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Differences in the density of conspecific tree individuals in response to environmental gradients are well documented for many tree species, but how such density differences are generated and maintained is poorly understood. We examined the segregation of six dipterocarp species among three soil types in the Pasoh tropical forest, Malaysia. We examined how individual performance and population dynamics changed across the soil types using 10-year demographic data to compare tree performance across soil types, and constructed population matrix models to analyze the population dynamics. Species showed only minor changes in mortality and juvenile growth across soil types, although recruitment differed greatly. Clear, interspecific demographic trade-offs between growth and mortality were found in all soil types. The relative trade-offs by a species did not differ substantially among the soil types. Population sizes were projected to remain stable in all soil types for all species with one exception. Our life-table response experiment demonstrated that the population dynamics of a species differed only subtly among soil types. Therefore, species with strong density differences across soil types do not necessarily differ greatly in their population dynamics across the soil types. In contrast, interspecific differences in population dynamics were large. The trade-off between mortality and growth led to a negative correlation between the contributions of mortality and growth to variations in the population growth rate (λ) and thus reduced their net contributions. Recruitment had little impact on the variation in λ. The combination of these factors resulted in little variation in λ among species.

Upland forests are traditionally thought to be net sinks for atmospheric methane (CH4). In such forests, in situ CH4 fluxes on tree trunks have been neglected relative to soil and canopy fluxes. We measured in situ CH4 fluxes from the trunks of living trees and other surfaces, such as twigs and soils, using a static closed-chamber method, and estimated the CH4 budget in a temperate upland forest in Beijing. We found that the trunks of Populus davidiana emitted large quantities of CH4 during July 2014–July 2015, amounting to mean annual emissions of 85.3 and 103.1 μg m−2 h−1 on a trunk surface area basis on two replicate plots. The emission rates were similar in magnitude to those from tree trunks in wetland forests. The emitted CH4 was derived from the heartwood of trunks. On a plot or ecosystem scale, trunk CH4 emissions were equivalent to c. 30–90% of the amount of CH4 consumed by soils throughout the year, with an annual average of 63%. Our findings suggest that wet heartwoods, regardless of rot or not, occur widely in living trees on various habitats, where CH4 can be produced.

Global budgets ascribe 4–10% of atmospheric methane (CH4) sinks to upland soils and have assumed until recently that soils are the sole surface for CH4 exchange in upland forests. Here we report that CH4 is emitted from the stems of dominant tree species in a temperate upland forest, measured using both the traditional static-chamber method and a new highfrequency, automated system. Tree emissions averaged across 68 observations on 17 trees from May to September were 1.59 ± 0.88 μmol CH4m−2 stem h−1 (mean ± 95% confidence interval), while soils adjacent to the trees consumed atmospheric CH4 at a rate of −4.52 ± 0.64 μmol CH4m−2 soil h−1 (P < 0.0001). High-frequency measurements revealed diurnal patterns in the rate of tree-stem CH4 emissions. A simple scaling exercise suggested that tree emissions offset 1–6%of the growing season soil CH4 sink and may have briefly changed the forest to a net CH4 source.

BACKGROUND AND AIMS: The combined effects of (1) reduced soil moisture availability, (2) reduced application of inorganic fertilisers while incorporating straw, (3) soil type, and their effects on growth, root system plasticity, phosphorus (P) nutrition of rice, and soil P dynamics are poorly known, but very important when aiming to increase the efficiency of water and P use. METHODS: Using large pots a three-factor factorial experiment was conducted with two moisture treatments (i.e. continuous flooding, and draining of top soil after flowering while subsoil was kept moist through capillary action), three fertilisation treatments; with (P1) and without (P0) applications of inorganic P fertilisers, and 25 % of inorganic fertilisers reduced while incorporating straw (5 t ha⁻¹), and soil type (i.e. clay and sandy soils with 15 and 9 mg P kg⁻¹ soil, respectively in P0). Shoot and root growth, root system plasticity, P nutrient status and soil P dynamics were measured. KEY RESULTS: Straw incorporation with reduced inorganic fertiliser application ensured a higher shoot dry weight and yield only in flooded clay soil as compared with P0 and P1, and a similar shoot dry weight and yield to P1 under drained clay soil. A positive growth response was facilitated by an increased water-use efficiency and rate of photosynthesis in shoots, and increased root system plasticity through the production of greater root length, more roots in deep soil layers, and an increased fraction of fine roots. Straw enhanced P extractability in soil. Drained soil reduced P uptake (15–45 %) and increased P-use efficiency. In addition to the re-translocation of P from senescing leaves and stems under both moisture conditions, the P concentration in green leaves under drained condition was also reduced (41–72 %). CONCLUSION: Growth benefits of straw incorporation were observed in clay soil under both moisture conditions, and this was facilitated by the improved P availability, increased P uptake, and greater root system plasticity with the production of deeper and finer roots, compared with that in sandy soil, and inorganic fertiliser applications alone. As P uptake was reduced under drained soil, P re-translocation and % P allocated to panicles increased.

Conservation agriculture involves reduced tillage, permanent soil cover and crop rotations to enhance soil fertility and to supply food from a dwindling land resource. Recently, conservation agriculture has been promoted in Southern Africa, mainly for maize-based farming systems. However, maize yields under rain-fed conditions are often variable. There is therefore a need to identify factors that influence crop yield under conservation agriculture and rain-fed conditions. Here, we studied maize grain yield data from experiments lasting 5 years and more under rain-fed conditions. We assessed the effect of long-term tillage and residue retention on maize grain yield under contrasting soil textures, nitrogen input and climate. Yield variability was measured by stability analysis. Our results show an increase in maize yield over time with conservation agriculture practices that include rotation and high input use in low rainfall areas. But we observed no difference in system stability under those conditions. We observed a strong relationship between maize grain yield and annual rainfall. Our meta-analysis gave the following findings: (1) 92% of the data show that mulch cover in high rainfall areas leads to lower yields due to waterlogging; (2) 85% of data show that soil texture is important in the temporal development of conservation agriculture effects, improved yields are likely on well-drained soils; (3) 73% of the data show that conservation agriculture practices require high inputs especially N for improved yield; (4) 63% of data show that increased yields are obtained with rotation but calculations often do not include the variations in rainfall within and between seasons; (5) 56% of the data show that reduced tillage with no mulch cover leads to lower yields in semi-arid areas; and (6) when adequate fertiliser is available, rainfall is the most important determinant of yield in southern Africa. It is clear from our results that conservation agriculture needs to be targeted and adapted to specific biophysical conditions for improved impact.

Urban lawn ecosystems are widespread across the United States, with fertilization rates commonly exceeding plant nitrogen (N) uptake rates. While urban soils have been shown to accumulate C and N over time, the long-term balance of N inputs and losses from lawn soils remains largely uncertain. We sampled residential lawn soils aged 7–100 years in the Salt Lake City metropolitan area as a means of inferring changes in total nitrogen (TN) content, organic carbon (OC) content, C:N ratio, and δ¹⁵N of bulk soil over time. Core-integrated (0–40 cm) TN and OC stocks increased linearly by 2.39 g N m⁻² year⁻¹ and 29.8 g OC m⁻² year⁻¹ over the 100-year chronosequence. TN and OC percent were also negatively correlated with elevation. Multiple linear regression models including housing age and elevation as covariates, explained 68 and 62% of variability in TN and OC stocks respectively. δ¹⁵N increased with housing age, soil depth, and clay content, suggesting N removal over time, especially in poorly drained soils. We quantified potential hydrologic and gaseous N losses over time by comparing observed N accumulation to different historic fertilization scenarios. Modeling and isotopic results suggest that, while soil N has accumulated over time, the majority of N added to lawns in the Salt Lake Valley over 50 years of fertilization was likely lost from surface soils via denitrification or leaching.

Background and aims Although plants are recognized as conduits for soil-produced N2O, little is known about N2O fluxes from mature trees under field conditions as well as their contribution to total (soil + stem) N2O fluxes. Exclusion of tree-mediated N2O may thus underestimate total forest N2O fluxes. In the present study, our aims were to quantify tree-mediated N2O emissions and their seasonal patterns. Methods We investigated in situ stem and soil N2O fluxes from mature alder trees on poorly-drained soil and mature beech and spruce trees on well-drained soils during March–October 2015. Results Alder, beech and spruce consistently emitted N2O via stems and all displayed clear seasonal patterns. Soil and air temperature, vapor pressure deficit, and soil N2O concentration influenced the temporal variability of stem N2O fluxes. Stem and soil N2O fluxes from the alder stand were higher than beech and spruce stands. Stem N2O fluxes accounted 8.8–9.8% of the total N2O fluxes in the beech and spruce stands but only 1.1% in the alder stand. Conclusions Our study reveals the importance of field-based measurements across seasons in order to come up with reliable estimates of stem N2O fluxes. N2O estimates from temperate forests that are solely based on soil N2O flux measurements are probably conservative.

Corn yield (Zea mays L.) and economic return with different tillage systems and crop rotations are highly influenced by regional soil and climate conditions. This study was conducted at seven locations in Iowa from 2003 to 2013. The experiment design was split‐plot with tillage as the main factor, which included five tillage systems (no‐tillage, NT; strip‐tillage, ST; chisel plow, CP; deep rip, DR; and moldboard plow, MP).Three crop rotations of corn–soybean (Glycine max L.), C–S; corn–corn–soybean, C–C–S; and corn–corn, C–C were subplots in a completely randomized block design in four replications. The objectives were to: (i) investigate seasonal variability in corn yield as affected by tillage and crop rotation, (ii) identify appropriate tillage for each crop rotation and location, and (iii) evaluate the magnitude of crop rotation effect on corn yield. Corn yields varied from 2.5 to 15.8 Mg ha−1 with no detectable increase over time. The results showed northern locations have yield of 1.9 Mg ha−1 and economic return of US$329 ha−1 advantage over southern locations. Yield and economic returns for the three rotations were as follow: C–S > C–C–S > C–C. Yield and economic penalty were greater with NT than conventional tillage in the northern locations (poorly‐drained soils) than locations with well‐drained soils. The corn yield penalty associated with C–C was location specific and varied from 11 to 28%. The findings suggest a location specific adoption of tillage and crop rotation for achieving optimum yield.

Background Grassland reseeding typically requires intensive tillage. This disrupts soil nutrient dynamics, especially under varying drainage conditions. Methods This study evaluated the combined effects of tillage legacy, drainage and soil depth on key soil properties within a long‐term grassland experiment. Treatments compared two no‐tillage durations (5 years of no tillage, 5YNT; 30 years of no tillage, 30YNT), two drainage systems (drained and undrained) and two depths (0–10 and 10–30 cm) following reseeding. Total carbon (TC), total nitrogen (TN), total phosphorus (TP) and pH were measured. Results Significant three‐way interactions were detected for all variables. At 0–10 cm, undrained 30YNT plots showed 69% greater TC and 66.9% higher TP than the lowest values recorded in 5YNT × drained combinations at 10–30 cm. TN followed a similar pattern, with substantial enrichment under long‐term no‐tillage. Reseeding reduced TC, TN and TP within 5 years, particularly in surface soils, with the largest proportional losses in undrained plots where nutrient concentrations had been high prior to tillage. Conclusions Findings highlight the importance of conserving long‐term no‐tillage systems to enhance nutrient retention and promote sustainable grassland productivity. Conventional tillage of nutrient‐rich pastures should be avoided to prevent major nutrient losses. Effect of three‐way interaction between soil tillage, drainage and depths on soil properties in reseeded pastures.

Optimal stewardship of fertilizer N is necessary to reduce the effects of reactive N on the environment. However, insufficient information on fertilizer fate and N use efficiency is available for tall fescue [Schedonorus arundinaceus (Shreb.) Dumort.] seed crops. Furthermore, changing weather patterns can lead to increasingly early spring N applications. A field trial using 15N‐labeled urea applied at three spring timings (Early, Late, and Split) was implemented at three locations in western Oregon representing different soil drainage levels. We hypothesized that Early applications on the location having a poorly drained soil would lead to the highest fertilizer N losses and the lowest fertilizer N recovery efficiency (REN) at harvest. The REN was not affected by application timing or location and averaged 57%. Overall, 91% of fertilizer was recovered in the soil–plant system at harvest, with 24% remaining in the soil (0–45 cm), almost all in the organic pool, and 10% remaining in belowground (roots and crowns) biomass. Six months after harvest (i.e., 1 yr after application), total fertilizer recovery in the plant–soil system was unchanged. Spring fertilizer contributed only 31% of aboveground N content at harvest, indicating that N sources outside of spring fertilizer applications supplied most of plant N demand. Combined, our results suggest that fertilizer rates could be reduced and that historical N applications may be leading to elevated soil N and N cycling. Further, we show preliminary evidence that roots and crowns can play an important role in cycling fertilizer N in tall fescue seed systems. Core Ideas Spring N was applied in tall fescue grown for seed at three spring timings: Early, Late, and Split. N uptake and fertilizer loss was independent of application timing or location. At harvest, 57% of fertilizer was recovered in aboveground biomass, and 9% was lost. One year after fertilization, 24% of fertilizer was still in the soil (0‐45 cm). Fertilizer rate can be reduced to avoid N losses in subsequent seasons.