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The biotic release of nitric oxide (NO), a greenhouse gas, into the atmosphere contributes to climate change. In plants, NO plays a significant role in metabolic and signaling processes. However, little attention has been paid to the plantborne portion of global NO emissions. Owing to the growing significance of global flooding events caused by climate change, the extent of plant NO emissions has been assessed under low-oxygen conditions for the roots of intact plants. Each examined plant species (tomato, tobacco, and barley) exhibited NO emissions in a highly oxygen-dependent manner. The transfer of data obtained under laboratory conditions to the global area of farmland was used to estimate possible plant NO contribution to greenhouse gas budgets. Plant-derived and stress-induced NO emissions were estimated to account for the equivalent of 1 to 9% of global annual NO emissions from agricultural land. Because several stressors induce NO formation in plants, the actual impact may be even higher. [ABSTRACT FROM AUTHOR]

A greenhouse experiment with sorghum sudangrass (Sorghum bicolor × Sorghum sudanense) and maize (Zea mays) was conducted to assess information on differences in their nitrogen and fertilizer utilization when used as energy crops. The aim was to contribute to the scarce data on sorghum sudangrass as an energy crop with regards to nitrogen derived from fertilizer (NdfF) in the plant's biomass and fertilizer nitrogen utilization (FNU). Sorghum sudangrass and maize were each grown in eight bags of 45 L volume and harvested at maturity after 154 days. Each crop treatment was further divided in a control treatment (four bags each) that did not receive N fertilization and a fertilization treatment (four bags each) that received 1.76 g N, applying a 15N-labelled liquid ammonium nitrate fertilizer. Fertilization took place at the start of the experiment. After harvest, the whole plant was divided in the fractions "aboveground biomass" (ABM) and "stubble + rootstock" (S + R). Weight, N content and 15N content were recorded for each fraction. In addition, N content and 15N content were assessed in the soil before sowing and after harvest. The experiment showed that FNU of sorghum sudangrass (65%) was significantly higher than that of maize (49%). Both crops accumulated more soil N than fertilizer N. The share of fertilizer N on total N uptake was also higher with sorghum sudangrass (NdfF = 38%) compared to maize (NdfF = 34%). The observations made with our control plant (maize), showed that the results are plausible and comparable to other 15N studies on maize regarding yields, NdfF, and FNU, leading to the assumption that results on sorghum sudangrass are plausible as well. We therefore conclude that the results of our study can be used for the preliminary parametrization of sorghum sudangrass in soil organic matter (SOM) balance at field level. [ABSTRACT FROM AUTHOR]

The intensification of food production systems has resulted in landscape simplification, with trees and hedges disappearing from agricultural land, principally in industrialized countries. However, more recently, the potential of agroforestry systems and small woody landscape features (SWFs), e.g., hedgerows, woodlots, and scattered groups of trees, to sequester carbon was highlighted as one of the strategies to combat global climate change. Our study was aimed to assess the extent of SWFs embedded within agricultural landscapes in Germany, estimate their carbon stocks, and investigate the potential for increasing agroforestry cover to offset agricultural greenhouse gas (GHG) emissions. We analyzed open-source geospatial datasets and identified over 900,000 hectares of SWFs on agricultural land, equivalent to 4.6% of the total farmland. The carbon storage of SWFs was estimated at 111 ± 52 SD teragrams of carbon (Tg C), which was previously unaccounted for in GHG inventories and could play a role in mitigating the emissions. Furthermore, we found cropland to have the lowest SWF density and thus the highest potential to benefit from the implementation of agroforestry, which could sequester between 0.2 and 2 Tg of carbon per year. Our study highlights that country-specific data are urgently needed to refine C stock estimates, improve GHG inventories and inform the large-scale implementation of agroforestry in Germany. [ABSTRACT FROM AUTHOR]

SUMMARY: Agroforestry systems (AFS) can serve to decrease ecosystem carbon (C) losses caused by deforestation and inadequate soil management. Because of their shade tolerance, cacao plants are suitable to be grown in AFS, since they can be combined with other kinds of trees and shrubs. The potential for C sequestration in cacao farming systems depends on various factors, such as management practices, stand structure and plantation age. We compared conventionally and organically managed cacao monoculture systems (MCS) and AFS in Sara Ana (Bolivia) with respect to C stocks in plant biomass and to amounts of litterfall and pruning residues. The total aboveground C stocks of the AFS (26 Mg C ha−1) considerably exceeded those of the MCS (~7 Mg C ha−1), although the biomass of cacao trees was greater in the MCS compared to the AFS. Due to higher tree density, annual litterfall in the AFS (2.2 Mg C ha−1 year−1) substantially exceeded that in the MCS (1.2 Mg C ha−1 year−1). The amounts of C in pruning residues (2.6 Mg C ha−1 year−1 in MCS to 4.3 Mg C ha−1 year−1 in AFS) was more than twice those in the litterfall. Annual nitrogen (N) inputs to the soil through pruning residues of cacao and N-fixing trees were up to 10 times higher than the N inputs through external fertiliser application. We conclude that appropriate management of cacao AFS, involving the pruning of leguminous trees, will lead to increases in biomass, litter quantity and quality as well as soil C and N stocks. Thus, we recommend stimulating the expansion of well-managed AFS to improve soil fertility and enhance C sequestration in soils. [ABSTRACT FROM AUTHOR]

Abstract Farmers expect yield reduction of cash crops like cocoa when growing in agroforestry systems compared to monocultures, due to competition for resources, e.g. nutrients and water. However, complementarities between species in the use of resources may improve resource use efficiency and result in higher system performance. Cocoa trees have a shallow rooting system while the rooting characteristics of the associated trees are mainly unknown. This work investigates fine root distribution and production in five cocoa production systems: two monocultures and two agroforestry systems under conventional and organic farming, and a successional agroforestry system. In the organic systems a perennial leguminous cover crop was planted and compost was added, while herbicides and chemical fertilizers were applied in the conventional ones. We measured cocoa fine root parameters in the top 10 cm of soil and annual total fine root production at 0–25 and 25–50 cm depth. We related the root data with both the aboveground performance (tree and herbaceous biomass), and the cocoa and system yields. Cocoa fine roots were homogenously distributed over the plot area. Around 80% of the total fine roots were located in the upper 25 cm of soil. The total fine root production was 4-times higher in the agroforestry systems and the organic monoculture than in the conventional monoculture. The roots of the associated tree species were located in the same soil space as the cocoa roots and, in principle, competed for the same soil resources. The cocoa yield was lower in the agroforestry systems, but the additional crops generated a higher system yield and aboveground biomass than the conventional cocoa monocultures, implying effective resource exploitation. The leguminous cover crop in the organic monoculture competed with the cocoa trees for nutrients, which may explain the lower cocoa yield in this system in contrast with the conventional monoculture. Graphical abstract Unlabelled Image Highlights • Fine roots are concentrated in the topsoil implying competition between species. • Cocoa fine root parameters were not affected by species interactions. • Belowground competition reduces cocoa growth and yield in agroforests. • Agroforests have higher system yield and biomass than monocultures. [ABSTRACT FROM AUTHOR]

Context Structural characteristics of tree stands such as species diversity, tree density, and stratification can affect throughfall and microclimate. Pruning changes the canopy and may therefore modulate internal conditions. Aims The aim of this study is to assess the environmental growing conditions of cocoa trees. Methods We monitored canopy openness and the impact of stand structure on throughfall and microclimate in three cocoa production systems (monoculture, agroforestry, and successional agroforestry) and a natural regrowth in a long-term trial in Bolivia from 2013 to 2015. We further focused on the effect of annual shade tree and cocoa pruning on these variables to evaluate the potential impact of this activity. Results Agroforestry systems buffered extreme climate events like temperature fluctuations compared to monocultures but reduced light and throughfall drastically. Spatial variability of throughfall and transmitted light were low under a high and closed shade tree canopy. Shade tree pruning resulted in higher canopy openness, light transmittance, and throughfall, while the buffer function of the agroforestry systems concerning temperature and humidity fluctuations was reduced. Conclusion Differences between cocoa production systems regarding throughfall and microclimate were overlain by pruning activities. Cocoa agroforestry systems are temporal dynamic systems. Pruning timing and intensity is pivotal for balancing light and water availability under seasonally varying environmental conditions to conserve micro-environments for cocoa production with less exposure to unfavorable climate. [ABSTRACT FROM AUTHOR]

Soil moisture has high spatial and temporal variability, depending on topography, soil texture, vegetation and meteorological conditions. It influences many processes in the soil and supplies water to the vegetation. This is often a limiting factor in agricultural production. Over an 18-month period, we measured soil moisture dynamics down to a depth of 70 cm in a long-term trial in Bolivia comprising six different land-use systems, i.e. cocoa monocultures and agroforestry systems, both under organic and conventional management, successional cocoa agroforestry systems and a natural fallow. Soil was heterogeneous over the area and in depth. We identified and separated two soil groups which differed in both, texture and soil water retention capacity. Considering the two groups, we assessed the effect of the different land-use systems on soil moisture dynamics and plant available water on the one hand, and how different soil moisture conditions affect growth and production of cocoa on the other. In monocultures with shallow rooting cocoa only, soil moisture decreased mainly in the uppermost soil layer during the dry season and the lower layers kept more moisture year round. In agroforestry systems soil moisture decreased homogeneously over the soil profile, implying a complementarity in water use of cocoa and deeper rooting trees. The uppermost soil layer in the agroforestry systems had higher soil moisture than in the monoculture, demonstrating the role of shade trees to reduce water loss from top soil by evaporation and transpiration of the cocoa. Even though one soil group had continuously higher water availability than the other group, we did not find an effect on the cocoa yield. Cocoa relies on sufficient water supply, but beside information on the precipitation it is important to know the soil structure and soil water retention capacity when discussing water availability for cocoa production and to consider the heterogeneity of the soil even over small area. [ABSTRACT FROM AUTHOR]

• Alley cropping systems show reduced wind speed, light intensity and surface runoff. • Effect on other parameters varies with the design and orientation of the tree rows. • Soil moisture showed the highest variability within and among studies. Climate change scenarios predict an increased occurrence of droughts and heatwaves, as well as extreme rainfall events in Central Europe. Alley cropping, which is the inclusion of rows of trees and shrubs in agricultural land, could enhance the resilience of cropping systems, as these systems are expected to positively modify the microclimate and water balance of croplands. This review analyses the effect of alley cropping on the microclimate and water balance, based on the available evidence from temperate alley cropping systems. Within alley cropping systems, the tree rows generate gradients in microclimatic variables, whereby strongest effects are observed in or close to the tree rows. Field-scale studies on light intensity (n =20), wind speed (n =4) and surface runoff (n =3) all reported a reduction compared to sole cropping systems. Effects on air temperature (n =10), relative humidity (n =5) and evapotranspiration (n =6) varied among studies, with the majority reporting a decrease in daytime temperatures (50% of studies), variable effects on relative humidity (60%) and an increase in evapotranspiration (50%) due to higher evapotranspiration by trees. Highest variation among studies was found for soil moisture, with 41% of studies reporting temporal and spatial differences within the system. This variation among studies likely depends on the purpose of the trees (short rotation coppice vs. fruit and/or timber trees) and design of the system. Also site context, such as topography, landscape diversity and climate, could play a role, but these factors are rarely taken into account. Only few studies investigated landscape-scale effects (n =3), such as groundwater recharge and moisture recycling. Future research should investigate the role of site context in the functioning of alley cropping systems and quantify landscape-scale effects. The process understanding gained from those studies will contribute to designing alley cropping systems that enhance the climate change resilience of current central European cropping systems. [Display omitted] [ABSTRACT FROM AUTHOR]