Subtropical Agroecosystem Research Articles

Assessment of Soil Specific Enzyme Activities in Aggregates Size Fractions: a Case Study from Subtropical Agro-ecosystem

Assessment of Soil Specific Enzyme Activities in Aggregates Size Fractions: a Case Study from Subtropical Agro-ecosystem

Nitrogen release dynamics of cover crop mixtures in a subtropical agroecosystem were rapid and species-specific

Nitrogen release dynamics of cover crop mixtures in a subtropical agroecosystem were rapid and species-specific

Long Term of Soil Carbon Stock in No-Till System Affected by a Rolling Landscape in Southern Brazil

In the 1960s, a conservationist agricultural practice known as a “no-tillage system” was adopted. Several benefits such as soil erosion reduction and soil carbon sequestration, among others, could be ascribed to no-till systems. Therefore, it is important to evaluate the long-term sustainability of this agricultural system in different environments. This study has the objective to evaluate the soil organic carbon dynamic in a no-till system (40-year) and on a rolling landscape in Southern Brazil. A systematic grid with four transversal–longitudinal transects was used for soil sampling. Soil samples from 0–20, 20–40, and 40–60 cm depths were collected (16 trenches × 3 depths × 1 sample per soil layer = 48), and a forest nearby was used as control (4 trenches × 3 depths × 1 sample = 12). The soil at the forest site showed 20% more carbon stock than no-till at the 0–20 cm soil depth. However, the entire no-till soil profile (0–60 cm) showed similar soil carbon as forest soil. The soil carbon stock (0–20 cm) in no-till was depleted at a rate of 0.06 kg C m−2 year−1, summing up to a carbon loss of 2.43 kg C m−2. In addition, the non-uniform hillslope affected the soil carbon redistribution through the landscape, since the convex hillslope was more depleted in carbon by 37% (15.87 kg C m−2) when compared to the concave sector (25.27 kg C m−2). On average, the soil carbon loss in the subtropical agroecosystem was much lower than those reported in literature, as well as our initial expectations. In addition, the no-till system was capable of preserving soil carbon in the deepest soil layers. However, presently, the no-till system is losing more carbon in the topsoil at a rate greater than the soil carbon input.

Biochar enhances multifunctionality by increasing the uniformity of energy flow through a soil nematode food web

Soil multifunctionality is the consequence of biotic interactions that drive decomposition, nutrient cycling and net primary production. Energy flux describes the energy consumed and transferred among multitrophic groups in the soil food web, which are logically linked to multifunctionality. In a subtropical agroecosystem with an annual sweet potato-oilseed rape rotation, we explored how biochar and synthetic fertilizer jointly affected agroecosystem multifunctionality (e.g., crop production, soil carbon storage and nutrient cycling) and the energetic structure of the nematode food web during two consecutive years. Results showed that biochar increased soil multifunctionality by 37–110% mainly by promoting a uniform energy flow through the soil nematode food web, which was largely due to increased energy fluxes of fungivores and omnivores-carnivores at the expense of decreased energy flux through herbivores. Applying a lower rate of synthetic fertilizer led to non-uniform energy flow in the soil nematode food web, suggesting that nitrogen limitation could offset the stimulatory effect of biochar on soil multifunctionality. This was because biochar induced oligotrophic conditions (a stoichiometry-induced nitrogen limitation), effectively warranting that continuous biochar application would aggravate nutrient limitations to crops, especially when low rates of synthetic fertilizer are applied. Notably, soil nutrient impoverishment could lead to resource reallocation from aboveground shoot to belowground root production, thereby fueling the energy flow through the herbivore channel. Our findings highlight the importance of balancing biochar and synthetic fertilizer applications to sustain a stable energetic structure in soil nematode food webs, which are associated with greater crop production and soil health in subtropical region.

Integrated analysis of changes in soil microbiota and metabolites following long-term fertilization in a subtropical maize-wheat agroecosystem

Although the application of inorganic fertilizer is a widespread agronomic practice used to boost soil productivity and crop yields, the effects on soil microbiome and the metabolic mechanisms involved in the high-yield response of crops to long-term fertilization remain poorly described. In this study, combined metagenomic and metabolomic analyses were used to explore the mechanism of crop yield response to the 20-year application of nitrogen-phosphorus-potassium fertilizers in a subtropical agroecosystem in Southwest China. Soil bacterial and fungal communities were monitored using 16S rRNA (bacteria) and internal transcribed spacer 1 (ITS1) full-length gene (fungi) amplicon sequencing technologies, and metabolites were detected using a liquid chromatograph mass spectrometer. The results revealed that, in addition to providing nutrients, long-term fertilization shaped the compositions of bacteria and fungi to increase crop yields. Long-term fertilization significantly increased the relative abundances of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi and promoted the secretion of soil metabolites such as carbohydrates, organic acids, and organic nitrogen compounds, which were primarily enriched in amino acid metabolism pathways. The increases in carbon and nitrogen sources and bioactive substances in soil promoted the increases in plant biomass and thereby maintained soil quality and production capacity. The findings highlighted the importance of soil metabolites in maintaining soil productivity as well as crop yields, and suggested that regulating key metabolites could increase crop yields in agroecosystems.

Mulch Application and Plant Spacing Influence on Growth Traits, Pests, Insects and Weeds in Cotton (Gossypium hirsutum L.) Varieties

Mulch Application and Plant Spacing Influence on Growth Traits, Pests, Insects and Weeds in Cotton (Gossypium hirsutum L.) Varieties

Long-Term Effects of Animal Manures on Nutrient Recovery and Soil Quality in Acid Typic Hapludalf under No-Till Conditions

No-till farming and manure application are means of storing carbon in soil and increasing soil quality. However, the organic fertilization of no-till soils may sustain subtropical agroecosystems for only a limited period until the soil quality declines. The C, N, P, and other nutrient cycles are perturbed due to the nutrient imbalance in manures and their application on the soil surface, which poses a risk for nutrient dispersion into the environment. Long-term N-based manure application also impacts the apparent nutrient recovery (ANR) by crops and, hence, the crop quality. Our objective was to monitor changes in soil quality and to measure nutrient recovery from N-based organic fertilization in a Brazilian agroecosystem. A long-term experiment was established in May 2004 on Typic Hapludalf soil in Southern Brazil. The experiment comprised two periods: 2004–2009 and 2009–2020. The treatments were unfertilized (control), pig slurry, pig deep litter (swine manure and rice husk), cattle slurry, and mineral fertilizer (urea, triple superphosphate, and K chloride). Grain and cover crops were grown. The maize grain yield and oat biomass were used as indicators of productivity. The application of cattle slurry, pig deep litter, and pig slurry increased the grain production by 20% on average compared to mineral fertilization. Organic manuring increased the soil pH by up to one unit, while urea acidified the soil. The highest crop yields were obtained with pig deep litter, which increased the levels of P, K, Ca, Mg, and C in the soil test. Pig deep litter showed the highest N-ANR for the aboveground part of the plants. The ANRs for P, K, Ca, and Mg were also highest when pig slurry had been applied. The ANR values for the micronutrients varied widely among the organic sources but indicated large marginal offtake gains compared to mineral fertilization. The N-based fertilization with animal manures increased the rate of nutrient uptake by plants but led to an accumulation of nutrients in the soil, threatening the sustainability of the system. Manure applications must be monitored regularly to avoid the accumulation of nutrients that could impair the soil quality and become an environmental problem in the future.

Isolation and biocontrol efficacy of entomopathogenic nematodes Steinernema carpocapsae, Steinernema monticolum and Rhabditis blumi on lepidopteran pest Spodoptera litura

Entomopathogenic nematodes (EPN) are an important component of biological control of agricultural pests. Depending on the ambient temperature, EPNs efficacy may be affected by high temperature between 30 and 40°C is usually featured in tropical and subtropical regions. In the present study, we isolated three EPN strains, namely GNAF1, NBS1 and MAF2, exhibiting high virulence on Spodoptera litura larvae and tested their lepidopteran larval control efficacy at temperatures ranging from 20 °C to 40 °C. Results show that larval control efficacy of the isolated nematodes was not affected at higher temperatures, higher emergence of infective juveniles was observed at higher temperatures, showing that EPN multiplication is not affected at higher temperatures. Based on 18s rDNA sequence these strains were identified as Steinernema carpocapsae -MK350941; Steinernema monticolum -MK503674; Rhabditis blumi -MN453373. The present study shows that these EPN can be used for controlling lepidopteran insect pest in tropical and subtropical agroecosystems.

Crop heterogeneity is positively associated with beneficial insect diversity in subtropical farmlands

Abstract Increasing crop configurational heterogeneity—smaller crop fields with more field margins—has been repeatedly found to support farmland biodiversity. But research on compositional crop heterogeneity—the number and evenness of crop types—has usually shown only weak effects. However, much of this research has been conducted in large‐scale temperate agroecosystems. We examined smallholder subtropical agroecosystems in southern China to assess the effects of crop heterogeneity on beneficial insect biodiversity. In addition to pollinators (bees, apoid and vespid wasps, and butterflies), we studied dung beetles and dragonflies/damselflies, which are not usually considered in cropland heterogeneity studies, but are abundant in these multi‐functional agroecosystems. We sampled these taxa in 468 transects placed inside 52 farms across three seasons (summer, spring and winter), collecting data on 27,245 insects belonging to 160 species. We found a strong positive effect of crop compositional heterogeneity (measured by Shannon–Wiener index) on dung beetle and dragonfly/damselfly diversity. Bee/wasp and butterfly diversity, conversely, was positively affected by crop configurational heterogeneity (measured by cumulative field margin length). Field margin type, categorized by the structure of the dominant crop types, was consistently an important explanatory variable, with weedy margins having high insect diversity. The presence of a vegetable crop on one side of the field margin, compared to non‐vegetable monocultures on both sides, increased diversity in 3/4 taxon‐season comparisons made for rice and 6/9 comparisons made for sugarcane or corn. Synthesis and applications. We demonstrate that crop compositional heterogeneity can support insects that respond to differences among crop types, including taxa that play a key role in nutrient cycling (dung beetles) and natural pest control (dragonflies/damselflies). Incorporating structurally diverse crops into monoculture Asian agroecosystems can reduce the adverse effects these intensive systems have on beneficial insects, and increase crucial ecosystem services.

Meta-analysis of yield and nitrous oxide outcomes for nitrogen management in agriculture.

Improved nitrogen (N) use is key to future food security and environmental sustainability. While many regions still experience N shortages, agriculture is the leading global emitter of N2O due to losses exacerbated by N surpluses in other regions. In order to sustainably maintain or increase food production, farmers and their advisors need a comprehensive and actionable understanding of how nutrient management affects both yield and N2O emissions, particularly in tropical and subtropical agroecosystems. We performed a meta‐analysis to determine the effect of N management and other factors on N2O emissions, plant N uptake, and yield. Our analysis demonstrates that performance indicators—partial N balance and partial factor productivity—predicted N2O emissions as well as or better than N rate. While we observed consistent production and environmental benefits with enhanced‐efficiency fertilizers, we noted potential trade‐offs between yield and N2O emissions for fertilizer placement. Furthermore, we observed confounding effects due to management dynamics that co‐vary with nutrient application practices, thus challenging the interpretation of the effect of specific practices such as fertilization frequency. Therefore, rather than providing universally prescriptive management for N2O emission reduction, our evidence supports mitigation strategies based upon tailored nutrient management approaches that keep N balances within safe limits, so as to minimize N2O emissions while still achieving high crop yields. The limited evidence available suggests that these relationships hold for temperate, tropical, and subtropical regions, but given the potential for expansion of N use in crop production, further N2O data collection should be prioritized in under‐represented regions such as Sub‐Saharan Africa.

Modelling of N2O emissions from a maize crop after the application of enhanced-efficiency nitrogen fertilisers

ABSTRACT Emission of nitrous oxide (N2O) can be reduced using enhanced efficiency nitrogen fertilizers (EEFs), such as urease inhibitors and coating technologies. In this study, we evaluated the potential of EEFs to reduce N2O emissions in maize in a clayey Inceptisol subjected to no-till management under summer subtropical conditions, in southern Brazil. The EEF sources used included urea containing N-(n-butyl) thiophosphoric triamide (UR-NBPT), polymer-coated urea (UR-pol), in addition common urea (UR), nitrate (CN) and control treatment without the application of nitrogen fertilizer. N2O emissions were assessed using the static chamber method during one maize season and analyzed through non-linear regression, using a logistic model. The accumulated emission was 0.817, 0.613, 0.457 and 0.393 kg N2O ha−1, for CN, UR, UR-pol and UR-NBPT, respectively. The maximum daily emission of N2O did not vary between amidic forms, however for CN it occurred on the 4th day after application (DAA), while for urea forms it occurred on average at 5.3 DAA. The average N2O emission factor (FE-N2O) was 0.51%, approximately half the standard factor proposed by the Intergovernmental Panel on Climate Change (IPCC), which is 1%. The application of nitrogen increased the maize yield in relation to the control, but the sources of nitrogen did not differ, with an average yield of 10,455 kg ha−1. Based on our findings, the use of UR-NBPT and UR-pol in subtropical agroecosystems provides environmental benefits, by reducing N2O emissions in comparison with conventional nitrogen fertilizers (CN and UR), however, the EEFs did not offer agronomic advantages in maize yield.

Cereal stem borer (Lepidoptera) assemblage structure in a sub-tropical agro-ecosystem, Eastern Cape Province, South Africa

Insect pests, especially lepidopterous stem borers, cause significant losses to cereal production at local and global scales. The borer species associated with cultivated grain cereals and alternative wild host plants were identified at three elevation gradients in the former Transkei area of the Eastern Cape Province, South Africa. Stem borer sampling was undertaken during maize crop and non-crop seasons in Port St Johns (PSJ), Mthatha and Elliot, sites that differ in elevation above sea level, annual precipitation and temperature. Morphologically identical borers retrieved from each sampling unit were recorded, processed and reared to adult stage for identification at an ambient temperature range of 25–28°C and a relative humidity range of 65–80%. Specimens were sorted first into morphospecies (MS1–MS6) based on external morphological characteristics. Six stem borer species (Busseola fusca, Sesamia calamistis, Eldana saccharina, Chilo orichalcocili, Chilo sacchariphagus and Chilo partellus) were collected during the survey. E. saccharina and C. orichalcocili were absent in PSJ; in Elliot, E. saccahrina occurred in very low numbers whereas C. partellus was absent. Busseola fusca was more abundant at high altitude (i.e. Elliot). Borer community structure in the study showed similarity between Mthatha and Elliot. Species richness and abundance across study sites were not statistically significant (P > 0.05). The study provides information on borer species occurrence in the study area, and techniques to identify larval stages for effective control by local farmers and extension workers. When designing strategies for borer control, elevation may not be a major concern at this spatial scale.

Pasture management, grazing, and fire interact to determine wetland provisioning in a subtropical agroecosystem

AbstractWetlands in agroecosystems provide multiple ecosystem services, including provisioning services such as forage production. Here, we examine how pasture management intensity (semi‐natural pastures vs. highly managed pastures (fertilized, heavily drained, planted with productive grasses), cattle exclusion (grazed vs. fenced), prescribed fire (burned vs. unburned), and their interactions affect provisioning services provided by small, isolated, and seasonally flooded wetlands in subtropical pastures and rangelands. We used a replicated, full‐factorial experiment on 40 seasonally flooded wetlands located in Florida (USA), and measured standing plant biomass and annual net primary productivity in each wetland. Biomass was sorted by species to calculate species abundance of palatable and unpalatable plants. We used general linear mixed models to evaluate the effect of treatments and their interactions on biomass quantity, plant tissue nutrients (% C, % N, and % P), and forage nutritive value (using in vitro organic matter digestibility). Plant standing biomass and productivity were greatest in wetlands embedded in highly managed pastures, but in grazed wetlands, a large proportion of this biomass was unpalatable to cattle. Excluding cattle from wetlands in highly managed pastures increased productivity, standing biomass, and the amount of palatable species (~6.3 t/ha) compared to grazed wetlands (~3.3 t/ha), especially when these wetlands were also exposed to prescribed fire. Total P in plant tissue was consistently higher in wetlands within highly managed pastures, but total N responses to treatments varied between years. In vitro digestibility was higher in vegetation from wetlands within highly managed pastures, but not in fenced wetlands despite the higher amount of palatable species, suggesting that palatability and digestibility were decoupled. Subtropical wetlands in agroecosystems provide substantial provisioning services, and our study suggests that targeted management can increase these services. However, the pasture type surrounding a wetland interacts with grazing and fire management to affect provisioning services. We propose that fencing off selected wetlands (specifically in highly managed pastures) followed by low‐intensity grazing with adequate resting periods could benefit ranchers and have less persistent impacts on this ecosystem.

Influence of plants on soil mites (Acari, Oribatida) in gardens

Influence of plants on soil mites (Acari, Oribatida) in gardens

Breeding Alfalfa (Medicago sativa L.) Adapted to Subtropical Agroecosystems

Alfalfa is planted in more than 30 million hectares worldwide, but despite its popularity in temperate regions, it is not widely grown in subtropical agroecosystems. It is critical to improve alfalfa for such regions, considering current predictions of global warming and the increasing demands for animal-based products. In this study, we examined the diversity present in subtropical alfalfa germplasm and reported genetic parameters for forage production. An initial screening was performed from 2014 to 2016, evaluating 121 populations from different subtropical origins. Then, a breeding population was created by crossing selected plants, resulting in 145 full-sib and 36 half-sib families, which were planted in a row-column design with augmented representation of three controls (‘Bulldog805′, ‘FL99′ and ‘UF2015′). Dry matter yield (DMY), canopy height (AH), and percentage blooming (BLOOM) were measured across several harvests. Moderate narrow-sense heritability and high genetic correlations between consecutive harvests were estimated for all traits. The breeding line UF2015 produced higher DMY than FL99 and Bulldog805, and it could be a candidate cultivar release. Several families produced higher DMY than all checks, and they can be utilized to develop high yielding and adapted alfalfa cultivars for subtropical agroecosystems.

Enhanced‐efficiency nitrogen fertilizers reduce winter losses of nitrous oxide, but not of ammonia, from no‐till soil in a subtropical agroecosystem

AbstractNitrogen (N) gas losses can be reduced by using enhanced‐efficiency N (EEN) fertilizers such as urease inhibitors and coating technologies. In this work, we assessed the potential of EEN fertilizers to reduce winter losses of nitrous oxide (N2O‐N) and ammonia (NH3‐N) from a subtropical field experiment on a clayey Inceptisol under no‐till in Southern Brazil. The EEN sources used included urea containing N‐(n‐butyl) thiophosphoric triamide (UR+NBPT), polymer‐coated urea (P‐CU) and copper‐and‐boron‐coated urea (CuB‐CU) in addition to common urea (UR) and a control treatment without N fertilizer application. N2O‐N and NH3‐N losses were assessed by using the static chamber method and semi‐open static collectors, respectively. Both N2O‐N and NH3‐N exhibited two large peaks with an intervening period of low soil moisture and air temperature. Although the short‐term effect was limited to the first few days after application, UR + NBPT urea decreased soil N2O‐N emissions by 38% relative to UR. In contrast, urease inhibitor technology had no effect on NH3‐N volatilization. Both coating technologies (CuB‐CU and P‐CU) were ineffective in reducing N losses via N2O production or NH3 volatilization. The N2O emission factor (% N applied released as N2O) was unaffected by all N sources and amounted to only 0.48% of N applied—roughly one‐half the default factor of IPCC Tier 1 (1%). Based on our findings, using NBPT‐treated urea in the cold winter season in subtropical agroecosystems provides environmental benefits in the form of reduced soil N2O emissions; however, fertilizer coating technologies provide no agronomic (NH3) or environmental (N2O) advantages.

Crop-litter type determines the structure and function of litter-decomposing microbial communities under acid rain conditions

Acid rain has been one of the major environmental problems in industrial countries. While it may affect the litter decomposition, a highly important microbial-driven biogeochemical process, knowledge about the impact of acid rain on litter-decomposing microbial communities and their functions remains unclear. Therefore, this experiment was conducted to investigate how acid rain treatments would alter microbial communities and their functions during litter decomposition of three major commodity crops (maize, rice, and soybean) for six months from June to December 2018. We used litterbag method to determine litter decomposition,while the phospholipid fatty acid (PLFA) and fluorometric methods were used to reveal changes in the litter-adhering microbial community parameters and activities of enzymes involved in the litter decomposition and nutrient release (including carbon [C], nitrogen [N], and phosphorus [P]), respectively. Our results showed that microbial community composition and functions were significantly different among litter types, but not significantly altered by acid rain treatments during the experimental period. The enzyme activities significantly correlated with each other, thus suggesting that microbial requirements for C, N, and P were coupled together during litter decomposition. Moreover, the enzyme activities, at large, did not correlate to microbial community composition, thus indicating the asymmetric relationship between microbial community structure and functions. Our results imply that crop litter type and substrate availability determined the microbial community composition and functions, while litter-inhabiting microbial communities demonstrated substantial resilience under acid rain pressure throughout the experimental period. These results also predict that litter (crop residues) decomposition may not be altered by acid rains in the subtropical agroecosystem, due to relatively high resilience of litter-decomposing microbial communities.

Life-form and Biological Spectrum of sub-tropical forests and agroecosystems of Manipur in North-east India

Life-form and Biological Spectrum of sub-tropical forests and agroecosystems of Manipur in North-east India

Plant begomoviruses subvert ubiquitination to suppress plant defenses against insect vectors

Most plant viruses are vectored by insects and the interactions of virus-plant-vector have important ecological and evolutionary implications. Insect vectors often perform better on virus-infected plants. This indirect mutualism between plant viruses and insect vectors promotes the spread of virus and has significant agronomical effects. However, few studies have investigated how plant viruses manipulate plant defenses and promote vector performance. Begomoviruses are a prominent group of plant viruses in tropical and sub-tropical agro-ecosystems and are transmitted by whiteflies. Working with the whitefly Bemisia tabaci, begomoviruses and tobacco, we revealed that C2 protein of begomoviruses lacking DNA satellites was responsible for the suppression of plant defenses against whitefly vectors. We found that infection of plants by tomato yellow leaf curl virus (TYLCV), one of the most devastating begomoviruses worldwide, promoted the survival and reproduction of whitefly vectors. TYLCV C2 protein suppressed plant defenses by interacting with plant ubiquitin. This interaction compromised the degradation of JAZ1 protein, thus inhibiting jasmonic acid defense and the expression of MYC2-regulated terpene synthase genes. We further demonstrated that function of C2 protein among begomoviruses not associated with satellites is well conserved and ubiquitination is an evolutionarily conserved target of begomoviruses for the suppression of plant resistance to whitefly vectors. Taken together, these results demonstrate that ubiquitination inhibition by begomovirus C2 protein might be a general mechanism in begomovirus, whitefly and plant interactions.

An integrated approach in subtropical agro-ecosystems: Active biomonitoring, environmental contaminants, bioaccumulation, and multiple biomarkers in fish

Aquatic contamination in agricultural areas is a global problem, characterized by a complex mixture of organic and inorganic pollutants whose effects on biota are unpredictable and poorly investigated. In this context, in the present study, the Neotropical fish Prochilodus lineatus was confined in situ for 120 days in two sites with different levels of anthropic impact: 1) a fish hatchery station, within the State University of Londrina (reference site - REF) and 2) an agro-ecosystem area in one of the most productive regions of southern Brazil (experimental site - EXP). We evaluated multiple biomarkers at different levels of biological organization, such as biotransformation and antioxidant enzymes, oxidative damages, DNA damages and liver histopathology. We also evaluated the occurrence of 22 organochlorine pesticides (OCPs) and 6 trace metals in water and sediment; and 33 current-use pesticides (CUPs) in the water; besides the presence of OCPs in the liver and metals in different tissues of the confined fish. The chemical analysis confirmed that the two environments presented different levels of contamination. We verified a distribution gradient of data in the principal component analysis (PCA), separating the REF fish to one side and the fish at the agricultural area (EXP) to the other side. In general, the biomarker responses were more altered in fish from the EXP than fish from the hatchery station; and this fish presented a greater accumulation of endosulfan (an increase of 18× compared to basal value) and showed oxidative, genetic, and histological damage. Through the Biomarkers Response Index (BRI), we found that the EXP fish demonstrated a decrease in health status compared with the REF fish during the confinement time, due to their exposure to a higher concentration of contaminants. In conclusion, the use of multiple biomarkers at different response levels is an important tool for environmental monitoring.