Fallow Phase Research Articles

Can hydrologic management practices of rice fields contribute to macroinvertebrate conservation in southern Brazil wetlands?

The expansion of rice fields is one of the main human activities responsible for the decline of natural wetlands throughout the world. However, rice fields have been recognized as having considerable potential value for many aquatic species. In this sense, an important question from the point of view of biodiversity conservation is the adequacy of these agricultural wetlands as an integrated managed landscape that contributes to maintain a rich biodiversity. The two main questions of this study were: (1) Do richness, density, and composition of macroinvertebrates differ in rice fields with different management practices (flooded and dry)?; and, (2) Do richness, density and composition of macroinvertebrates change in rice fields over the rice cultivating phases? Six collections were carried out in six rice fields with different management practices after cultivation (three dry and three flooded during the fallow phase). The macroinvertebrates were sampled using a corer (7.5-cm diameter) inserted 10 cm into the substratum of the rice fields. We recorded 6,425 macroinvertebrates, comprising 71 macroinvertebrate taxa. Macroinvertebrate richness and density varied over the rice cultivating cycle. The different management practices adopted after cultivation did not influence the macroinvertebrate richness and density; however, they influenced composition. Thus, the mosaic created by the variation of flooded and dry rice fields would provide the setting for a greater number of taxa within the agricultural landscape. The difference in taxa composition between flooded and dry rice fields is an interesting result in terms of biodiversity conservation. Rice producers could maintain part of their agricultural land flooded during the fallow phase. These management practices adopted could be an important strategy for biodiversity conservation in areas where the natural wetlands were converted into rice fields.

Evaluation of the SWEEP model during high winds on the Columbia Plateau

AbstractA standalone version of the Wind Erosion Prediction System (WEPS) erosion submodel, the Single‐event Wind Erosion Evaluation Program (SWEEP), was released in 2007. A limited number of studies exist that have evaluated SWEEP in simulating soil loss subject to different tillage systems under high winds. The objective of this study was to test SWEEP under contrasting tillage systems employed during the summer fallow phase of a winter wheat–summer fallow rotation within eastern Washington. Soil and PM10 (particulate matter ≤10 µm in diameter) loss and soil and crop residue characteristics were measured in adjacent fields managed using conventional and undercutter tillage during summer fallow in 2005 and 2006. While differences in soil surface conditions resulted in measured differences in soil and PM10 loss between the tillage treatments, SWEEP failed to simulate any difference in soil or PM10 loss between conventional and undercutter tillage. In fact, the model simulated zero erosion for all high wind events observed over the two years. The reason for the lack of simulated erosion is complex owing to the number of parameters and interaction of these parameters on erosion processes. A possible reason might be overestimation of the threshold friction velocity in SWEEP since friction velocity must exceed the threshold to initiate erosion. Although many input parameters are involved in the estimation of threshold velocity, internal empirical coefficients and equations may affect the simulation. Calibration methods might be useful in adjusting the internal coefficients and empirical equations. Additionally, the lack of uncertainty analysis is an important gap in providing reliable output from this model. Published in 2009 by John Wiley & Sons, Ltd.

Windblown dust influenced by conventional and undercutter tillage within the Columbia Plateau, USA

AbstractExceedance of the US Environmental Protection Agency national ambient air quality standard for PM10 (particulate matter ≤10 µm in aerodynamic diameter) within the Columbia Plateau region of the Pacific Northwest US is largely caused by wind erosion of agricultural lands managed in a winter wheat–summer fallow rotation. Land management practices, therefore, are sought that will reduce erosion and PM10 emissions during the summer fallow phase of the rotation. Horizontal soil flux and PM10 concentrations above adjacent field plots (>2 ha), with plots subject to conventional or undercutter tillage during summer fallow, were measured using creep and saltation/suspension collectors and PM10 samplers installed at various heights above the soil surface. After wheat harvest in 2004 and 2005, the plots were either disked (conventional) or undercut with wide sweeps (undercutter) the following spring and then periodically rodweeded prior to sowing wheat in late summer. Soil erosion from the fallow plots was measured during six sampling periods over two years; erosion or PM10 loss was not observed during two periods due to the presence of a crust on the soil surface. For the remaining sampling periods, total surface soil loss from conventional and undercutter tillage ranged from 3 to 40 g m–2 and 1 to 27 g m–2 while PM10 loss from conventional and undercutter tillage ranged from 0·2 to 5·0 g m–2 and 0·1 to 3·3 g m–2, respectively. Undercutter tillage resulted in a 15% to 65% reduction in soil loss and 30% to 70% reduction in PM10 loss as compared with conventional tillage at our field sites. Therefore, based on our results at two sites over two years, undercutter tillage appears to be an effective management practice to reduce dust emissions from agricultural land subject to a winter wheat–summer fallow rotation within the Columbia Plateau. Copyright © 2009 John Wiley & Sons, Ltd.

Soil microbial biomass and mineralization of aggregate protected carbon in fallow-maize systems under conventional and no-tillage in Central Zimbabwe

Abstract Soil organic carbon has been reported to increase soil microbial activities in soils. However, very few studies have evaluated soil microbial biomass carbon (SMBC), aggregate protected carbon, and mineralizable carbon, SOC associated with sand, silt and clay and aggregate stability under fallow-maize rotation systems. The objectives of this study were to determine SMBC, aggregate protected carbon, and mineralizable carbon, SOC associated with sand, silt and clay and aggregate stability under conventional tillage (CT) and no-tillage (NT) in a fallow-maize rotation system. We hypothesized that improved fallow systems, which are fast growing leguminous trees grown during the fallow phase, had greater SMBC, aggregate protected carbon, SOC in the different soil fractions and aggregation when compared to natural fallow or continuous maize systems. Treatments studied were improved fallows of Acacia angustissima (A. Angustissima), Sesbania sesban (S. Sesbania), natural fallow and continuous maize. Samples were collected from 0–50, 50–100 and 100–200 mm depths 1 year after fallow termination in plots subjected to CT and NT. Total SOC was determined by wet combustion, SMBC by fumigation extraction, aggregate protected SOC by wet sieving and sedimentation into sand, silt and clay after 21-day incubations of intact and crushed macroaggregates of size

Biomass production, nutrient uptake and partitioning in planted Senna spectabilis , Flemingia macrophylla and Dactyladenia barteri fallow systems over three fallow/cropping cycles on Ultisol

Biomass production and nutrient uptake of all components in planted Senna spectabilis, Dactyladenia barteri and Flemingia macrophylla hedgerow fallow were determined after three two‐year fallow phases and compared to natural fallow. Total above-ground biomass production after each of three fallow phases was significantly higher in the Senna system than any other system. Total above ground biomass production in the Flemingia and the Dactyladeniai system was not different from that in natural fallow. The volunteer biomass between hedgerows was only once significantly reduced by S. spectabilis during the first fallow phase. The amount of litter did not differ between fallow systems. The biomass of S. spectabilis, F. macrophylla and D. barteri comprised 96%, 95% and 65% wood, respectively. Relative to the total system biomass, wood constituted 67% in S. spectabilis and about 20% in F. macrophylla and D. barteri systems. Except for Mg, the S. spectabilis system accumulated more nutrients in above ground biomass than any other system. The highest nutrient uptake achieved in the S. spectabilis system was 335 kg ha−1 N, 331 kg ha−1 Ca, 230 kg ha−1 K, and 39 kg ha−1 P. Relative to the S. spectabilis system, nutrient accumulation, except for Mg, was the lowest in the natural fallow control followed by the F. macrophylla and the D. barteri system. In F. macrophylla and S. spectabilis, 95% and 85% of the nutrients were accumulated in the wood. In D. barteri the nutrient distribution between leaves and wood was approximately equal. Export of wood would remove 9–16% of the nutrients accumulated in the F. macrophylla and D. barteri systems but 27–53% in the S. spectabilis system. Potential consequences of different biomass management options for crop yields and fallow re-growth are discussed.

Analysis of the sustainability within the composite swidden agroecosystem in northern Vietnam: 1. Partial nutrient balances and recovery times of upland fields

Composite swiddening is defined as an agroecosystem that integrates upland rotating crop/fallow plots and downstream permanent wet rice fields into a single household resource system. Analyses of partial N, P, K nutrient balances in upland fields were followed over a 5-year period in northern Vietnam comparing two shifting cultivation intensities (4-year rice ( Oryza sativa)-rice-cassava-cassava ( Manihot esculenta Crantz), and 2-year rice-cassava cropping cycles) and a secondary forest. Nutrient inputs by forest burning, seeds, atmospheric deposition and output by erosion, runoff, leaching, rice straw burning and off-take in crop produce were determined. Burning of a 12-year fallow plot resulted in only moderate nutrient recycling via ashes and unburned plant materials (12.5, 2.8 and 29.8 kg ha −1 of N, P, and K, respectively) but losses (off-take and atmospheric) from the field of 91, 82 and 70% of N, P, and K, respectively of nutrients contained in plant biomass. Economic yields of rice and cassava declined rapidly with successive cropping cycles. Average yearly atmospheric depositions amounted to 29, 7, and 37 kg ha −1 of total N, P, and K, respectively. Yearly runoff and erosion (7–23 Mg ha −1 year −1) were significantly higher from cropping systems than from secondary forest plots (0–3 Mg ha −1 year −1). Yearly nutrient balances in the experimental upland fields were negative for total N, P, and K during the cropping period but on average positive for N (7 kg ha −1 year −1) and P (4.1 kg ha −1 year −1) in the secondary forest. In the more intensively managed upland fields about 139, 11, and 1600 kg ha −1 of N, P, K, respectively were lost during 4 years of cropping, with less losses occurring in the 2-year cropping cycle. If nutrient losses from forest burning were also taken into account, the cumulative nutrient losses over 5 years were 247 N ha −1 and 23 kg P ha −1 in the 4-year cropping system. The main pathway of total nutrient losses was erosion during cropping cycles but runoff during fallow periods. Soil analysis confirmed declining organic matter and N contents with increasing cropping cycles and partial recovery during fallow phases. It was estimated that fallows lasting up to 37 (incl. recovery of N losses from burning) years would be needed to restore N, and up to 6 years to restore P balances. With current fallow periods being mostly substantially shorter (about 4–6 years) the negative nutrient balances and soil erosion pose a serious threat to long-term sustainability of these upland fields.

Characterizing land-use diversity in village landscapes for sustainable mountain development: a case study from Indian Himalaya

This study aimed to analyze the ecological, socio-economic and policy implications of land-use diversity in a traditional village landscape (900–1,000 m amsl.) in the Garhwal region of Indian Himalaya. The village landscape was differentiated into three major land-use types viz., forests, settled agriculture and shifting agriculture. Settled agriculture was further differentiated into four agroecosystem types viz., homegarden system (HGS), rainfed agroforestry system (RAS), rainfed crop system (RCS) and irrigated crop system (ICS), and shifting agriculture system (SAS) was differentiated into different stages of a 4-year long cropping phase and a 7-year long fallow phase, and forests into Community Forests (CF) and Reserve Forests (RF). HGS is the most productive agroecosystem, with soil organic carbon and nutrient concentrations significantly higher than all other forest/agricultural land-uses. Farmers capitalize upon crop diversity to cope with the risks and uncertainties of a monsoon climate and spatial variability in ecological factors influencing productivity. The SAS, a land-use adopted as a means of acquiring inheritable rights over larger land holdings provided in the policies during the 1890s, is less efficient in terms of land productivity than the traditional RAS and HGS but is maintained for its high labour productivity coupled with availability of high-quality fuelwood from fallow vegetation. Dominance of fodder trees in the RAS seems to derive from policies causing shortage of fodder available from forests. Cultural norms have favoured equity by allowing hiring of labour only from within the village community and income from non-timber forest products only to the weaker section of the society. Conversion of rainfed to irrigated cropping, a change facilitated by the government, improves agricultural productivity but also increases pressure on forests due to higher rates of farmyard manure input to the irrigated crops. Existing forest management systems are not effective in maintenance of a large basal area in forests together with high levels of species richness, soil fertility and resistance to invasive alien species Lantana camara. Farmers have to spend huge amount of labour and time in producing manure, managing livestock and other subsidiary farm activities. Interlinkages among agriculture, forests and rural economy suggest a need of replacing the present policies of treating agricultural development, forest conservation and economic development as independent sectors by an integrated sustainable development policy. The policy should promote technological and institutional innovations enabling parallel improvements in agricultural productivity and functions of forest ecosystems.

Groundnut/Cassava/Maize Intercrop Yields over Three Cycles of Planted Tree Fallow/Crop Rotations on Ultisol in Southern Cameroon

ABSTRACT Lack of crop yield response to planted tree fallow led to introducing a two-year fallow phase to determine if planted tree fallow can improve soil fertility and yields over a no-tree control. Three cycles of two years fallow followed by slash-and-burn land preparation and one year of groundnut/cassava/maize intercropping were conducted with Senna spectabilis, Flemingia macrophylla and Dactyladenia barteri as planted hedgerow fallows and a no-tree control on an Ultisol in southern Cameroon. The land had been continuously cropped to maize/cassava intercrop for 5 years previous to the first two-year fallow phase. Groundnut grain yields were unaffected by fallow system in 1998 and 2001 and the sum of the three cropping years. Maize grain yield was unaffected by fallow system in 1998. In 2001 and 2004 maize grain yield was highest in the S. spectabilis system. Total maize grain yield across the three cropping years was higher in the F. macrophylla and S. spectabilis systems than in the D. barteri system. Cassava root yields were in all years and the sum of the 3 years unaffected by fallow system. Cassava root (1998, 2001) and groundnut grain (2001) yields had significant spatial responses to the distance from hedgerows, with yield increases with increasing distance from hedgerows. Annual biomass production of hedgerow prunings during cropping phases ranged from zero (D. barteri) to 3.4 Mg ha−1 (S. spectabilis). During the growth of groundnut and maize, hedgerows produced < 1 Mg ha−1 in 1998, < 0.6 Mg ha in 2001 and <0.8 Mg ha at any individual pruning. Combined relative crop yields over the three cycles were lower in planted fallow than in the no-tree control. The N export with groundnut and maize grain and cassava roots, as an indicator of crude protein production was lower in the planted hedgerow fallow systems than in no-tree control. The planted fallow hedgerow system appears unsuitable to improve crop yields because the nutrient supply from prunings is low due to their low biomass production. Yet on short distances, the spatial response of cassava and groundnut indicates competition between hedgerows and crops, which was most pronounced on cassava and groundnut in the S. spectabilis system. The crop combination appears incompatible as benefits realized by the maize were outweighed by losses in groundnut.

The Epileptology of William Aldren Turner

William Aldren Turner (1864–1945), in his day Physician to the National Hospital, Queen Square, and to King’s College Hospital, London, was one of the major figures in the world of epileptology in the period between Hughlings Jackson in the latter part of the 19th century and the advent of electroencephalography in the 1930s. Although he also made contributions to knowledge in other areas of neurology, and with Grainger Stewart wrote a competent textbook on that subject, Turner’s main professional interest throughout his career seems to have been epilepsy. On the basis of a series of earlier, rather heavily statistical, personal publications dealing with various aspects of the disorder, he authored what became a well-accepted monograph entitled Epilepsy – a study of the idiopathic disorder, which appeared in 1907, and he also gave the 1910 Morison lectures in Edinburgh on the topic. His writings on epilepsy over a period of three decades consolidated knowledge rather than led to significant advances, but helped maintain interest in the disorder during a rather long fallow phase in the development of the understanding of its nature.

Weeds – friend or foe? The role of weed composition on stover nutrient recycling efficiency

In the upland soils of Northeast Thailand, most farmers can grow only one crop per year and soils are left fallow until the next crop, leading to the establishment of a native weed population. Additionally, these areas are often very sandy thus posing a high risk of nitrogen leaching during late or erratic and early rains occurring during the fallow period. Hence the objective of this study was to assess the impact of weeds and weed composition, i.e. native weed mixture, grass or legume/broadleaf dominated weed fallows over the dry season on nutrient recycling of groundnut ( Arachis hypogaea L.) stover, i.e. mineral N and microbial biomass N dynamics, 15N pre-crop residue recovery and subsequent effects on maize yield. Maize establishment was slowest ( P < 0.05) where grass and mixed weed grew during the fallow phase and maize dry weight was initially highest ( P < 0.05) in plots where no weeds were allowed to grow during the dry season. The negative effect of grass dominated weeds was due to microbial immobilization of soil mineral N in the presence of the low quality (higher C:N ratio and ADF fibre content) grass weeds. In the second maize crop there were some indications of release of immobilized microbial N. Negative effects of grass dominated weed fallows could be overcome by addition of split doses of N fertilizer. In contrast legume/broadleaf dominated weed populations led to less microbial immobilization of mineral N and resulted in faster net release of mineral N ( P < 0.05). As a consequence, maize yields in the legume/broadleaf weed treatment (5428 kg ha −1) were higher than in the grass (2899 kg ha −1), mixed weed (3120 kg ha −1) or no weed (3552 kg ha −1) fallows over two cropping cycles. 15N balance results indicated that mixed weeds retained more groundnut residue N in the soil organic pool than the treatment without weeds during the fallow phase although the effect was not significant at P < 0.05. Identifying management options that result in a dominance of broadleaf weed composition will be crucial if weeds growing during the dry season fallow period are to improve short-term nutrient recycling. Recycling grass dominated weed biomass will require judicious fertilizer amendments or incorporation well before maize planting to avoid competition for mineral N by the soil microbial biomass.

Influence of fallowing practices on soil water and precipitation storage efficiency in semiarid Aragon (NE Spain)

The use of long fallowing (16–18 months) for soil water conservation has been questioned in semiarid drylands of Central Aragon. We quantify the soil water loss, soil water storage (SWS) and precipitation storage efficiency (PSE) of long fallow under three management systems (conventional tillage; reduced tillage; no-tillage). The precipitation storage efficiency of long fallow relative to short fallow (5–6 months) was also evaluated. Over 4 experimental years (1999–2002), the soil water balance was calculated from fallow seasonal precipitation and volumetric soil water content (0–70 cm depth). During long fallowing, primary tillage implemented in conventional tillage and reduced tillage plots induced significant soil water losses from the plough layer (0–40 cm depth) for the first 24 h after tillage. However, secondary tillage appeared to have a positive effect on soil water conservation at the end of fallow. The division of long fallow into three sub-periods showed that the early phase (July to November) was the most efficient in terms of soil water storage. Both for the individual fallow phases and the entire fallow period, the precipitation storage efficiency increased when most of the seasonal effective rainfalls (≥10 mm day −1) were received in the last 2 months of each period. Long fallow precipitation storage efficiency was low (11% on average). Neither soil water storage nor precipitation storage efficiency was significantly affected by the tillage system. The average additional soil water at sowing after long fallow compared with short fallow was 20 mm. Accordingly, the average gain in precipitation storage efficiency of long fallow relative to short fallow was only 5.3%. We conclude that long fallowing might not be suitable for enhancing soil water storage in Aragon.

Population Dynamics of Microarthropods (Oribatida and Collembola) in Rainfed Paddy Field Ecosystem in Pati, Central Java

A study on population dynamics of microarthropods (oribatids and collembolans) in rainfed paddy field ecosystem inPati, Central Java was undertaken with the aim to evaluate which group of soil microarthropods that dominated in each phase of rain fed paddy field. The soil fauna was collected using a soil corer of20 cm diameter to a depth of 0-15 cm, every 30 days.In the fallow, soil fauna was sampled from 4 randomized points per plot, meanwhile in the rice field phases (dry seeded rice and transplanted rice), it was sampled from 4 randomized points in the fields and in the bunds, respectively. per plot. Soil microarthropods in each season were then extracted in a Berlese funnel extractor.During the fallow phase, the dominant soil microarthropods were Oribatida of the Acari (1200 individual m,l) andsome groups of Collembola, namely Hypogastruridae (/200 individual m:2), Entomobryidae (500 individual m,l) andIsotomidae (620 individual m,2), meanwhile Sminthuridae of Collembola did not appear in this phase. In the rice phase,however, Sminthuridae of the Collembola occurred in high numbers, i.e., 860 individual m,2 (field) and 6/0 individual m,l(bund).Regarding the population dynamics of soil microarthropods in rainfed paddy field, we can assumed that oribatids and some groups of collembolans (Hypogastruridae, Entomobryidae and Isotomidae) play an important role in improving the nutrient availability during the fallow phase. meanwhile the Sminthuridae of collembolan seemed to play such role in the rice field phase. more than the other soil microarthropods.

Soil organic matter status of Chernozem soil in North Kazakhstan: effects of summer fallow

In North Kazakhstan there is concern about the degradation of Chernozem soil and agricultural sustainability by the inclusion and frequency of summer fallows in crop rotations in terms of their influence on the changes of soil organic matter (SOM) quality and quantity. We examined five fallow-wheat ( Triticum aestivum L.) cropping systems with different frequencies of the fallow phase in Chernozem soil of North Kazakhstan; continuous wheat (CW), 6-y rotation (6R), 4-y rotation (4R), 2-y rotation (2R) and continuous fallow (CF). Soil samples were collected from the two phases of each rotation, pre- and post-fallow, and analyzed for potentially mineralizable C (PMC) and N (PMN), ‘light fraction’ organic matter (LF-OM), C (LF-C) and N (LF-N). Potentially mineralizable C was inversely proportional to the frequency of fallow and was highest in CW. Mineral N (min-N) and PMN were more responsive to rotation phase than other indices of SOM. Mineral N was higher in the post-fallow phase while PMN was higher in the pre-fallow phase. Light fraction organic matter was negatively correlated to the frequency of fallow and was higher in the pre-fallow than in the post-fallow phase in a rotation. The results suggested that the yearly input of plant residue in a less frequently fallowed system built up more PMC, whereas PMN was closely correlated to recent inputs of substrate added with plant residues. We conclude that a frequent fallow system may deplete SOM via accelerated mineralization. Also that LF-OM, PMC and PMN are more sensitive to detect subtle changes in SOM quality than total SOM. Our results may provide prediction of SOM response to fallow frequency in wheat-based rotation systems in Chernozem soils of semi-arid regions.

Nitrate-N dynamics following improved fallows and maize root development in a Zimbabwean sandy clay loam

Improved or planted fallows using fast-growing leguminous trees are capable of accumulating large amounts of N through biological N2-fixation and subsoil N capture. During the fallow phase, the cycling of nutrients is largely efficient. However, there are few estimates of the fate of added N during the cropping phase, after the 'safety net' of fallow-tree roots is removed. Nitrate-N at the end of the fallow phase, which is pre-season to the subsequent crop, was monitored in seven land use systems in successive 20-cm soil layers to 120 cm depth at Domboshawa, Zimbabwe in October 2000. Thereafter, nitrate-N dynamics was monitored during cropping phase until April 2001 at 2-week intervals in plots that had previously 2-year planted fallows of Acacia angustissima and Sesbania sesban, and in a continuous maize control. Pre-season nitrate concentrations below 60 cm soil depth were 10 kg N ha−1 layer−1. There was a flush of nitrate in the S. sesbania and A. angustissima plots with the first rains. Topsoil nitrate had increased to >29 kg N ha−1 by the time of establishing the maize crop. This increase in nitrate in the topsoil was not sustained as concentrations decreased rapidly due to leaching. Nitrate then accumulated below 40 cm, early in the season when maize root length density was still low (<0.1 cm cm−3) and inadequate to effectively intercept the nitrate. It is concluded that under light soil and high rainfall conditions, there is an inherent problem in managing nitrate originating from mineralization of organic materials as it accumulates at the beginning of the season, well ahead of peak demand by crops, and is susceptible to leaching before the crop root system develops.

Farmers' perception of the effects of earthworms on soil fertility and crop performance in southern CameroonThe 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

Summary The knowledge and perception of the effects of earthworms on soil fertility and crop growth was surveyed in a humid forest zone of southern Cameroon. A total of 215 farmers were interviewed in seven villages: two villages were near the capital Yaounde, severely deforested with a high land-use intensity, three villages were 60–100km south of Yaounde, moderately deforested with a medium land-use intensity and two villages were 130–200km south of Yaounde, mainly forested with a low land-use intensity. To assess if the fallow phase had attained sufficiently high levels of fertility, the status of the soil macrofauna was used by 42% of farmers as an indicator. The presence of earthworm casts was used by 35% of farmers to determine if the land was ready for cropping. Earthworms were not believed to have any effect on soil fertility (98.6%) and only 0.7% of farmers believed that earthworms either increased or decreased soil fertility. Across all crops, 71.6% of farmers reported that earthworms had no effect on crop yields. Any positive effects on yields were regarded as crop specific: 30.1% of farmers believed that groundnut (Arachis hypogaea) and cassava (Manihot esculentus) yields increased if earthworms were present. For maize (Zea mays) , plantain ( Musa spp.), cocoyam (Xanthosoma sagittifolium) and cacao (Theobroma cacao) , between 27.7 and 19.2% of farmers believed that earthworms created yield increases. Few respondents (mean across crops 1.8%) believed that earthworms decreased crop yields, with the greatest proportion of these relating to plantain (3.8%). The farmers' perception of earthworms' effects on cassava and groundnut yields was very dependent on the location and related to the levels of surface casting.

Farmers' perception of the effects of earthworms on soil fertility and crop performance in southern Cameroon: The 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

The knowledge and perception of the effects of earthworms on soil fertility and crop growth was surveyed in a humid forest zone of southern Cameroon. A total of 215 farmers were interviewed in seven villages: two villages were near the capital Yaounde, severely deforested with a high land-use intensity, three villages were 60–100km south of Yaounde, moderately deforested with a medium land-use intensity and two villages were 130–200km south of Yaounde, mainly forested with a low land-use intensity. To assess if the fallow phase had attained sufficiently high levels of fertility, the status of the soil macrofauna was used by 42% of farmers as an indicator. The presence of earthworm casts was used by 35% of farmers to determine if the land was ready for cropping. Earthworms were not believed to have any effect on soil fertility (98.6%) and only 0.7% of farmers believed that earthworms either increased or decreased soil fertility. Across all crops, 71.6% of farmers reported that earthworms had no effect on crop yields. Any positive effects on yields were regarded as crop specific: 30.1% of farmers believed that groundnut (Arachis hypogaea) and cassava (Manihot esculentus) yields increased if earthworms were present. For maize (Zea mays) , plantain ( Musa spp.), cocoyam (Xanthosoma sagittifolium) and cacao (Theobroma cacao) , between 27.7 and 19.2% of farmers believed that earthworms created yield increases. Few respondents (mean across crops 1.8%) believed that earthworms decreased crop yields, with the greatest proportion of these relating to plantain (3.8%). The farmers' perception of earthworms' effects on cassava and groundnut yields was very dependent on the location and related to the levels of surface casting.

Effects of residue management on earthworm surface cast production after Chromolaena odorata short fallow in the humid tropics : The 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

We aimed to quantify the relative impact of slashing, mulching, burning and cropping on surface casting by earthworms and whether effects were due to treatments per-se or to the changes in soil temperature and water content they may induce. Surface cast production was monitored during two maize cropping seasons and the subsequent fallow phase. Slashing the vegetation caused a severe decline in surface casting activity, whether or not the plot was cropped afterwards. There was a significant interaction between burning and mulching such that there was significantly lower cast production when mulch was removed by burning than when it was removed by mechanical means. Soil temperature was lower when plots were cropped and mulched but no discernible effects of treatments upon soil water content were found. No correlations were found between surface cast production and soil water content or soil temperature.

Effects of residue management on earthworm surface cast production after Chromolaena odorata short fallow in the humid tropicsThe 7th international symposium on earthworm ecology · Cardiff · Wales · 2002

Summary We aimed to quantify the relative impact of slashing, mulching, burning and cropping on surface casting by earthworms and whether effects were due to treatments per-se or to the changes in soil temperature and water content they may induce. Surface cast production was monitored during two maize cropping seasons and the subsequent fallow phase. Slashing the vegetation caused a severe decline in surface casting activity, whether or not the plot was cropped afterwards. There was a significant interaction between burning and mulching such that there was significantly lower cast production when mulch was removed by burning than when it was removed by mechanical means. Soil temperature was lower when plots were cropped and mulched but no discernible effects of treatments upon soil water content were found. No correlations were found between surface cast production and soil water content or soil temperature.

The agronomic and economic potential of tree fallows on scoured terrace benches in the humid highlands of Southwestern Uganda

Smallholder farmers in the densely populated highlands of Southwestern Uganda face major constrains because of poor soil productivity and inadequate wood supply. The wood production, soil replenishing potentials and economic returns of five improved fallow systems: Sesbania sesban, Calliandra calothyrsus, Alnus acuminata, Tephrosia vogelii, and Acanthus pubescens were compared with the traditional bush fallow and continuous cropping systems. A trial was conducted on a non-P deficient Haplorthox (USDA) or Haplic ferralsols (FAO). Starting in March 1996, the fallow phase lasted for 2 years. Crop performance after fallow was subsequently assessed for 2 years. Soil improvement due to fallow was observed only on the degraded upper two-thirds of the terraces but not on the relatively more fertile lower terrace parts. Mineral nitrogen levels increased from 9.5 mg kg −1 in the continuous cropping systems to 17.3 and 13.1 in the Sesbania and Calliandra fallows, respectively. On the upper terrace, cumulative maize yield after fallow increased significantly from 1.6 Mg ha −1 in the continuous cropping to 3.5, 4.1, 5.9 and 6.2 Mg ha −1 in the Tephrosia, Alnus, Calliandra and Sesbania fallow systems, respectively. Besides crop yield improvement, Sesbania, Calliandra and Alnus resulted in high firewood production of 27, 26, and 24 Mg ha −1, respectively. Net benefits over the whole terraces show negative annual returns under the continuous cropping system but higher net returns of USD 229, 157, and 111 in the Sesbania, Calliandra and Alnus systems, respectively. Returns to labour are also higher in the tree fallow system, trading labour above the normal wage rate. On the upper terrace part, only Sesbania, Calliandra and Alnus systems result in positive annual net benefits of USD 185, 111, and 53, respectively. Tephrosia, natural fallow and continuous cropping systems are not profitable on the heavily degraded upper terrace as they result in negative returns.

An experimental approach to Neolithic shifting cultivation

Archaeobotanical data from Late Neolithic lake-shore dwellings (4300-3500 cal B.C.) in the northern Pre-alpine lowlands are interpreted in different ways. The presence of permanent arable fields as well as arable fields with short fallow phases and shifting cultivation with slash-and-burn has been discussed. To test these hypotheses experimentally we have been conducting tests in a forest northeast of Stuttgart since 1994. The slightly south-exposed experimental area of approximately 4.5 ha on a loess soil is covered by mixed deciduous forest, is available for at least 20 years and has been divided into 34 plots of 30 × 30 m. Up to 2001, five plots were used for experiments. The normal procedure is clearing, burning the dry small timber (less than 10 cm in diameter) and then growing winter cereals (bread wheat) for one season. The yields were between 2000 and 4000 kg grains per ha. The harvest was more or less free from weeds. First attempts with summer crops gave much lower yields of about 1100 kg grains per ha. Continuous cereal growing on the same place in the following years resulted in minimal to zero yields, mainly due to vigorous weed growth. These weeds are not crop weeds, but forest perennials of clearings and forest fringes. Ploughing to remove the weeds is not possible, because of the presence of roots and tree-stumps, most of them still living. Weed regulation by hoeing, burning or cattle grazing remains to be tested. Protection of the crop from game and birds is by fences and nets, but protection from mice seems difficult. In the spectra from the pollen traps, clearing and burning are strongly indicated, but cereal growing only slightly.