Nutrient Return Research Articles

The rapid return of marine-derived nutrients to a freshwater food web following dam removal

Dam removal is increasingly being recognized as a viable river restoration action. Although the main beneficiaries of restored connectivity are often migratory fish populations, little is known regarding recovery of other parts of the freshwater food web, particularly terrestrial components. We measured stable isotopes in key components to the freshwater food web: salmon, freshwater macroinvertebrates and a river specialist bird, American dipper (Cinclus mexicanus), before and after removal of the Elwha Dam, WA, USA. Less than a year after dam removal, salmon returned to the system and released marine-derived nutrients (MDN). In that same year we documented an increase in stable-nitrogen and carbon isotope ratios in American dippers. These results indicate that MDN from anadromous fish, an important nutrient subsidy that crosses the aquatic–terrestrial boundary, can return rapidly to food webs after dams are removed which is an important component of ecosystem recovery.

Litterfall, litter decomposition and associated nutrient fluxes in Pinus halepensis: influence of tree removal intensity in a Mediterranean forest

Our knowledge about the influence of silvicultural treatments on nutrient cycling processes in Mediterranean forests is still limited. Four levels of tree removal were compared in an Aleppo pine forest in eastern Spain to determine the effects on litterfall, litter decomposition and the associated nutrient fluxes after 12 years. Removal treatments included clearfelling, two shelterwood intensities (60 and 75 % of basal area removed) and untreated controls. Twelve years later, the basal area removed still explained 60 % of litterfall mass variance and 60 % of C, 52 % of N, 45 % of P, 17 % of K, 47 % of Ca and 60 % of Mg return variances. Litter decomposed somewhat more slowly in clearfellings compared to controls (p = 0.049), accumulated more Ca and released less K compared to the other three treatments. This was explained by contamination with mineral particles due to the poorly developed O horizon in clearfellings. We conclude that the management practices reduced the nutrient return via litterfall, but the nutrient release through decomposition seems poorly sensitive to canopy disturbance. In order to accurately quantify the harvesting impacts on nutrient cycling in this Mediterranean forest system, it is necessary to measure the litterfall of the understory layer.

Litterfall and nutrient return along a disturbance gradient in a tropical montane forest

Litterfall plays an important role in nutrient cycling and maintenance of soil fertility in terrestrial ecosystems. Annual and seasonal variation in litterfall have been investigated in various habitats, however, seasonality in nutrient supply is less well documented. We studied litterfall over two years and seasonal litter nutrient input over one year across a tropical disturbance gradient from mature forest to monoculture tea plantation. Total litter production in the mature forests and regenerating forests was not significantly different. However, tea plantations had significantly lower litter production. Total litterfall in forest habitats showed a clear seasonal pattern with a peak during the dry season (Mar.–May), as has been reported for other tropical seasonal forests. Contrary to expectations, there was no significant difference in litter nutrient concentrations across the disturbance gradient, although there was a substantial change in plant species composition. Litter nutrient concentrations also did not vary significantly across seasons, again contrary to our expectations. Thus, nutrient input was driven solely by the seasonal litterfall pattern. Our results suggest that at a landscape scale turnover in species composition linked to anthropogenic disturbance may not always lead to changes in litter quality, presumably because a similar spectra of leaf types may exist across communities. Seasonal litterfall patterns, which have been more commonly studied, may prove a reasonable proxy for nutrient input in forests.

Nutrient distribution indicated whole-tree harvesting as a possible factor restricting the sustainable productivity of a poplar plantation system in China.

We evaluated the biomass and contents of five major macronutrients (N, P, K, Ca and Mg) in 10-year-old poplar trees (Populus deltoids Bartr. cv. “Lux”), and determined their nutrient use efficiencies (NUEs) at Zhoushan Forestry Farm (32°20′ N, 119°40′ E), Jiangsu province, in eastern China. The above- and below-ground biomass of poplar trees was 161.7 t ha-1, of which 53.3% was stemwood. The nutrient contents in the aboveground part were as follows: 415.1 kg N ha-1, 29.7 kg P ha-1, 352.0 kg K ha-1, 1083.0 kg Ca ha-1, and 89.8 kg Mg ha-1. The highest nutrient contents were in stembark, followed by branches, roots, stemwood, and foliage. The NUEs of the aboveground parts of poplar for N, P, K, Ca and Mg were 0.313, 4.377, 0.369, 0.120, 1.448 t dry biomass kg-1 nutrient, respectively, while those of stemwood were 1.294, 33.154, 1.253, 0.667, and 3.328 t dry biomass kg-1, respectively. The cycling coefficients, defined as the percentage of annual nutrient return in annual nutrient uptake, of N, P, K, Ca and Mg for the aboveground part were 87, 95, 69, 92, and 84%, respectively. Based on the NUE and nutrient cycling characteristics, shifting from whole-tree harvesting to stemwood-only harvesting and appropriately extending the harvest rotation could prevent site deterioration and support sustainable productivity of poplar plantation systems.

Tree patch distribution drives spatial heterogeneity of soil traits in cork oak woodlands

Spatial heterogeneity of soil resources is linked to tree patch distribution in Mediterranean cork oak woodlands. Tree patch distribution modifies soil traits by varying litterfall inputs due to different tree covers. The spatial heterogeneity of soil resources affects the structure and functioning of the different plant communities on ecosystems. In Mediterranean oak woodlands, the scattered trees play a key role in this spatial heterogeneity and might strongly influence ecosystem functioning and its productivity. To assess the influence of the spatial pattern of trees and litter nutrient content on the spatial heterogeneity of soil properties. We used a combination of geostatistical techniques and a linear mixed model to evaluate the spatial heterogeneity of soil and the seasonal and spatial variability of litter nutrient content, respectively. Soil parameters showed a high spatial heterogeneity. Tree cover was positively related with soil pH, and the organic matter, N, K, and Ca soil content. The return of nutrients to the soil via leaf fall had a marked seasonality and a high spatial variability, but this spatial variability had no effect on the spatial pattern of soil resources. The spatial heterogeneity of soil in cork oak woodlands is mainly driven by tree patches distribution. The importance of the spatial heterogeneity of soil resources and the spatial pattern of trees on the functioning of the dehesa ecosystem makes it necessary to include them in plant nutrition studies and modeling approaches in these ecosystems.

Phosphate addition enhanced soil inorganic nutrients to a large extent in three tropical forests.

Elevated nitrogen (N) deposition may constrain soil phosphorus (P) and base cation availability in tropical forests, for which limited evidence have yet been available. In this study, we reported responses of soil inorganic nutrients to full factorial N and P treatments in three tropical forests different in initial soil N status (N-saturated old-growth forest and two less-N-rich younger forests). Responses of microbial biomass, annual litterfall production and nutrient input were also monitored. Results showed that N treatments decreased soil inorganic nutrients (except N) in all three forests, but the underlying mechanisms varied depending on forests: through inhibition on litter decomposition in the old-growth forest and through Al3+ replacement of Ca2+ in the two younger forests. In contrast, besides great elevation in soil available P, P treatments induced 60%, 50%, 26% increases in sum of exchangeable (K++Ca2++Mg2+) in the old-growth and the two younger forests, respectively. These positive effects of P were closely related to P-stimulated microbial biomass and litter nutrient input, implying possible stimulation of nutrient return. Our results suggest that N deposition may result in decreases in soil inorganic nutrients (except N) and that P addition can enhance soil inorganic nutrients to support ecosystem processes in these tropical forests.

Litterfall production and nutrient return in different-aged Chinese fir (Cunninghamia lanceolata) plantations in South China

The amounts of litter produced and nutrients returned play a fundamental role in the productivity and biogeochemical and nutrient cycling of forest ecosystems. We monitored annual litterfall production, nutrient return, and monthly dynamics over a one-year period in Chinese fir plantations aged 10, 22, and 34 years. Our objective was to quantify litterfall and nutrient return over a complete harvest rotation of Chinese fir. Annual litterfall production increased with stand age and was recorded as (3,294.6 ± 360.4), (3,733.9 ± 211.2), and (4,876.1 ± 212.8) kg ha−1 a−1 in stands aged 10, 22 and 34 years, respectively. Total litter production was significantly greater in the stand aged 34 years than in the stand aged 10 years (p N (39.32–62.04 kg ha−1 a−1) > K (15.95–22.44 kg ha−1 a−1) > P (1.30–1.63 kg ha−1 a−1). C, N, K and P input to soil was significantly lower in the 10-year-old stand in comparison to the 22- and 34-year-old stands (p < 0.05). Litterfall production and nutrient return (C, N and K) followed similar patterns, and C and N input to soil was significantly related to litterfall production (needle, branch and total litterfall). C, N, P and K input to soil and total litterfall production were mainly driven by needle litterfall.

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The aim of this study was to evaluate the contribution of pure stands of Eucalyptus camaldulensis and Acacia mangium for litter deposition and nutrient return in a pit of clay extraction in northern Rio de Janeiro (RJ). We conducted a randomized block design experiment with two treatments and three replications. For the evaluation of the annual deposition of litter and nutrients (N, P, K, Ca and Mg), we used circular collectors during a year (from July 2006 to June 2007). The planting of Acacia mangium in clay extraction pits contributed with the largest annual deposition of litter and with a litter of better quality compared to Eucalyptus camaldulensis , with higher levels of P and N and lower C:N and polyphenol:N ratios. This fact possibly allows higher rates of decomposition by edaphic microorganisms and, hence, a faster release of these nutrients to the soil. In addition, the planting of legumes showed higher annual deposition of P and N.

Tree Growth, Litter Fall And Leaf Litter Decomposition OfCasuraina equisetifoliaBase Agri-Silviculture System

Tree growth, litter fall and leaf litter decomposition, nutrient return thought leaf litter and litter decomposition were 12 year old Csuraina equisetifolia plantation. The Tree growth under agri-silvicultural system at the beginning of experiment the observations recorded with respect to certain growth parameters of Casuarina equisetifolia have been shown in Table 1 2012–2013. The maximum tree height (14.59 m) found in tree no 4; Dbh (26.22 cm) and canopy width (4.18 m) were recorded in the same tree number 3. Whereas the maximum canopy length (4.32 m) was found in the tree number 3. In the next year 2013–2014 the observations recorded with respect to certain growth parameters at the end of experiment of Casuarina equisetifolia have been shown in Table 2. and the maximum tree height (17.98 m) found in tree no 2; Dbh (28.92 cm) and canopy width (7.04 m) were recorded in the same tree number 3. Whereas the maximum canopy length (7.61 m) was found in the tree number 3. The maximum litter from litter trap was recorded in (68.33 g) month of February during 2012–2013 and the minimum litter from litter traps was found in (27.98 g) month of September during the year 2013–2014.

Mixed leaf litter decomposition and N, P release with a focus on Phyllostachys edulis (Carrière) J. Houz. forest in subtropical southeastern China

As an important non-wood forest product and wood substitute, Moso bamboo grows extremely rapidly and hence acquires large quantities of nutrients from the soil. With regard to litter decomposition, N and P release in Moso bamboo forests is undoubtedly important; however, to date, no comprehensive analysis has been conducted. Here, we chose two dominant species (i.e., &lt;em&gt;Cunninghamia lanceolata&lt;/em&gt; and &lt;em&gt;Phoebe bournei&lt;/em&gt;), in addition to Moso bamboo, which are widely distributed in subtropical southeastern China, and created five leaf litter mixtures (PE100, PE80PB20, PE80CL20, PE50PB50 and PE50CL50) to investigate species effects on leaf litter decomposition and nutrient release (N and P) via the litterbag method. Over a one-year incubation experiment, mass loss varied significantly with litter type (&lt;em&gt;P&lt;/em&gt; &amp;lt; 0.05). The litter mixtures containing the higher proportions (≥80%) of Moso bamboo decomposed faster; the remaining litter compositions followed Olson’s decay mode well (&lt;em&gt;R&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt; &amp;gt; 0.94, &lt;em&gt;P&lt;/em&gt; &amp;lt; 0.001). N and P had different patterns of release; overall, N showed great temporal variation, while P was released from the litter continually. The mixture of Moso bamboo and Phoebe bournei (PE80PB20 and PE50PB50) showed significantly faster P release compared to the other three types, but there was no significant difference in N release. Litter decomposition and P release were related to initial litter C/N ratio, C/P ratio, and/or C content, while no significant relationship between N release and initial stoichiometric ratios was found. The Moso bamboo–&lt;em&gt;Phoebe bournei&lt;/em&gt; (i.e., bamboo–broadleaved) mixture appeared to be the best choice for nutrient return and thus productivity and maintenance of Moso bamboo in this region.

Nitrogen Fertilization Impacts on Phosphorus Cycling in Grazed Grass-Legume Pasture

The impact of different N regimes on P intake and excretion by grazing cattle and P return to soil from feces in a P-enriched pasture was investigated. Six 0.28-ha plots were over seeded with triticale (×Triticosecale rimpaui Wittm.) and crimson clover (Trifolium incarnatum) into tall fescue (Lolium arundinacea)/bermudagrass (Cynodon dactylon). Treatments included: 100% of N in split application, 50% of N in single application, and 0% of N. In summer, plots were over seeded with cowpea (Vigna unguiculata) and fertilizer treatments were applied. Forage intake was estimated from fecal excretion and fecal degradation and nutrient return to soil at 0, 28, 56, 84, and 112 days after application were determined. Forage P was not affected by season or treatment (P > 0.10); forage P mass was greater in cool than warm season. Phosphorus intake and water-soluble P output were not affected (P > 0.10) by season or treatment. Phosphorus output increased (P = 0.087) with increasing N in cool season, but not warm season. Soil P was greater (P < 0.0001) in warm than cool season. Feces remaining, P, and water-soluble P in feces were not affected by N treatment or season, but decreased (P < 0.10) with time. Sufficient P was returned to soil from feces to support forage growth, even in the absence of N fertilization. In a high-P pasture, N did not affect intake and fecal returns of P by cattle, foliar P uptake, nor rate and extent of assimilation of P into soil from feces.

黄土丘陵沟壑区主要草种枯落物的持水能力与养分潜在归还能力

Because of the serious soil erosion,the soil moisture and nutrients deficiency,the slowly recovery and scarcity of natural vegetation in the hill-gully Loess Plateau,the ecological effects of litter layer are particularly important for litter layer effective reduction on surface runoff and mitigate soil erosion. Thus,in this study,the litter accumulation ofcommunities and main herb species in different site conditions was investigated in the hill-gully Loess Plateau,water holding capacity of litter of main herb species was measured by the immersion method,potential nutrient return capacity of litter of main herb species was analyzed by measuring the nutrients content,lignin and cellulose content,then the effects of main species litter on soil fertility improvement was discussed. It' s important to understand the mechanism and efficacy of the resistance of plants to soil erosion. The main results were as follows: 1) the accumulation of community litter was between 73.74—175.26 g / m2,and was significantly different in slope-gully sites( P0. 05),ordered as shady gully slope hilltop sunny gully slope shady hilly slope sunny hilly slope. While in micro-sites ordered as under vegetation ephemeral gully fish-scale pit bare land on the sunny slope,ephemeral gully fish-scale pit under vegetation bare land on the shady slope and under vegetation bare land on the hilltop. 2) The maximal water holding capacity of litter of main species was up to 1.22—4.34 times of its dry mass,and it was extremely significantly different among species( P 0. 01),ordered as the defoliation of Bothriochloa ischaemun the defoliation of Artemisia gmelinii the deadwood of Bothriochloa ischaemun the defoliation of Lespedeza davurica the litter of Stipa bungeanaon the deadwood of Lespedeza davurica the deadwood of Artemisia gmelinii. 3) The organic carbon content( 7. 35% —40. 33%) and total nitrogen content( 0. 61%—1. 60%) of species were extremely significant different among species( P 0. 01),but they were not significantly different in slope-gully sites. 4) Indicators that influenced litter decomposition( such as lignin content,cellulose content,lignin / N ratio,C / N ratio) were extremely significant different among species( P 0. 01). The lignin content( 1.00%—8.20%) and cellulose content( 3. 16%—14. 06%) and lignin / N ratio( 0. 78—12. 48) were extremely significantly different in slope-gully sites( P 0. 05),while C / N ratio( 5.61—57.41) was not significantly different. 5)The potential nutrient return capacity of Artemisia gmelinii defoliation was the highest,followed by the litter of Lespedeza davurica and Bothriochloa ischaemun,and the litter of Stipa bungeanaon was the lowest. In conclusion,the water holding capacity and the potential nutrient return capacity of Bothriochloa ischaemun litter on the sunny slope and the defoliation of Artemisia gmelinii and Lespedeza davurica on the hilltop and shady slope were the highest among species in slope-gully sites,they could effectively improve the soil fertility. While,the litter of Stipa bungeanaon water holding capacity and the potential nutrient return capacity both were the lowest among species in slope-gully sites. The soil fertility effects of different species should be considered when the vegetation was used to control soil erosion. The species should be chosen which not only could control soil erosion but also significantly improve soil fertility,and then the soil quality could be slowly improved.Therefore,Bothriochloa ischaemun,Artemisia gmelinii and Lespedeza davurica were the good choice to control soil erosion on the slopes.

Litterfall and nutrients return in Nothofagus antarctica forests growing in a site quality gradient with different management uses in Southern Patagonia

We evaluated the annual litterfall and nutrients return in primary forests of Nothofagus antarctica growing at three different site classes (SC) (III, IV and V) and compared two of these forests with adjacent stands under silvopastoral use (thinned 40 years ago), in Patagonia, Argentina. Traps were installed in each stand and sampled monthly during the litterfall over 10 years. Sample from the five stands was ground for further analyses of nutrients (N, P, K, Ca, Mg and S). The litterfall varied significantly between SC, but not between years, from 1,306 to 1,972 kg ha−1 in the best site. The nutrients return from litterfall did not change neither between site classes and years in most nutrients. Comparing primary forests with silvopastoral stands, in SCIV, significant differences among uses occurred for litterfall production and nutrients return, being higher in primary forest. While, in SCV, the litterfall and nutrients return practically did not change among uses. The results showed the incidence of site quality and forest use on the litterfall and nutrients return in N. antarctica forests.

Sewage Sludge Usage in Agriculture: a Case Study of Its Destination in the Curitiba Metropolitan Region, Paraná, Brazil

The agricultural destination of sewage sludge promotes the return of organic matter and nutrients to the soil, prevents contamination and degradation of hydric resources, and contributes to food and fiber production. In Brazil, the Resolution of the National Environment Council (Conama 375/06) and in the State of Parana the Resolution of the State Environment Cabinet (Sema 021/09) established criteria and procedures for agricultural use of sewage sludge seeking to avoid risk to public health and the environment. This case study attempts to present the results of the destination of the sludge generated in the Sludge Management Units (SMU) in Curitiba Metropolitan Region (CMR), State of Parana, Brazil from 2007 to 2010. Data analysis of agronomic parameters and inorganic substances (metals) of 99 batches of sewage sludge destined for agricultural use, based on 239 agronomic projects, was performed. The comparison of the characteristics of the batches generated in anaerobic and aerobic SMUs of CMR was also conducted. During the study, 88,166 t of sludge (33,404 dry tons) were destined for 2,288 ha of agricultural areas. The sludge provided 88 % of the lime, 74 % of N, 73 % of P2O5, and 35 % of K2O for fertilizing the corn, soybean, bean, oat, wheat, green manure, and in the implementation and postharvest of stone fruit trees. The 80 benefited farmers reduced expenses with fertilizers and limestone, saving an average of US$813.45 per ha.

Organic matter dynamics and microbial activity during decomposition of forest floor under two native neotropical oak species in a temperate deciduous forest in Mexico

Litter decomposition, which represents the main pathway of nutrient return to soil, affects the fertility of forest fragments. The biochemical composition of litter and the way that it decomposes are determined by the physiological characteristics of the plant species from which the material is derived. The main physiological process affecting nutrient concentrations in litter is the resorption of foliar nutrients. In this study, we determined organic matter composition, nutrient dynamics and microbial activity in samples of forest floor litter collected over a two year period under two native oak species, Quercus castanea (Qc) and Quercus deserticola (Qd), growing in a semi-natural deciduous forest in central Mexico. These coexisting oak species differ in relation to nutrient resorption efficiency, and their spatial distribution is vulnerable to climate change. The Nuclear Magnetic Resonance (13C-NMR) spectra revealed a higher O-alkyl:aromatic C ratio and more decomposable lignin structure (based on lignin subunit ratios) in the Qd litterfall than in the Qc litterfall (3.7 and 3.6, respectively), in concordance with results obtained by Fourier Transform Infrared (FTIR) Spectroscopy and Differential Scanning Calorimetry (DSC). Consequently, the Qd litter had a higher proportion of thermolabile compounds. In the same way, the nutrient concentrations were very different in each species, as a result of the different patterns of foliar nutrient resorption: both nutrient concentrations and microbial activity were higher in the Qd litter than in the Qc litter. Moreover, the specific enzymatic activity (SEA) of the microbial community was higher in the Qc litter, suggesting that these microorganisms required investment of more energy to increase nutrient acquisition rather than to increase microbial growth. The results suggest that the chemical composition and chemical quality of litterfall, resulting from foliar resorption, strongly affect forest floor microbial activity. Consequently, the physiological footprint of both tree species is a key factor in decomposition processes and soil fertility.

Litterfall production and nutrient return in different-aged Chinese fir (Cunninghamia lanceolata) plantations in south China

Litterfall production and nutrient return in different-aged Chinese fir (Cunninghamia lanceolata) plantations in south China

Nutrient cycling in tropical pasture ecosystems

In most forage production systems, essential nutrients required for plant growth are provided by different pools in the ecosystem. In general, warm-climate grasslands are characterized by extensive grazing systems with minimal inputs of commercial fertilizer and supplemental feed, primarily because of unfavorable economics of fertilization or limited availability of fertilizer material. Low soil N availability is a major limitation in tropical and subtropical pasture systems, and it represents one of the main causes of pasture degradation. The major pools of N in grazed grasslands are soil, vegetation, grazing animals, and atmosphere. Fluxes among the various pools are complex and are affected by biotic and abiotic factors such as climate, soil organisms, forage species, and herbivores. Therefore, nutrient cycling is a vital component in maintaining pasture sustainability because it represents an important source of nutrients to warm-season grass pastures. Excreta and litter are the two major pathways for herbage nutrients to return to the soil. Litter quantity and chemical composition are determinants in litter deposition and decomposition and are greatly affected by grazing management practices. The use of warm-season legumes in warm-season grass stands is a potential management practice that can improve litter decomposition and N inputs to warm-season grass pastures. Approximately 70 to 90% of the nutrients consumed by ruminants return to the pastures via excreta deposition; however, nutrient return through excreta is not uniform. Stocking method, portable shade and water systems, and strategic fencing are effective management practices to improve excreta distribution on pastures. The adoption of management practices that improve nutrient cycling is a determining factor to reduce warm-season grass pasture degradation and optimize productivity and persistence.

Crop residue management and soil health: A systems analysis

Due to the scarcity of alternative organic amendments, the retention of crop residue in fields can be considered key in promoting physical, chemical, and biological attributes of soil health in agricultural systems of developing countries. However, due to multiple other uses, small landholders in these countries are faced with trade-offs in managing crop residues. This article reviews crop residue management practices, mainly surface retention, incorporation or removal, describing their advantages and limitations in cereal-based agroecosystems in developing countries. The benefits of residue retention are regionally variable and depend on both agroclimatic and socioeconomic factors. Most studies from developing countries in Asia, Latin America, and Africa show positive effects of retaining crop residues on soil quality, soil organic matter and carbon storage, soil moisture retention, enhanced nutrient cycling, and decreased soil loss, among other environmental and soil health benefits. Variation was observed in the effect of surface retention vs. incorporation on various soil properties indicating the importance of taking into account abiotic factors such as climate, soil texture, study duration, sampling methods, and agronomic practices when assessing the impact of these practices. Negative effects of residue retention on crop performance attributed to nitrogen immobilization, waterlogging and decreased soil temperature have also been reported in some environments. Residue trade-offs in mixed crop-livestock systems in developing countries can limit the amount of residue retained. However, interventions such as intensification, partial retention, improved return of nutrients from manures, and the provision of substitutes to the current functions of livestock (e.g. mechanization, insurance) could reduce these residue trade-offs in favour of promoting long-term soil health.

The significance of Shuidonggou Locality 12 to studies of hunter-gatherer adaptive strategies in North China during the Late Pleistocene

The effect of rapid climate change during the Late Upper Paleolithic on hunter-gatherers is attested by a variety of signals in the archaeological record. One of these, the spread of the microblade technology in North China, shows a particularly close relationship with climate change. The appearance of microblades and functionally related bone and ground stone technology at SDG12 is particularly revealing of this Late Pleistocene adaptive diversification in North China. SDG12 and other records suggest that microblade technology flourished in harsh environments that demanded high residential mobility. That in addition to their use in hunting weaponry, microblades were used in manufacturing the sophisticated cold weather clothing required for winter mobility, is shown by the presence of bone needles and a bone knife handle slotted to accept microblades. The SDG12 fauna and ground stone indicate an attendant shift from a more large game dominated, to a more plant and small game dominated diet that included net hunting and demanded a variety of production tasks that included net-making (spinning) and extensive stone boiling to maximize nutrient returns and as a step in manufacturing. We suspect these changes are the root cause of subsequent changes in social structure.

Litter Decomposition of Signalgrass Grazed with Different Stocking Rates and Nitrogen Fertilizer Levels

Litter decomposition is an important pathway of nutrient return on grazed pastures and it may be affected by management practices. The objective of this study was to evaluate the effects of stocking rate (2, 3.9, and 5.8 AU ha−1; 1 AU = 450 kg animal live weight) and N fertilization level (0, 150, and 300 kg N ha−1 yr−1) on signalgrass (Brachiaria decumbens Stapf.) litter decomposition. Signalgrass litter was placed in nylon bags and incubated for 0, 4, 8, 16, 32, 64, 128, and 256 d during 2009 and 2010. Litter decomposition rates differed between years and among incubation times. The decomposition rate was less in 2009 than in 2010 (3.46 and 4.20 mg g−1d−1, respectively). Stocking rate had no effect on litter decomposition rate. Decomposition rates were greater for fertilization with 300 vs. 0 kg N ha−1 yr−1 (4.47 vs. 3.29 mg g−1 d−1, respectively), which resulted in less N remaining in fertilized signalgrass litter. Concentrations of N and lignin as well as lignin/N ratio fit linear plateau models, increasing 7, 151, and 25 g kg−1, respectively, during the 256‐d incubation period. The effect of year on residual N and C/N ratios highlighted the need for long‐term trials that measure the peaks of nutrient release and availability to plants. Data are needed to guide nutrient management decisions in tropical pastures. Pasture N fertilization may shift the balance between litter immobilization/mineralization, altering N dynamics in the litter pool.