small.Crop uptake of unlabelled N derived from soil increased from 28 kg N/ha on the plot given no fertilizer N to 67 kg N/ha on the plot given 144 kg N/ha. The extra uptake of unlabelled N was mainly, if not entirely, due to greater mineralization of soil N in the plots that had been given N fertilizer for many years. Presumably fertilizer N increased the annual return of crop residues, which in turn led to an accumulation of mineralizable organic N, although there was only a small increase in total soil N content.Wheat given NH4-N grew less well and took up less N than wheat given N08-N in the relatively dry spring of 1980; there was little difference between the two forms of N in the wetter spring of 1981. In both years more fertilizer N was retained in the soil at harvest when fertilizer was applied as NH4-N than as N03-N.The N content of the soil in several plots of the experiment has been constant for many years, so that the annual removal of N is balanced by the annual input. A nitrogen balance for the plot given 144 kg fertilizer N/ha showed an average annual input of non-fertilizer N of at least 48 kg/ha, of which N in rain and seed accounts for about 14 kg/ha. The remainder may come from biological fixation of atmospheric N2 by blue-green algae, or from dry deposition of oxides of nitrogen and/or NH3 onto crop and soil. The overall annual loss of N from the crop–soil system on this particular plot was 54 kg N/ha per year, 28% of the total annual input from fertilizer and nonfertilizer N.