Joann K. Whalen

Carbon and nitrogen mineralization from light- and heavy- fraction additions to soil

Mineralization of C and N from soil organic matter (SOM) can be altered when natural ecosystems are transformed for food and fiber production. We examined C and N dynamics in adjacent long-term minimally disturbed and disturbed soils from agricultural and forest sites. Light and heavy fractions (LF and HF, respectively) of SOM were collected by physical density separation using sodium polytungstate. Aerobic C and N mineralization of soil (WS), soil plus HF (S+HF) and soil plus LF (S+LF) mixtures were determined. Between 0.8% and 1.7% of C and 0.3% and 1.2% of N from WS was mineralized after 28 days. The proportion of C mineralized from HF was negligible in all sites, suggesting that the HF component of soils could be a major sink for C storage in soils. Larger proportions of N from HF were mineralized in disturbed than minimally-disturbed soils, suggesting greater protection of N in the HF of disturbed soils. The proportion of C mineralized from LF ranged from ˇ0.3% to 3.2%, and was not consistent with C mineralization dynamics from the HF component of soils. It appeared that, while the LF component of soil contained C that was chemically and, to a lesser extent, physically protected from decomposition, more C was potentially mineralizable from the LF than the HF component of the agricultural and forest soils examined. In most soils, LF additions resulted in N immobilization rather than N mineralization. Our results indicate that HF is the main source of potentially mineralizable N whereas LF is a potential sink for mineral N, regardless of land management practices, in the agricultural and forest soils we examined. 7 2000 Elsevier Science Ltd. All rights reserved.

Nitrogen Dynamics and Indices to Predict Soil Nitrogen Supply in Humid Temperate Soils

Abstract Knowledge of the nitrogen (N) available to crops during the growing season is essential for improving fertilizer-use efficiency and minimizing the adverse impacts of N losses on the environment. In humid temperate regions, soil N supply is dominated by in-season N mineralization because plant-available N (NH 4 –N and NO 3 –N) is transformed to nonlabile forms or lost from the soil–plant system during fall and winter. The microbially mediated reactions that generate the soil N supply in agroecosystems are affected by system-specific conditions, including soil properties, agricultural management (crop rotation, tillage system, organic amendments), and most importantly, climate. Potentially mineralizable N ( N 0 ) determined from long-term soil incubation is regarded as the standard measure of soil N mineralization potential and may provide a good approximation of the soil N supply. However, this method is time consuming and not practical for routine use. Several chemical methods to estimate the N mineralization potential of soils are discussed in this chapter. The major limitation of chemical methods is that they cannot simulate the microbial-mediated release of plant-available N under field conditions. Consequently, any single chemical method may not be a good predictor of soil N supply. Thus, we suggest a holistic approach to estimate soil N supply in humid temperate regions, which involves (1) the use of a combination of N indices together with weather data and (2) identification and quantification of a specific fraction (s) of organic N that is the dominant contributor (s) to N supply in a particular system.

Population dynamics of earthworm communities in corn agroecosystems receiving organic or inorganic fertilizer amendments

Abstract The dynamics of earthworm populations were investigated in continuously-cropped, conventional disk-tilled corn agroecosystems which had received annual long-term (6 years) amendments of either manure or inorganic fertilizer. Earthworm populations were sampled at approximately monthly intervals during the autumn of 1994 and spring and autumn of 1995 and 1996. The dominant earthworm species were Lumbricus terrestris L. and Aporrectodea tuberculata (Eisen), which comprised 50–60% and 8–13%, respectively, of the total annual earthworm biomass. Lumbricus rubellus (Hoffmeister) and Aporrectodea trapezoides (Dugés) were much less abundant and contributed a small fraction of total earthworm biomass. Earthworm numbers and biomass were significantly greater in manure-amended plots compared to inorganic fertilizer-treated plots during the majority of the study period. Seasonal fluctuations in earthworm numbers and biomass were attributed to changes in soil temperature and moisture, and cultivation. Unfavorable climatic conditions in the summer and autumn of 1995 caused earthworm abundance and biomass to decline significantly. Mature L. terrestris, L. rubellus and A. tuberculata were most abundant in May and June of 1995 and 1996, and cocoon production was greatest in June and July 1995 and June 1996. Recruitment of juveniles of Lumbricus spp. and Aporrectodea spp. into earthworm communities occurred primarily in the autumn. Long-term amendments of manure or inorganic fertilizer did not change the species composition of earthworm communities in these agroecosystems. The earthworm populations in both manure and inorganic fertilizer plots have declined significantly after 5 years of continuously-cropped corn.

Movement of N from decomposing earthworm tissue to soil, microbial and plant N pools

A microcosm experiment was made to determine the fate of nitrogen released from 15 N-labelled decomposing earthworms (Lumbricus terrestris) in soil in the presence or absence of ryegrass seedlings (Lolium perenne). Earthworm tissue (2.0% 15 N atom enriched) was added to each microcosm. Nitrogen movement from earthworm tissue to soil N [mineral N (NH4-N+NO3N), dissolved organic N (DON) and organic N], microbial biomass N and plant shoot N pools was determined by destructive sampling at 1, 2, 4, 8 and 16 d. Earthworm tissues decomposed rapidly, and no tissue was visible after 4 d. Initially in pots without plants, most of the N from earthworm tissue was found in the organic N pool, however, as much as 55% of the N from decomposing earthworm tissue was incorporated into microbial biomass after 2 d. Much less of the N from earthworm tissue was transformed into DON and mineral N forms after 2 d. The DON and mineral N pools contained 13‐18% and 4‐7% of the N from earthworm tissue, respectively, from d 2 to 16. By the end of the experiment, N from earthworm tissue in the microbial biomass N pool declined to 29% while the amount of N from earthworm tissue in the organic N pool increased to 49%. The increase in the organic N may have resulted from the production of new organic compounds such as microbial by-products. In pots with plants, N from earthworm tissue was rapidly incorporated into microbial biomass, and by d 2, the microbial biomass N pool contained 40% of the N from earthworm tissue. Mineral N, DON and microbial biomass N concentrations were lower in pots with ryegrass seedlings compared to pots without plants, and after d 2 declined to almost undetectable amounts because of rapid plant uptake. Between 42‐52% of the N from earthworm tissue was found in the organic N pool from d 1 to 8, and then declined to 19% by d 16. After 16 d, over 70% of the N added as earthworm tissue was incorporated into plant shoot biomass. Our results demonstrate that the movement of N from dead earthworm tissue into microbial biomass was extremely rapid, and in pots without plants, much of this N was transformed into organic N forms, while in pots with ryegrass, most of the N from earthworm tissue accumulated in ryegrass shoots. # 1999 Elsevier Science Ltd. All rights reserved.

Earthworm Sublethal Responses to Titanium Dioxide Nanomaterial in Soil Detected by 1H NMR Metabolomics

¹H NMR-based metabolomics was used to examine the response of Eisenia fetida earthworms raised from juveniles for 20-23 weeks in soil spiked with either 20 or 200 mg/kg of a commercially available uncoated titanium dioxide (TiO(2)) nanomaterial (nominal diameter of 5 nm). To distinguish responses specific to particle size, soil treatments spiked with a micrometer-sized TiO(2) material (nominal diameter, <45 μm) at the same concentrations (20 and 200 mg/kg) were also included in addition to an unspiked control soil. Multivariate statistical analysis of the (1)H NMR spectra for aqueous extracts of E. fetida tissue suggested that earthworms exhibited significant changes in their metabolic profile following TiO(2) exposure for both particle sizes. The observed earthworm metabolic changes appeared to be consistent with oxidative stress, a proposed mechanism of toxicity for nanosized TiO(2). In contrast, a prior study had observed no impairment of E. fetida survival, reproduction, or growth following exposure to the same TiO(2) spiked soils. This suggests that (1)H NMR-based metabolomics provides a more sensitive measure of earthworm response to TiO(2) materials in soil and that further targeted assays to detect specific cellular or molecular level damage to earthworms caused by chronic exposure to TiO(2) are warranted.

Earthworm services for cropping systems. A review

Intensive agriculture is often criticized for negative impacts on environment and human health. This issue may be solved by a better management of organisms living in crop fields. Here, we review the benefits of earthworms for crops, and we present techniques to increase earthworm abundance. The major points are the following: (1) Earthworms usually improve soil structural stability and soil porosity and reduce runoff. (2) Earthworms modify soil organic matter (SOM) and nutrient cycling. Specifically, earthworms stabilize SOM fractions within their casts, and they also increase the mineralization of organic matter in the short term by altering physical protection within aggregates and enhancing microbial activity. (3) The positive correlation between earthworm abundance and crop production is not systematic, and contrasting effects on yields have been observed. Earthworms induce the production of hormone-like substances that improve plant growth and health. (4) Direct drilling increases earthworm abundance and species diversity, but the beneficial effect of reduced tillage depends upon the species present and tillage intensity. (5) Organic amendments enhance earthworm abundance. (6) Earthworms feeding at soil surface are the most exposed to pesticides and other agrochemicals. Finally, we discuss how to combine management practices, including inoculation, to increase the earthworm services. We conclude that using earthworm services in cropping systems has potential to boost agricultural sustainability.

Reproductive and behavioral responses of earthworms exposed to nano‐sized titanium dioxide in soil

Nanometer-sized titanium dioxide (nano-TiO(2) ) is found in a number of commercial products; however, its effects on soil biota are largely unknown. In the present study, earthworms (Eisenia andrei and Eisenia fetida) were exposed to three types of commercially available, uncoated TiO(2) nanomaterials with nominal diameters of 5, 10, and 21 nm. Nanomaterials were characterized for particle size, agglomeration, surface charge, chemical composition, and purity. Standard lethality, reproduction, and avoidance tests, as well as a juvenile growth test, were conducted in artificial soil or field soil amended with nano-TiO(2) by two methods, liquid dispersion and dry powder mixing. All studies included a micrometer-sized TiO(2) control. Exposure to field and artificial soil containing between 200 and 10,000 mg nano-TiO(2) per kilogram of dry soil (mg/kg) had no significant effect (p > 0.05) on juvenile survival and growth, adult earthworm survival, cocoon production, cocoon viability, or total number of juveniles hatched from these cocoons. However, earthworms avoided artificial soils amended with nano-TiO(2) . The lowest concentration at which avoidance was observed was between 1,000 and 5,000 mg nano-TiO(2) per kilogram of soil, depending on the TiO(2) nanomaterial applied. Furthermore, earthworms differentiated between soils amended with 10,000 mg/kg nano-TiO(2) and micrometer-sized TiO(2) . A positive relationship between earthworm avoidance and TiO(2) specific surface area was observed, but the relationship between avoidance and primary particle size was not determined because of the agglomeration and aggregation of nano-TiO(2) materials. Biological mechanisms that may explain earthworm avoidance of nano-TiO(2) are discussed. Results of the present study indicate that earthworms can detect nano-TiO(2) in soil, although exposure has no apparent effect on survival or standard reproductive parameters.

Quantification of nitrogen excretion rates for three lumbricid earthworms using 15N

Abstract Nitrogen excretion rates of 15N-labeled earthworms and contributions of 15N excretion products to organic (dissolved organic N) and inorganic (NH4-N, NO3-N) soil N pools were determined at 10  °C and 18  °C under laboratory conditions. Juvenile and adult Lumbricus terrestris L., pre-clitellate and adult Aporrectodea tuberculata (Eisen), and adult Lumbricus rubellus (Hoffmeister) were labeled with 15N by providing earthworms with 15N-labeled organic substrates for 5–6 weeks. The quantity of 15N excreted in unlabeled soil was measured after 48 h, and daily N excretion rates were calculated. N excretion rates ranged from 274.4 to 744 μg N g–1 earthworm fresh weight day–1, with a daily turnover of 0.3–0.9% of earthworm tissue N. The N excretion rates of juvenile L. terrestris were significantly lower than adult L. terrestris, and there was no difference in the N excretion rates of pre-clitellate and adult A. tuberculata. Extractable N pools, particularly NH4-N, were greater in soils incubated with earthworms for 48 h than soils incubated without earthworms. Between 13 and 40% of excreted 15N was found in the 15N-mineral N (NH4-N+NO3-N) pool, and 13–23% was in the 15N-DON pool. Other fates of excreted 15N may have been incorporation in microbial biomass, chemical or physical protection in non-extractable N forms, or gaseous N losses. Earthworm excretion rates were combined with earthworm biomass measurements to estimate N flux from earthworm populations through excretion. Annual earthworm excretion was estimated at 41.5 kg N ha–1 in an inorganically-fertilized corn agroecosystem, and was equivalent to 22% of crop N uptake. Our results suggest that the earthworms could contribute significantly to N cycling in corn agroecosystems through excretion processes.

Chapter three - Agricultural Practices in Oil Palm Plantations and Their Impact on Hydrological Changes, Nutrient Fluxes and Water Quality in Indonesia: A Review

Rapid expansion of oil palm (Elaeis guineensis Jacq.) cultivation in Southeast Asia raises environmental concerns about deforestation and greenhouse gas emissions. However, less attention was paid to the possible perturbation of hydrological functions and water quality degradation. This work aimed to review (i) the agricultural practices commonly used in oil palm plantations, which potentially impact hydrological processes and water quality and (ii) the hydrological changes and associated nutrient fluxes from plantations. Although many experimental trials provide clear recommendations for water and fertilizer management, we found that few studies investigated the agricultural practices actually followed by planters. Our review of hydrological studies in oil palm plantations showed that the main hydrological changes occurred during the first years after land clearing and seemed to dissipate with plant growth, as low nutrient losses were generally reported from plantations. However, most of those studies were carried out at the plot scale and often focus on one hydrological process at a single plantation age. So, there is insufficient information to evaluate the spatiotemporal fluctuations in nutrient losses throughout the entire lifespan of a plantation. Furthermore, few studies provided an integrated view at the watershed scale of the agricultural practices and hydrological processes that contribute to nutrient losses from oil palm plantations and the consequences for surface and groundwater quality. Future research efforts need to understand and assess the potential of oil palm plantations to change hydrological functions and related nutrient fluxes, considering agricultural practices and assessing water quality at the watershed scale.

Linking spatio-temporal dynamics of earthworm populations to nutrient cycling in temperate agricultural and forest ecosystems

Numerous laboratory and small plot-scale studies have highlighted the importance of earthworm populations in decomposition and nutrient cycling. However, the simple scaling up of such results to explain conditions on a large field scale, across agricultural landscapes under varied management scenarios, or across landscapes made up of different types of ecosystems (agricultural, grassland, forest), is very much constrained by a lack of information about the spatiotemporal distribution of earthworm populations. This study documents the spatiotemporal variation in earthworm populations in temperate ecosystems. A mixed deciduous forest, grass-dominated hayfield and corn agroecosystem were each fitted with a single 50 m x 50 m sampling grid, consisting of twenty-five 10 m x 10 m cells. Earthworms were collected at distinct single georeferenced locations in each of the 25 cells. Locations varied according to the sampling date (May, July or September). The earthworms collected by hand-sorting and formalin extraction, were first separated by species, then counted and weighed. The soil characteristics (temperature and moisture content, extractable nutrients, organic matter, pH) were also assessed for each time and location. Geostatistical and correlation analyses served to generate spatial maps of earthworm populations and to assess which soil factors most closely paralleled the numerical distribution of earthworms. This provided some insight into small-scale heterogeneity in earthworm populations, possibly allowing for the future extrapolation of laboratory and controlled field study results to larger scales, and in turn a more accurate estimation of the role of earthworms in nutrient cycling at the ecosystem and landscape levels.