Shorter Fallow Periods Research Articles

Species Investigation of Rice Stem Borers and Its Parasitoids on Fallowing Rice Fields at Karawang, Indonesia

<p>Rice stem borers (RSB) cause the same damage symptoms and occur through the season and time. During the off-season for rice, these stem borers are not well-known. The research aims to determine the effect of fallowing rice on the presence of rice stem borers and their parasitoids, the potential for RSB infestation, and their parasitoid on subsequent rice seedlings in nurseries at Karawang Regency, West Java. Several variables are observed, including the number of rice stem borer larvae on stubbles, egg masses, the percentage of parasitized eggs, and the number of adults of rice stem borer in nurseries. The results show that species of rice stem borer on the fallow rice are <em>Scirpophaga incertulas</em> and <em>Sesamia inferens</em>. The population of <em>S. incertulas</em> is significantly higher on long rice fallow. The height of the paddy stubble at the two locations is not very different. However, the infested stubble in the short fallow period is higher than those in the long fallow. Eggs of <em>S. incertulas</em> whose high percentage hatched and parasitized, are primarily found in nurseries of areas with long fallow. There are three species of parasitoids identified.</p>

Shifting cultivation in decline: An analysis of soil fertility and weed pressure in intensified cropping systems in Eastern Amazon

Reconciling forest preservation and agricultural production is a major challenge. In Brazil, environmental laws have been introduced to reduce forest degradation associated with the expansion of agriculture. However, these laws are constraining small-scale family farmers who rely on cassava produced in shifting cultivation. Faced by scarcity of land, farmers are reducing the fallow periods on their farms. In this study, our hypothesis was that the reduction of the fallow period in shifting cultivation systems leads to a depletion of soil fertility and an increase in weed pressure. In the Brazilian Eastern Amazon region, soil fertility and weed infestation indicators were assessed in 36 cassava fields under shifting cultivation with different land-use histories. The frequency of cultivation of the fields in the past 10 years ranged from 1 to 7 and averaged 3.7 ± 2.3. The results show that the most frequently cultivated fields had lower soil fertility, indicated by lower soil organic carbon, total nitrogen and exchangeable potassium and pH. In addition, labor input for weeding and weeding frequency increased with the frequency of cultivation of the fields, indicating that weed pressure increased with intensified crop cultivation and shorter fallow periods. The findings of this study make clear that the current trend of reducing the fallow period in the Eastern Amazon is a threat to the sustainability and productivity of the local shifting cultivation systems. There is an urgent need for alternative production systems that allow for a better weed control and that contribute to restoring and maintaining soil fertility.

Contrasting patterns of land-cover change between early and late successional forests in a tropical montane cloud forest area managed under the milpa system

Land cover dynamics (LCD) in areas affected by different management types are hard to predict. Such is the case of tropical montane cloud forest (TMCF) areas in Mexico. The millenary itinerant milpa involves local cyclical deforestation and natural reforestation dynamics with long-lasting fallow periods. Conversely, induced grasslands for cattle, non-traditional maize cultivation with short fallow periods, and sedentary agriculture involve persistent deforestation rates. Also, human density changes could alter LCD. Ignoring such factors may lead to equivocal conclusions. We analyzed LCD using remote sensing analyses with LANDSAT images during two periods (1993–2005, 2005–2014) in a TMCF area in Sierra Norte, Oaxaca, affected by milpas, sedentary agriculture, and grasslands. We divided the study area into six indigenous sub-regions with different human population growth rates (HPG). We identified five land-cover types: mature forests (MF) dominated by TMCF species, early successional pine forests (PF), shrubby fallows (SH), croplands (milpas and more sedentary maize croplands together), and grasslands. We show that: (a) The 1993–2005 period was more variable than the 2005–2014 period, 27 % vs. 21 % of the total area displayed transitions into another class. (b) MF area dominated (277,128 ha), increased from 1993 (64.0 %) to 2014 (67.6 %), and was not statistically associated with HPG. (c) PFs decreased from 27 % in 1993 to 15 % in 2014, and their rate of change was negatively associated with HPG. (d) The total forest area (MF + PF) decreased by 9.3 %. (f) Grasslands, SHs, and croplands fluctuated between periods and sub-regions, but none exceeded 7 % of the total area. (g) Grasslands showed the greatest increase rate, mainly at the expense of forestlands. (h) The grassland and SH increments were positively associated with HPG. The heterogeneity in LCD among periods and sub-regions reveals the relevance of considering temporal and spatial scales within the same region. The persistence of MF and the PF decrease can be ascribed to the disruption of the successional dynamics related to the decline of the traditional milpa enforced by federal and state policies at the beginning of the 21st century, the sedentarization of agriculture, local conservation areas, increases of induced pastures, and human emigration. Although Sierra Norte is an essential reservoir of TMCFs, the decline of the total forest area, particularly secondary forests, is of concern given their roles in resilience and as carbon, culture, and biodiversity reservoirs. Humid mid-elevation areas of Sierra Norte are one of the few examples of mature forest persistence and secondary forest decline.

How to Improve the Benefits of Short-Term Fallow on Soil Physicochemical and Microbial Properties: A Case Study from the Yellow River Delta

Fallowing is regarded as an effective method for the self-recovery management of farmland and is generally used in cultivated land management. Studies have shown that long-term fallow has many ecological and environmental benefits. However, the long-term fallowing of farmland has also caused a decline in the grain production of farmland for a period of time. Short-term fallow can reduce the risk of food insecurity, but there are few studies on short-term fallow, especially on the comparation of different fallowing management methods and their relationship with soil microbial ecology. Our study has focused on seven treatments. Firstly, the traditional farming method was set as the control group. Native vegetation and crop-pasture vegetation were set as the fallowing vegetation. There were three irrigation–fertilization levels for each vegetation. The effects of the sampling times showed that the impact of fallow management on the soil properties became gradually stronger with time. The interactions between the sampling times and treatments showed a significant impact on organic carbon and total nitrogen. There was a significant impact of fallow management on the inorganic carbon accumulation and ammonia nitrogen consumption. Microbial biomass carbon was significantly increased by fallowing. Fallowing with irrigation could enhance the soil microbial nitrogen transformation. Some genera associated with assisting diseases were significantly increased by the native vegetation fallow and grass fallow with farmyard manure. The fallow with native vegetation showed more advantageous ecological benefits than the crop-pasture vegetation fallow. Although the crop-pasture vegetation followed the principle of ecological intensification, it failed to show better ecological benefits in the short fallow period. In irrigation management, the benefits of native vegetation and crop-pasture vegetation are similar. However, considering the lower cost of crop-pasture vegetation, crop-pasture vegetation fallow with irrigation could be a better choice. If it is difficult to implement conservation measures during the fallowing process, native vegetation fallowing without management may be the only fallowing choice.

Plant Mitochondrial-Targeted Gene Delivery by Peptide/DNA Micelles Quantitatively Surface-Modified with Mitochondrial Targeting and Membrane-Penetrating Peptides.

Plant mitochondria play essential roles in metabolism and respiration. Recently, there has been growing interest in mitochondrial transformation for developing crops with commercially valuable traits, such as resistance to environmental stress and shorter fallow periods. Mitochondrial targeting and cell membrane penetration functions are crucial for improving the gene delivery efficiency of mitochondrial transformation. Here, we developed a peptide-based carrier, referred to as Cytcox/KAibA-Mic, that contains multifunctional peptides for efficient transfection into plant mitochondria. We quantified the mitochondrial targeting and cell membrane-penetrating peptide modification rates to control their functions. The modification rates were easily determined from high-performance liquid chromatography chromatograms. Additionally, the gene carrier size remained constant even when the mitochondrial targeting peptide modification rate was altered. Using this gene carrier, we can quantitatively investigate the relationships between various peptide modifications and transfection efficiency and optimize the gene carrier conditions for mitochondrial transfection.

Yield Response of Hybrid and Open Pollinated Maize (Zea mays L.) Varieties to Different Levels of Fertilizer Nitrogen under Rain-Fed Conditions in the Bono Region of Ghana

Background. The experiment was undertaken at Nsapor, a suburb of Berekum municipality in the Bono Region of Ghana, from March 2019 to November 2019 to determine the suitable rate of fertilizer nitrogen application to optimize seed yield and yield attributes of Pannar 12 and Omankwa maize varieties in a semi deciduous agroecology of Ghana. Soil fertility is low in Ghana because of factors such as rampant annual bushfires, short fallow periods as a result of high human populations, continuous cropping, deforestation, and improper mining activities. There is also little information on crop variety and site-specific fertilizer recommendations in Ghana, resulting in inappropriate use of fertilizers by most Ghanaian farmers, culminating in low crop yields. Methods. Hybrid (Pannar 12) and open pollinated (Omankwa) maize varieties were treated with four rates of fertilizer nitrogen obtained from NPK 15-15-15 (0 kgN/ha, 90 kgN/ha, 120 kgN/ha and 150 kgN/ha) and laid out in a factorial combination in a randomized complete block design with three replicates. Results. Application of 150 kg/ha of fertilizer N to Pannar 12 variety resulted in grain yields of 6146 kg/ha and 6095 kg/ha in the major and minor rainy seasons, respectively. The results also showed that application of 120 kg/ha of fertilizer N to Omankwa variety gave grain yields of 4635 kg/ha and 5286 kg/ha in the major and minor rainy seasons, respectively. To optimize the grain yield of maize, farmers could use NPK 15-15-15 fertilizer as a source of nitrogen and apply 120 kgN/ha to Omankwa variety and 150 kgN/ha to Pannar 12 variety in both major and minor rainy seasons.

Farmers' perceptions on tomato early blight, fungicide use factors and awareness of fungicide resistance: Insights from a field survey in Kenya.

Early blight (EB) caused by Alternaria solani is one of the most devastating tomato diseases in Kenya and is most often managed by application of synthetic fungicides. However, there have been reports from farmers about the declining efficacy of some fungicides. These reports suggest that A. solani populations in Kenya could be developing resistance to some of the commonly used fungicides. In this study, we surveyed 175 tomato fields, sampled in 3 major tomato producing counties in Kenya, to determine the status of EB, management practices, and fungicide use factors that could contribute to development of resistance to fungicides among A. solani populations in Kenya. Data was recorded on farm characteristics, EB prevalence, fungicide usage, and farmers' perceptions on fungicide efficacy. EB was prevalent in 85% of the fields and 90% of the farmers identified it as a major cause of yield loss. Tomato was grown all year round on 60% of the fields with only short fallow periods. All farmers reported that they were relying on fungicides for EB control and none among the cultivars grown was resistant to the disease. A total of 40 fungicide products, representing 20 active compounds with varying FRAC resistance risk levels were in use against EB. Majority (83%) of the farmers were applying fungicides at dosages and frequencies higher than those indicated on labels. Most farmers (81%) indicated that they had observed declines in effectiveness of at least one fungicide, used at EB control. This observation was more with fungicides in the strobilurin and triazole groups. These findings demonstrate that the current tomato production systems in Kenya do not take into account the risk of A. solani developing resistance to fungicides. Enhancing farmers' knowledge of the disease and their ability to properly select and apply fungicides is therefore crucial for effective control of EB and mitigating the high risk of fungicide resistance build up.

Thinking Outside the Continent and Outside the Box: Cross-Continental Comparative Studies Can Enrich Studies of Pre-Columbian Raised-Field Agriculture

Despite an attempt at intercontinental synthesis by Denevan and Turner (1974) almost 50 years ago, studies of agricultural raised fields (RF) in the Neotropics and in Africa and New Guinea are separate research traditions, with almost no communication between them. Neotropical studies refer to “raised-field agriculture” and almost exclusively concern archaeological systems in wetlands. Studies in Africa and New Guinea refer to “mound” or “ridge” cultivation and concern mostly present-day systems (in Africa) or both present-day and archaeological systems (in New Guinea) in both uplands and wetlands. Ethnographic studies of present-day systems provide insights into questions about past systems that are inaccessible using archaeological methods alone. Our review suggests that the Neotropical focus on RF agriculture as an exclusively wetland adaptation is misleading. We argue that the most widespread purpose of building RF, in both wetland and upland environments, is to concentrate topsoil and organic matter, enabling creation of fertile patches in infertile and low-biomass grassland environments. Avoiding flooding is an important function of RF built in wetlands and wetland margins. We further show that Old World RF are often not perennial, but are short-lived structures that rotate over the landscape, being torn down and rebuilt nearby in successive cycles. Short fallow periods are allowed (or even favored) by methods of managing fertility. Finally, we argue that the restriction—on all continents—of archaeological raised fields to wetland and wetland-margin environments is, in part, a result of their better preservation from erosion in wetland than in upland environments.

‘BARI Masur‐9’: An extra‐early lentil cultivar for a rice‐based cropping system in Bangladesh

AbstractLentil (Lens culinaris Medik) is the third‐most important grain legume in the world. In Bangladesh, it is important for human food and nutrition, animal feed, and sustainable rice‐based cropping systems. However, lentil area is declining due to competition with other winter and spring crops, particularly irrigated spring rice (boro rice; Oryza sativa L.). To increase lentil production, the extra‐early (<95 d) lentil line LRIL‐22‐70 was selected to grow in the short fallow period between monsoon and spring rice under a proposed new cropping pattern. LRIL‐22‐70 was identified from a recombinant inbred line population through rigorously evaluated in diverse agro‐ecological conditions of Bangladesh and released for commercial cultivation by Pulses Research Centre, BARI, as ‘BARI Masur‐9’ (Reg. no. CV‐36, PI 700307) in 2018. BARI Masur‐9 is a transgressive segregant for earliness (matures in <93 d) and fits well in the new monsoon rice–lentil–spring rice cropping pattern. It is a medium‐seeded (2.38 g 100–1 seed) cultivar with high tolerance to Stemphylium blight. The average seed yield of BARI Masur‐9 was 1,201 kg ha–1, with higher concentrations of Fe (73 mg kg−1) and Zn (61 mg kg−1) compared with other genotypes; thus, BARI Masur‐9 contributes to combatting micronutrient malnutrition in Bangladesh. BARI Masur‐9, the first extra‐early lentil cultivar, can successfully be grown to replace fallow between rice as a new cropping pattern monsoon rice–lentil (BARI Masur‐9)–spring rice in about 8 million ha in Bangladesh, eastern Indian states, and eastern Nepal.

Crop calendar optimization for climate change adaptation in rice-based multiple cropping systems of India and Bangladesh

Adjusting crop calendars may present an effective adaptation measure to avoid crop yield loss and reduce water use in a changing climate. In order to better understand potentials and limitations of adjusting crop calendars for climate change adaptation of tropical multi-cropping systems with short fallow periods, we used a regionally calibrated Environmental Policy Integrated Climate (EPIC) agronomic model to estimate annual caloric yield and blue water requirement (BWR) of irrigated double-rice and rice-wheat cropping systems in India and Bangladesh. We adjusted crop calendars by (a) single-objective optimization to maximize annual caloric yield and (b) multi-objective optimization to minimize BWR under current and future climate scenarios, focusing on climatic drivers of optimal growing seasons. While the short time intervals between harvest of kharif crops and (trans-)planting of rabi crops limit the space for planting date shift in the study area, our results indicate that crop calendar adjustment has great potential to reverse yield loss induced by temperature rise and decrease BWR by utilizing monsoon precipitation. The study indicates a trend towards earlier planting of rabi wheat to mitigate heat stress during the reproductive stage. Moreover, earlier planting of kharif rice can help to utilize monsoon precipitation, avoid cold stress of kharif rice during anthesis, and allow for early wheat sowing during the historic period. By the 2080s, the increase of heat stress in summer and the decrease of cold stress in winter seems to allow more flexibility for late rice in kharif season, but a conflict between later planting for yield improvement and earlier planting for blue water saving is expected in kharif rice on the Indo-Gangetic plain of India and Bangladesh. Therefore, the trade-off between yield improvement and irrigation water use needs to be carefully considered to promote adaptive adjustment of crop calendars under climate change.

Soil properties and microbial processes in response to land‐use change in agricultural highlands of the Central Andes

AbstractUnderstanding changes in soil functions in response to land‐use change is important for guiding agricultural practices towards sustainable soil management. We evaluated the differences in soil properties (soil organic matter, water extractable carbon (C) and nitrogen (N), microbial biomass, pHKCL and exchangeable cations) and microbial processes (respiration potential, net N mineralization, net nitrification and metabolic potential of soil bacteria), as well as the relative importance of soil properties in explaining changes in processes under three land uses (potato crops, fallow fields and eucalyptus plantations) in the agricultural highlands of the Central Andes. Soils under potato crops were characterized by the highest net N mineralization and net nitrification rates, and extractable phophorus (P), and the lowest microbial biomass P. Conversion to eucalyptus plantations led to an increase in soil organic matter, water extractable C and microbial biomass, and a decrease in extractable P and metabolic diversity of soil bacteria. Higher exchangeable aluminium (Al) indicated soil acidification under eucalyptus. Fallow practices did not lead to major changes in soil properties and microbial processes, indicating that fallow practices for up to 6 years were too short to substantially contribute to soil fertility restoration. Hot water extractable carbon (HWC) showed the best relationship with soil processes (respiration potential, net N mineralization and net nitrification). Our results highlight the necessity of alternative management practices for maintaining soil fertility under potato crops, the drastic modification of soil properties and processes under eucalyptus plantations, and the potential of HWC as a proxy for monitoring land‐use‐induced changes in soil functions related to C and N cycling.Highlights Effects of conversion from potato crops to eucalyptus and fallow on soil properties and processes were assessed. Under eucalyptus, soil respiration increased; metabolic diversity and N transformations decreased. Short fallow periods did not result in soil fertility restoration. Hot water extractable C was the best indicator of changes in soil processes.

Short-term fallow practices drive soil bacterial community changes: A case study from China

Fallowing is considered an effective self-recovery practice for farmland and is commonly applied in the management of cultivated land. Improved fallow practices may result in shorter fallow periods, but few studies have compared the benefits of different improved fallow practices as they relate to soil microbial ecology. We established 6 fallow treatments on a continuous sorghum cropping field. Three different kinds of vegetation were planted as the fallow vegetation, and 2 levels of fertilization were applied to each vegetation type. The fallow experiments were conducted over 3 years, and each plot was sampled 3 times. The bacterial community structure in the topsoil (0–20 cm) and subsoil (20–40 cm) was determined by DNA sequencing.The results showed that manure application could significantly change the bacterial community structure and assembly processes. Manure increased the abundance of plant growth-promoting rhizobacteria and bacterial communities associated with nutrient cycling. The unfertilized plots promoted bacterial communities associated with nitrogen fixation and plant residue decomposition. In terms of the effects of the different vegetation types, plant growth-promoting rhizobacteria benefited from spontaneous vegetation with manure during the fallow process, and they also benefited from maize-alfalfa vegetation with manure in the first and third years of this study. The unfertilized alfalfa-dahurian plots had positive effects on plant growth-promoting rhizobacteria starting in the second year, while fertilized fields did not exhibit increased rhizobacteria until the third year. If the fallow vegetation is maize-alfalfa and spontaneous vegetation, manure application is necessary. Therefore, farmland fallowing could be combined with animal husbandry. However, the interactions between vegetation and manure must be considered seriously.

Intensification of agriculture in southwestern Germany between the Bronze Age and Medieval period, based on archaeobotanical data from Baden-W\xfcrttemberg

A system of farming with an alternation of land use between being cultivated or left fallow as grassland (Feldgraswirtschaft) developed in southwestern Germany since the Bronze Age. It involved fallow periods, where the arable land is left without crops in order to let it recover its fertility for several years while becoming grassland. This led to regeneration of the topsoil humus, which could later be mobilized by cultivation. With later farming systems, the supply of nutrients needed for crops could also be provided by manuring, which allowed shorter fallow periods but required the production of manure. Such cultivation systems with short or even without fallow phases and with intensive manuring are known from the medieval period as one, two or three field systems of agriculture and their development was an important step towards the intensification of farming. The current study considers on-site plant macrofossil data from archaeological sites as well as the off-site pollen data from cores in Baden-Württemberg in order to recognize the main changes towards agricultural intensification through time from the Bronze Age up to medieval times. The various landscape types included in the study area also reveal their different agricultural histories of intensification. In lowlands with good soils, the intensification can be recognized earlier and more strongly than in uplands or other marginal areas. The main shift towards intensification took place in the Roman period, which is also confirmed by written sources of the time that mention manuring as well as a kind of two field system and alternation between grassland and arable land.

Cocoa agroforestry and tree diversity in relation to past land use in the Northern Ecuadorian Amazon

Shifting agriculture (SA) involving fallow intervals between crop cycles is common in tropical areas. It allows the recovery of soil fertility for subsequent crops. However, the diminishing of fallow intervals (referred here as intensification of SA) is a main cause of forest degradation. Agroforestry systems (AFSs) based on modification of mature forests may play an important role in buffering adverse environmental outcomes caused by short fallow intervals in SA. We investigated whether AFSs reverse the effect of intensification of SA in cocoa (Theobroma cacao) agrosystems and aimed to (1) characterize species diversity in cocoa agroecosystem under SA with short fallow periods; (2) predict the ecological impact of intensification of SA on floristic composition, particularly in endangered endemic species; and (3) identify whether changes in floristic composition and species diversity in agroecosystems under different fallow intervals are localized in certain strata or whether structural changes occur throughout the plant community. Our study revealed that shortened SA’s fallow periods on cocoa AFSs have drastic effects on levels of diversity. Tree species assembly decreases across cocoa agroforest established in reduced fallow periods. Also, absence of fallow intervals of SA affects tree conservation rates in AFSs by changing floristic composition. Nevertheless, the use of AFSs with complex arboreal structures under SA preserves and protects higher rates of native and endangered endemic species and delays forest degradation rates. The conservation of native species in this agricultural model may meet the requirements to reverse the cycle of land degradation and social deprivation.

Impact of topography and sedentary swidden cultivation on soils in the hilly uplands of North‐East India

AbstractA hilly catchment (4 km2) was selected to quantify the changes in physico‐chemical soil properties when traditional shifting cultivation is converted to sedentary swidden cultivation (elements of slash and burn cultivation with short fallow period), locally called bun (cropping in rows of raised beds formed from soil), in the central part of the Meghalaya Plateau. Assuming that the monsoonal climate, deep‐weathered granites, and time are relatively uniform over the small catchment, the differences in soil were compared on two contrasting landforms (flat ridges and steep slopes) and three land use types (natural deciduous forest, sedentary swidden cultivation of potatoes, and fallow land with pine forest) within each landform. In contrast to previous studies in region, soil fertility indices calculated in the present study indicated that the bun system can also improve soil quality. Soil response significantly varied at spatial scales, however, and in terms of the possibility of continuing sustainable cultivation in the future. At a local scale on flat terrain upon granites, soil under swidden cultivation had the higher fertility indices, than fallow land and natural forest, whereas steep slope cultivated soil had the lowest fertility indices, following fallow land and natural forest. Therefore, bun system can be efficient in tropical regions with gentle terrain and limited forest resources. At a regional scale, low potato yield combined with a growing food demand forces farmers to expand potato cultivation on steep slopes, the dominant landform in the Meghalaya, increasing the risk of soil degradation. Introducing agroforestry with pine trees into bun cultivation can mitigate the rates of soil degradation on steep slopes.

Yield and Nutrient Removal in Potato‐Based Conservation Agriculture Cropping Systems in the High Altitude Andean Region of Ecuador

Core Ideas Conservation agriculture practices evaluated in this study were agronomically effective, but expensive. Reduced tillage resulted in similar yields in all crops of the potato–oat/vetch–barley–faba rotation to conventional tillage. Retaining crop and cover crops residues in the field rather than for animal fodder will make the greatest contribution to soil nutrient cycling, but likely to be the least accepted conservation agriculture practice evaluated in this study by regional farmers. The Illangama region of Ecuador's highlands is typical of much of the Andean region throughout South and Central America. Steep slopes, frequent soil disturbance and the short fallow periods threaten the sustainability of soil quality and crop production in this region. We evaluated several conservation agricultural practices, including deviation ditches, crop residue retention, and reduced tillage in the context of a potato (Solanum tuberosum L.)–oat/vetch (Avena sativa L./Vicia sativa L.)–barley (Hordeum vulgare L.)–faba bean (Vicia faba L.) rotation from 2011 to 2014 on crop productivity, crop and soil nutrient concentration, and nutrient removal from the system. Crop productivity tended to be higher in plots that had deviation ditches, and where crop and cover residues were retained in the field. Reduced tillage systems had yields similar to conventional tillage systems in all crops. Retaining crop and cover crop residues in the field had the greatest impact on recycling nutrients back to the soil, but was also the most costly conservation practice that we evaluated. Overall, conservation agricultural practices showed considerable agronomic promise for cropping systems in the Illangama region of Ecuador, but will require a longer evaluation period and a comprehensive outreach plan to help gain acceptance with regional farmers. Retaining crop and cover crops residues in the field rather than for animal fodder will make the greatest contribution to soil nutrient cycling, but likely to be the least accepted conservation agriculture (CA) practice evaluated in this study.

Shifts in swidden agriculture alter the diversity of young fallows: Is the regeneration of cloud forest at stake in southern Mexico?

Abstract For centuries, the milpa shifting cultivation, a maize-bean-squash polyculture in itinerant fields has been an essential component of the landscape (MS), in tropical montane cloud forest (TMCF) areas managed by Mesoamerican indigenous communities. At present, milpas are being replaced by a maize based semi-permanent system (SP) characterized by tillage, fire suppression, application of synthetic fertilizers, and short fallow periods. The effects of this substitution on post-cultivation fallows are unknown, but may have critical consequences for biodiversity and forest regeneration. In the TMCF area of Sierra Norte, Oaxaca, Mexico, the fallowed areas resulting from both cultivation systems are intermixed across the landscape. We compared the composition, richness, and diversity of vascular plant species in 2–3-year-old MS and SP fallows in this area, and explored the possible role of the adjoining forested areas on fallow plant species richness and density. Tree and herb species composition in the fallows separated into two clusters, one belonging to MS and the other to SP. Pioneer and late-successional TMCF tree species were distinctive of MS fallows, whereas native perennial grass and forb species were distinctive of SP fallows. The composition of other life forms could not be distinguished based on cultivation system. The species richness and diversity of trees, tree seedlings, shrubs, and vines were higher in MS fallows, whereas herb species richness and diversity was similar in both fallow types. In MS and SP fallows, the tree seedling species richness increased with the proportion of adjoining forested areas that were >20 years old, but not with forests younger than that age. Tree seedling density increased with the proportion of adjoining forested areas >20 years old in SP fallows but not in MS fallows. The density of trees and shrubs were significantly higher in MS fallows than in SP fallows, whereas herb density was significantly higher in SP fallows than in MS. We concluded that the replacement of MS by SP on the one hand, reduces plant diversity in early fallows and the fallow potential for TMCF regeneration; on the other hand, increases the dependence on adjoining >20-year-old forests as propagule sources.

Spatial and temporal dynamics of shifting cultivation in the middle-Amazonas river: Expansion and intensification

Shifting cultivation is the main land-use system transforming landscapes in riverine Amazonia. Increased concentration of the human population around villages and increasing market integration during the last decades may be causing agricultural intensification. Studies have shown that agricultural intensification, i.e. higher number of swidden-fallow cycles and shorter fallow periods, reduces crop productivity of swiddens and the regrowth capacity of fallows, undermining the resilience of the shifting cultivation system as a whole. We investigated the temporal and spatial dynamics of shifting cultivation in Brazilian Amazonia to test the hypotheses that (i) agriculture has become more intensive over time, and (ii) patterns of land-use intensity are related to land accessibility and human population density. We applied a breakpoint-detection algorithm to Landsat time-series spanning three decades (1984–2015) and retrieved the temporal dynamics of shifting cultivation fields, which go through alternating phases of crop production (swidden) and secondary forest regrowth (fallow). We found that fallow-period length has decreased from 6.4 to 5.1 years on average, and that expansion over old-growth forest has slowed down over time. Shorter fallow periods and higher frequency of slash and burn cycles are practiced closer to residences and around larger villages. Our results indicate that shifting cultivation in riverine Amazonia has gone through a process of agricultural intensification in the past three decades. The resulting landscape is predominantly covered by young secondary forests (≤ 12 yrs old), and 20% of it have gone through intensive use. Reversing this trend and avoiding the negative consequences of agricultural intensification requires land use planning that accounts for the constraints of land use in riverine areas.

A retrospective assessment of the effect of fallowing on piscirickettsiosis in Chile

Piscirickettsiosis is an endemic disease of farmed salmonids in Chile, and is the main cause of infectious disease-related losses in the Chilean aquaculture industry. Inconsistent results with the use of vaccines and antimicrobials have led producers and government to search for alternative control measures. Fallowing sites between fish production cycles has been mandated by the government authority, but the effectiveness of this practice for preventing this disease has not been assessed under field conditions. We used a discrete-time survival analysis model to evaluate the effect of the duration of the fallow period on the hazard of piscirickettsiosis during the first 24weeks of the production cycle on farms between September 2009 and August 2015. We compared the hazard of piscirickettsia for production cycles on farms that did and did not report the disease immediately before fallowing in the preceding cycle. We controlled for potential confounders, including external infectious pressure from neighboring farms. Our results showed that for both Atlantic salmon and rainbow trout there was no significant difference between the hazard of SRS for farms that reported the disease in the previous cycle and the comparison group, when these farms fallowed for more than three months. Shorter fallow periods were only assessed in rainbow trout, and findings indicate that the hazard of piscirickettsiosis is higher for farms with a recent history of the disease than for farms without a recent history of the disease prior to fallowing. These results suggest that fallowing for three months may be adequate to lower the exposure of P. salmonis from one production cycle to the next; however, our study also suggests there is a high hazard of observing SRS on farms, regardless of fallowing.

Towards settled cultivation from traditional jhum-A case study in Arunachal Pradesh, India

The shifting cultivation in Arunachal Pradesh is dynamic in nature and is known as ‘Jhum’. Upland rice is the main crop grown in mixture with maize, foxtail, finger millet, beans, cassava, yam, banana, sweet potato, ginger, chillies, vegetables, etc. in such system. The single crop of rice is preferred in the second year and this continues for 2-3 years and then it is left for fertility build up through regeneration of vegetation. The period is known as ‘fallow period’. But this leads to considerable soil erosion due to heavy intense rainfall instead of increasing its fertility. The fallow period has been reduced from 10-20 years to 5-7 years. Fortunately the mindset of the jhumias of East Siang district of Arunachal Pradesh, India has been changed. They cultivate citrus, bamboo and tache (wallichia) trees in these fallow lands, which not only prevent the land from soil erosion, but also give income even from a short fallow period. This is a little shift from the traditional practice towards a sustainable practice adopted by the jhumias. The paper presents the current scenario of settled cultivation from traditional jhum in reference to East Siang district of Arunachal Pradesh.