Fallow Crop Research Articles

Spatio-temporal dynamics of the parasitoid, Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae) on mealybug, Phenacoccus solenopsis Tinsley in cotton based cropping systems and associated weed flora

The mealybug, Phenacoccus solenopsis Tinsley, a polyphagous pest with a wide host range is of recent occurrence on Bt cotton in all the three major cotton growing zones in India. The first perceptible appearance of the pest on cotton in Warangal district of Andhra Pradesh was noticed in Kharif 2008. P. solenopsis was recorded on several plants other than cotton which include cultivated crops and weed hosts. The mealybug population is naturally regulated by Aenasius bambawalei Hayat (Hymenoptera: Encyrtidae). This paper reports the dynamics of this key parasitoid in a spatio-temporal perspective. Monitoring of the parasitoid on P. solenopsis occurring on weed hosts found on field bunds, crop fallows, barren lands, roadsides and village backyards indicated its activity on eight weed hosts late in the cotton growing season of 2009. During the year 2010, its activity started early in the season on few weed hosts while many more supported parasitization late in the season. Parasitoid activity was higher (11.3 to 15.3%) initially on the key hosts ( Corchorus olitorius L. , Abutilon indicum L. , and Sida acuta Burm . F.) early in the season (August) which later shifted gradually to the main host (cotton) during the later part of the season. Cropping system and spatial perspective indicated that cotton fields adjacent to roadside and crop fallows supported higher parasitization during September (8.3 - 9.1%) and cotton fields adjacent to barren lands in December (13.3%). These findings have implications for the management of P. solenopsis mealybug on cotton from an agro eco-system perspective.

Adaptability of Wheat Cultivars to a Late-Planted No-Till Fallow Production System

In Washington, over fifty percent of the wheat produced under rainfed conditions receives less than 300 mm of annual precipitation. Hence, a winter wheat-summer fallow cropping system has been adopted to obtain adequate moisture for winter wheat production. Current tilled fallow systems are exposed to significant soil degradation from wind and water erosion. As a result, late-planted no-till fallow systems are being evaluated to mitigate erosion concerns. The objective of this study was to evaluate current cultivars under late-planted no-till fallow systems to identify whether current breeding schemes in tilled fallow systems could select productive cultivars in late-planted no-till fallow systems. Thirty cultivars were planted in a split-plot design with fallow type as the main plot and genotype as the sub-plot. Fallow types evaluated were a tilled fallow system and a late planted no-till fallow system. Data were collected on heading date, plant height, grain volume weight, grain yield, and grain protein content. Analysis of variance was conducted on data across locations. Results were significant for all traits except for grain protein content. The late-planted no-till fallow system headed 16 days later was 5 cm shorter, yielded 36% less, and had a grain volume weight 3% less than the tilled fallow system. The lower yield and grain volume weight potential is hypothesized to be due to the 16 day delay in heading date leading to warmer temperatures during grain fill and a shorter duration. In order to breed wheat to be highly productive under a late-planted no-till fallow system, directly selecting in this system for early spring growth and earlier heading dates will be essential.

Long‐term‐fertilization effects on soil organic carbon, physical properties, and wheat yield of a loess soil

AbstractThe large dryland area of the Loess Plateau (China) is subject of developing strategies for a sustainable crop production, e.g., by modifications of nutrient management affecting soil quality and crop productivity. A 19 y long‐term experiment was employed to evaluate the effects of fertilization regimes on soil organic C (SOC) dynamics, soil physical properties, and wheat yield. The SOC content in the top 20 cm soil layer remained unchanged over time under the unfertilized plot (CK), whereas it significantly increased under both inorganic N, P, and K fertilizers (NPK) and combined manure (M) with NPK (MNPK) treatments. After 18 y, the SOC in the MNPK and NPK treatments remained significantly higher than in the control in the top 20 cm and top 10 cm soil layers, respectively. The MNPK‐treated soil retained significant more water than CK at tension ranges from 0 to 0.25 kPa and from 8 to 33 kPa for the 0–5 cm layer. The MNPK‐treated soil also retained markedly more water than the NPK‐treated and CK soils at tensions from 0 to 0.75 kPa and more water than CK from 100 to 300 kPa for the 10–15 cm layer. There were no significant differences of saturated hydraulic conductivity between three treatments both at 0–5 and 10–15 cm depths. In contrast, the unsaturated hydraulic conductivity in the MNPK plot was lower than in the CK plot at depths of 0–5 cm and 10–15 cm. On average, wheat yields were similar under MNPK and NPK treatments and significantly higher than under the CK treatment. Thus, considering soil‐quality conservation and sustainable crop productivity, reasonably combined application of NPK and organic manure is a better nutrient‐management option in this rainfed wheat–fallow cropping system.

Development and evaluation of a new method for sampling and monitoring the symphylid population in pineapple

Symphylids (Hanseniella sp.) are polyphagous soilborne parasites. Today, symphylid populations on pineapple are monitored by observing root symptoms and the presence of symphylids at the bottom of basal leaves. The authors developed a reliable method with a bait and trap device to monitor symphylid populations in pineapple or fallow crops. The spatial distribution of the symphylid populations was evaluated using the variance/mean ratios and spatial analyses based on Moran's and Geary's indices. The method has been tested to monitor symphylid populations at different developmental stages of pineapple. Adding potato baits to the soil samples increased the trapping efficiency of symphylids when compared with 'soil only' and 'bait only' methods. The handling of the samples is also facilitated by the new device. Results showed that the vertical distribution of symphylids may be uniform deeply inside the soil profile under pineapple, up to 50 cm. Results showed that symphylid populations are highly aggregated, showing a spot area about 4-6 m wide for their development. The new method allows better and easier evaluation of symphylid populations. It may be very useful in the evaluation of new IPM methods to control symphylids under pineapple.

Effect of live hairy vetch and its incorporation on weed growth in a subtropical region

Two of the many benefits of including legume cover crops in a fallow cropping system are weed suppression and increased soil organic N. This study was conducted in order to examine the effect of hairy vetch (Vicia villosa) on weed growth and soil N through a fallow period in subtropical Okinawa, Japan. Together with an untreated control plot, hairy vetch was grown from November 2007 to April 2008 and subsequently incorporated into the soil. The weeds were allowed to develop uncontrolled for 2 months until the time when a cash crop would be planted. In the period after the incorporation of hairy vetch, the weed biomass in the hairy vetch (HV)+ plot was more than threefold greater than that in the HV− plot. Hairy vetch had a high tendency to uptake N in April before the incorporation of hairy vetch; the N uptake by the weeds was lower in the HV+ plot than in the HV− plot. After the incorporation of hairy vetch, the N uptake by the weeds in the HV+ plot was two‐to‐six times higher than that by the weeds in the HV− plot. The C/N ratios of hairy vetch and the weeds in the HV+ plot were lower than those of the weeds in the HV− plot. More than half of the hairy vetch residue and N in the residue had decomposed by 28 days after incorporation. The content of both the NH4‐N and NO3‐N in the HV+ soil was higher than that in the HV− soil. Moreover, the amount of NO3‐N increased during the growing period of hairy vetch and decreased after the incorporation of hairy vetch. The fallow soil into which hairy vetch had been incorporated displayed a greater weed biomass and resulted in a higher inorganic N content than the soil that had not supported hairy vetch.

Soil properties governing soil erosion affected by cropping systems in the U.S. Pacific Northwest

In the low-precipitation zone (<300mm annual precipitation) of the inland US Pacific Northwest, no-tillage spring cereal rotations are being examined as alternatives to the traditional winter wheat–summer fallow rotation to control wind erosion. There is limited information, however, regarding the effects of no-tillage cropping systems on soil physical properties and surface characteristics that govern wind erosion in this semiarid region. The objective of this research was to characterize soil aggregates, wetness, strength, roughness, crusting, and crop residue cover and biomass of a silt loam that had been subject to various crop rotations for 11 years in east-central Washington. Crop rotations examined included no-tillage spring barley–spring wheat (NTSB/SW), no-tillage spring wheat–chemical fallow (NTSW/CF), and winter wheat–summer fallow (WW/SF). Soil physical properties were measured in spring 2006 after sowing wheat in the NTSB/SW rotation and in late summer 2006 after sowing winter wheat in the WW/SF and NTSW/CF rotations. In spring, the NTSB/SW and NTSW/CF rotations were characterized by a wetter soil as compared with the WW/SF rotation. In late summer, the NTSB/SW rotation was characterized by a soil surface with more standing stubble and greater crust cover and soil strength as compared with the WW/SF and NTSW/CF rotations. Our results suggest that spring-sown cereal and chemical fallow cropping systems result in wetter soils in spring and retain more surface residue in the late summer that will reduce the risk for wind erosion as compared with the traditional WW/SF rotation in the Pacific Northwest.

A legume rotation crop lessens the need for nitrogen fertiliser throughout the sugarcane cropping cycle

While the amount of nitrogen (N) contributed to agricultural soils by above ground legume biomass can be over 300 kg N/ha when grain is not harvested, its availability to subsequent sugarcane crops is uncertain. In Australia it is generally accepted that inorganic N fertiliser applied to the sugarcane (Saccharum officinarum L.) crop in the first year (termed the plant crop) following a ‘good’ legume fallow crop that is not harvested can be substantially reduced, or even eliminated. However, current recommendations do not consider the carry over of legume N to crops beyond the plant crop (termed ratoons), for which standard N fertiliser rates are considered necessary. Based on a simple field experiment extending the duration of a soybean ( Glycine max L .) fallow and two sugarcane crops (plant and first ratoon), cropping system simulation was used to provide a first estimate of how long and how much soybean N remains available for uptake by sugarcane following a soybean break crop. The soybean and sugarcane rotation plot was carried out at Mossman, Queensland over 3 years during which crop yield, plant N, and total soil C and mineral N were measured. The soybean variety Leichhardt produced 9 t/ha (±0.7) above ground dry weight, containing 301 kg N/ha (±36) which contributed to the soil N stores. After independently developing parameter values for Leichhardt, model simulations were run. The model explained 91% of the variation observed in soil mineral N to a depth of 1.5 m. Additional legume and sugarcane rotation simulations were run for the Burdekin and Bundaberg sugarcane regions. Across all three study sites the simulations suggested that legume N was available to the sugarcane crop up to the fourth ratoon. Acknowledging the limitations of this initial exploratory study, it is hypothesized that potential reductions in fertiliser application rate could be up to approximately 100% in the first ratoon, and 60%, 25% and 10% in the subsequent ratoons. These findings require further validation but suggest a potential economic and environmental win–win outcome from refining N management practices in sugarcane-legume rotation cropping systems in Australia and other countries.

Combined effects of Stylosanthes guianensis fallow and tillage management on upland rice yield, weeds and soils in southern Benin

Intensifying upland rice cultivation has resulted in increased weed pressure and declining soil fertility and rice yield in West Africa. Integrated crop management technologies are needed for enhancing rice productivity. A field experiment was conducted from 2006 to 2008 in a Typic Haplustult soil in southern Benin to identify the optimal seeding date of stylo relay-cropped into upland rice, and to evaluate the effects of fallow treatment and tillage management on rice yield, weed biomass and soil properties. Stylosanthes guianensis (stylo), a legume species, was used as a short-term fallow crop. Rice was grown once each year and stylo was seeded during the wet season and grown until the next rice-growing season. The effects of fallow treatment and tillage management (no-tillage vs. manual-tillage) on weed biomass during the rice-growing season were evaluated in 2007 and 2008, whereas the effects on rice yield were examined in 2007 alone. Results indicated that stylo can be established as a relay crop with upland rice about 10 days after rice seeding. Stylo fallow reduced weed biomass by 71% and 95% and increased total biomass (weed + stylo + litter) by 594% and 107% at the end of the dry seasons in 2007 and 2008, respectively. No-tillage without stylo fallow increased weed biomass by 62–202% over manual-tillage during the rice-growing seasons, whereas stylo fallow reduced weed biomass by 45–83% and 11–36%, respectively, under no-tillage and manual-tillage management. There were no significant effects of fallow treatment and tillage management on soil organic C, total N, inorganic N and extractable P. Rice yields following stylo fallow were 0.7 Mg ha−1 higher than after the natural fallow. Manual-tillage increased rice yield by 0.6 Mg ha−1 over no-tillage. Manual-tillage combined with stylo fallow can be recommended to smallholder farmers for improving upland rice productivity.

Contributions of leguminous cover crops in yam production systems in Southeastern Nigeria: II. Soil Organic matter, NPK and yam yields

Field experiments were conducted between 2003 and 2006 at Umudike, Southeastern Nigeria, to evaluate ten legume cover crops for soil fertility improvement and yam production. There were twelve treatments and consisted of ten legume species (Mucuna pruriens utilis, Mucuna pruriens IRZ, Mucuna georgia, Mucuna veracruz, Aeschynomene histrix, Pueraria phaseoloides, Stylosanthes capitata, Chamacrista rotundifolia, Centrosema pubescens and Crotolaria ochroleuca) in comparison with natural fallow (grass cover) and natural fallow plus inorganic fertilizer NPK Mg. The experiment was a randomized complete block design with three replicates. Soil organic matter content in 2004 was significantly higher with Aeschynomene histrix than with other cover crop fallows except Pueraria phaseoloides, Crotolaria ochroleuca and Mucuna georgia. Yam tuber yields, obtained after Aeschynomene histrix fallow were significantly higher than those obtained with grass cover, inorganic fertilizer and other legume cover crop fallows except Crotolaria ochroleuca, Pueraria phaseoloides, Chamacrista rotundifolia and Mucuna pruriens IRZ.

Effect of soybean (Glycine max) as a breakcrop on the cane and sugar yield of sugarcane

The high nitrogen requirement of sugarcane is problematic for small scale farmers in Zimbabwe due to the high cost and scarcity of fertilizer. Producing legume crops in rotation with sugarcane during the fallow period may alleviate the problem. The main aim of this research was to establish whether vegetable and grain soybeans used as fallow crops in sugarcane will benefit small scale farmers. Experimental design was a split-plot design with main treatments 1) vegetable soybean used as a fallow crop, 2) grain soybean used as a fallow crop and 3) fallow treatment (control) where the land was fallowed. After the fallow period sugarcane variety CP72-2086 was planted and topdressed with either 80 kg N ha−1 or 120 kg N ha−1 as the subplot treatments. Leaf area index (LAI), leaf nitrogen content (N content), sugarcane and sugar yield were measured. Cane planted in vegetable soybean plots and topdressed with 80 kg N ha−1 produced significantly higher cane and sugar yields compared to cane grown on fallow plots that received 120 kg N ha−1. Incorporating vegetable soybeans in the system can therefore save about 40 kg N ha−1 while increasing cane yield resulting in a more profitable cane production cycle.

Growth responses of the perennial legume Sesbania sesban to NH 4 and NO 3 nutrition and effects on root nodulation

Preference for NH 4 + or NO 3 − nutrition by the perennial legume Sesbania sesban (L.) Merr. was assessed by supplying plants with NH 4 + and NO 3 − alone or mixed at equal concentrations (0.5 mM) in hydroponic culture. In addition, growth responses of S. sesban to NH 4 + and NO 3 − nutrition and the effects on root nodulation and nutrient and mineral composition of the plant tissues were evaluated in a hydroponic setup at a range of external concentration of NH 4 + and NO 3 − (0, 0.1, 0.2, 0.5, 2 and 5 mM). Seedlings of S. sesban grew equally well when supplied with either NH 4 + or NO 3 − alone or mixed and had high relative growth rates (RGRs) ranging between 0.19 and 0.21 d −1. When larger plants of S. sesban were supplied with NH 4 + or NO 3 − alone, the RGRs and shoot elongation rates were not affected by the external concentration of inorganic N. At external N concentrations up to 0.5 mM nodulation occurred and contributed to the N nutrition through fixation of gaseous N 2 from the atmosphere. For both NH 4 + and NO 3 −-fed plants the N concentration in the plant tissues, particularly water-extractable NO 3 −, increased at high supply concentrations, and concentrations of mineral cations generally decreased. It is concluded that S. sesban can grow without an external inorganic N supply by fixing atmospheric N 2 gas via root nodules. Also, S. sesban grows well on both NH 4 + and NO 3 − as the external N source and the plant can tolerate relatively high concentrations of NH 4 +. This wide ecological amplitude concerning N nutrition makes S. sesban very useful as a N 2-fixing fallow crop in N deficient areas and also a candidate species for use in constructed wetland systems for the treatment of NH 4 + rich waters.

Nutrient Dynamics in a Long‐Term Cereal‐Based Rotation Trial in a Mediterranean Environment: Nitrogen Forms

Mediterranean agriculture is mainly rainfed, with drought being the main crop production constraint, and is based on cereals, wheat (Triticum spp), and barley (Hordeum vulgare). Fallow was a traditional practice to conserve soil moisture, but because of land‐use pressure it is giving way to cereal monoculture, which is unsustainable. The substudy reported here was part of a long‐term rotation trial that sought to examine alternative crop rotation options, that is, durum wheat (T. durum var durum) in rotation with fallow, summercrop (melon, Citrullus vulgaris), wheat (continuous cropping), chickpea (Cicer arietinum), lentil (Lens culinaris), vetch (Vicia sativa), and medic (Medicago spp). Ancillary treatments involved nitrogen (N) applied to the cereal phase and variable stubble grazing intensity (stubble retention, medium grazing, and heavy grazing or complete stubble removal). This substudy, conducted in the final 3 years of the 14‐year trial, involved sampling soil and plants within the cropped rotation plots and sampling soil within bare microplots in selected larger rotation plots. We measured N forms in soil samples at different depths and throughout the seasons. Despite variation within and between seasons, the rotation effect of enhanced N was significant and consistent, being highest for vetch and medic, intermediate for chickpea and lentil, and least for continuous cereal, summer crop, and fallow. Therefore, legume‐based cereal rotations can enhance soil N and thus save on N fertilizer. In bare microplots, total N decreased, labile N was inconsistent, mineral N increased, and biomass N increased and remained stable during the cropping season and then sharply declined. The nutrient dynamic data complemented the crop yield, water‐use efficiency, and soil aggregation data from the trial to support the argument for using legumes in cereal rotations in place of fallow and continuous cereal cropping.

Broussonetia papyrifera (paper mulberry): its growth, yield and potential as a fallow crop in slash-and-burn upland rice system of northern Laos

In northern Laos, shortened fallows in the slash-and-burn upland rice system are not sustainable either from a production or economic standpoint. This paper evaluates the potential for using the indigenous fast-growing tree, Broussonetia papyrifera L. Vent. (paper mulberry) as an economic fallow crop. The objectives of this study are to assess the inner bark yield of paper mulberry, and to evaluate rice productivity following paper mulberry cultivation. In addition, allometric models for estimating the inner bark yield of paper mulberry are developed. Inner bark yield of paper mulberry stands ranging in age from 9 to 48 months ranged from 10 to 208 g m−2, and increased with age. The models using diameter at breast height and stem height, or diameter at breast height only as independent variables explained well the variation in inner bark yield. When paper mulberry was completely removed during the rice growing season, rice yields in these areas were similar to those following weedy bush fallow. When paper mulberry was allowed to grow, rice yields were negatively correlated to paper mulberry stem density. When paper mulberry lateral branches were pruned back, rice yields could be maintained if the paper mulberry stem density was <0.22 stems m−2, suggesting that if paper mulberry is managed properly, rice yields can be maintained at current levels. The paper mulberry-upland rice rotation system improves the productivity of a traditional slash-and-burn system through harvesting paper mulberry inner bark; however the long-term sustainability of such a system remains unclear and warrants further investigation.

Impact of improved fallow periods on soil properties and productivity of maize ( Zea mays L.) in major and minor seasons of Asian humid tropics

Improved fallows are considered an easy, low cost and suitable method of increasing the productivity and sustainability of smallholder tropical rainfed cropping systems, although most farmers allow weeds to grow when the environmental conditions are not conductive for crop production. Field studies were carried out over the minor and major seasons, to evaluate the impact of a preceding improved fallow using Crotalaria or Tithonia , two popular tropical green manures, on selected soil properties, and on the growth and yield of maize. Improved fallows enhanced chemical soil properties significantly and the impact was most prominent at the onset of the minor maize season. Thus, the growth and yield of maize was also increased to a greater extent in this season, when yields are generally lower due to the suboptimal climatic conditions of lower rainfall and higher temperatures. However, fallows in the minor season also improved soil characteristics and maize yields in the major season, the most significant impact being increased seed yields and harvest indices. Although farmers may not grow fallow crops in major seasons, the potential of these green manure fallows in increasing maize yields in minor seasons and possible strategies to include the fallows in the cropping sequences of tropical rainfed upland cropping systems are discussed on the basis of this field study.

Modelling of planted legume fallows in Western Kenya. (II) Productivity and sustainability of simulated management strategies

Improved fallow is a technology that can help to raise agricultural productivity in systems of poor soil fertility and low financial capital. Models, once calibrated, can be used to investigate a range of improved fallow systems relatively quickly and at relatively low cost, helping to direct experimental research towards promising areas of interest. Six fallow crop rotations were simulated using the WaNuLCAS model in a bimodal rainfall setting in Kenya over a 10 year period: (A) alternating fallow and crop seasons, (B) one season fallow followed by three seasons crop, (C) one season fallow followed by four seasons crop, (D–F) 1–3 seasons fallow periods followed by 3–5 seasons crop. The strategies were tested using a number of fallow growth rates, soil clay contents, and rainfall amounts to determine the interaction of fallow rotation and biophysical variables on maize (Zea mays (L.)) yield and sustainability (organic matter, N2 fixation, leaching). The best simulated fallow strategies doubled maize yield compared to continuous maize over a 10 year period. Across all biophysical treatments strategy A and B of no more than three consecutive cropping seasons and of one consecutive fallow season yielded the most maize. This was because fallow benefits were largely due to the immediate fallow soil fertility benefit (IFB) rather than the cumulative benefit (CFB). The difference in yield between the two strategies was through a balance between (1) their interaction with the biophysical variables affecting accumulation of organic matter, hence increasing soil fertility and (2) the extra intrinsic soil fertility used for maize productivity by the inclusion of more cropping seasons within the rotation. We propose the following conceptual framework to manage fallows for maximum maize yield: when environmental factors are strongly limiting to fallow and crop growth then fallow strategy A would be the best strategy to employ (less risk but more labour) and when factors are less limiting then strategy B would be the best to employ.

Effects of crop and pasture rotations and surface cover on rainfall infiltration on a Kandosol in south-west Queensland

An experiment was conducted on a Kandosol in south-west Queensland from 2001 to 2005 to determine the effects of fallow management practices and crop and pasture rotations on soil properties and crop production. In April 2004, infiltration measurements were made using a rainfall simulator at the end of a 6-month fallow period following harvest of crop phases (wheat under reduced tillage and zero tillage, chickpea under zero tillage) and following termination of pasture phases (2-year legume and grass + legume leys) with herbicide application and zero tillage during the fallow period. Measurements were made at 3 surface cover levels in each treatment: (i) where crop or pasture dry matter was cut at ground level and removed to approximate 0% cover, (ii) at existing cover percentage, and (iii) where wheat straw was added to give 100% cover. In a separate study to monitor water infiltration, the movement of bromide applied to the soil surface in November 2003 was monitored in the soil profile to 1.5 m soil depth in April 2004 and February 2005. Mean cumulative infiltration after 100 mm rainfall over 1 h was 35, 42, and 69 mm (l.s.d. P = 0.05, 6) with 0%, existing, and 100% cover, respectively, and was greater following wheat (52 mm) than following chickpea (39 mm) under zero tillage (l.s.d. P = 0.05, 13). Short-term pasture leys did not appear to improve infiltration characteristics of the soil under the conditions of this study. In the rainfall simulator study, mean drainage of water below 1.5 m soil depth was 8.5% of applied rainfall. In the bromide tracer study, only ~12% of the applied bromide could be accounted for in the 0–1.5 m soil depth 15 months after application. Rainfall received during this period was similar to the long-term mean amount. Results demonstrate the importance of surface cover in increasing rainfall infiltration on this soil, thereby potentially improving soil water storage for crop and pasture production and reducing the risk of runoff and soil erosion. However, the relatively rapid movement of water and solutes through the soil profile has implications for possible adverse effects of drainage to lower parts of the landscape and for nutrient leaching below the root-zone, decreasing the availability of soil and applied nutrients to crops and pastures.

Short- and Long-term Maize Yield Response to Mucuna pruriens and Pueraria phaseoloides Relay Fallow and Biomass Burning Versus Mulching in the Forest Zone of Southern Cameroon

ABSTRACT Maize was relay cropped with the cover crops Mucuna pruriens or Pueraria phaseoloides for between one and seven consecutive years in three sites: Ngoungoumou, located in an area of low land use intensity (LUI), about 100 km away from the next major market, and at Evendissi and Andok, in a medium LUI area, 15 to 20 km away from the next major market. Maize performance was compared with that in a natural fallow system, with fallow biomass burned versus retained as mulch in both fallow types. Fallow type had no effect on maize density. After biomass burning higher maize densities were attained at the low LUI site. Maize cob production was affected neither by fallow type nor by biomass management. Across seven years of cropping, marketable cob production in the low LUI site was 38.5% higher in mucuna fallow than in natural fallow (p ⁢ 0.06). Differences at p ⁢ 0.05 were found in one out of seven years. In the medium LUI sites, mucuna and pueraria fallow increased marketable cob production by 70–132% (p ⁢ 0.001). Maize grain yield was closely related to the marketable cob production in all sites. In the low LUI site the cumulative maize grain yield over seven years was 30% higher in mucuna fallow than in natural fallow (p < 0.07), the difference being significant at p ⁢ 0.05 in only one year. In the medium LUI sites maize grain yield was 65% higher in mucuna fallow (p < 0.001) and 69–94% higher in pueraria fallow (p ⁢ 0.001). Burning biomass had a cumulative grain yield advantage of 33% at the low LUI site (p ⁢ 0.053), with significant (p ⁢⁢ 0.02) differences in two out of seven years. Biomass burning had no effects on maize grain yield in the medium LUI sites. No interactions between fallow type and biomass management were found. Despite the lack of frequent significant advantages of the cover crop fallows in the low LUI site, the system can be recommended because it has the potential to increase food diversity and security; in the medium LUI sites farmers were immediately convinced of the benefits of the system and have since moved on to grow high value vegetable crops.

Soil Hydraulic Characterisation under Different Cropping Patterns in Sloping Agricultural Lands in Sri Lanka

*** Abstract The highlands of Sri Lanka are generally considered as agriculturally productive, and yield potentials are high. However, in recent years, most agricultural lands in the hilly areas are being over-exploited, ignoring long-term negative impacts on the soils and the environment. Different forms of cropping can also modify soil conditions which can have positive or negative consequences on the soil quality. Thus, the objectives of this study were to evaluate the effects of different cropping patterns under different terrains in the Welimada Division of the upper watershed of Sri Lanka on soil quality using selected soil hydraulic characteristic indicators, and to identify which among them provides more positive effects on soil hydraulic quality for crop growth and production. The soil hydraulic characterisation conducted in the Yala (dry) and Maha (rainy) seasons in year 2004 involved measurements of infiltration, hydraulic conductivity, moisture retention characteristics, texture, and organic matter in selected zones of the Welimada watershed. Typical transects or hillslopes were selected based on varying cropping pattern and slope, and were divided into three or two field sites along the slope. A more integrated approach of assessing soil hydraulic quality based on soil hydraulic quality index was adopted to compare the hydraulic quality of soils under different cropping patterns. Analysis of the data gathered indicated that the effects of different cropping patterns are more pronounced in the rooted subsoil layer. In general, the potato-fallow-vegetable- fallow cropping rotation was identified as the pattern which provided more positive effects on the soil hydraulic quality in the context of enhancing crop growth and production. The more agriculturally intensive irrigated lowlands, particularly the paddy- potato-vegetable rotation, showed the potential of increasing the income of farmers without adversely affecting soil hydraulic quality.

Integrating environmental and sociological approaches to assess the ecology and diversity of herbaceous species in a Sudan-type savanna (Bondoukuy, western Burkina Faso)

The aim of this paper is to assess the composition and richness of the herbaceous species flora of a West African Sudan-type savanna with respect to the soil profile characteristics as well as the textural and chemical properties of the topsoil and the woody cover. The ecological profile method was used to assess the preference of species in relation to various ecological factors; we present in addition an attempt to improve the method by comparing the “ecological” and “phytosociological” affinities of each species. Species-distance matrices calculated from the ecological profiles on one hand (ecological distance between species) and from species associations on the other hand (vicinity distance between species) were chosen for comparison. A procrustean co-inertia analysis made it possible to calculate the distance between the “ecological” and “vicinity” co-ordinates of each species as a measurement of the correspondence between its ecological and sociological affinities. Thus, it was determined whether the species habitat was accurately characterised by the descriptors studied. To each of the 130 selected herbaceous species of the savanna an ordinal number was assigned as a value indicating their preference for each ecological factor studied. In addition, results showed that the floristic variability of herbaceous species is related primarily to the characteristics of the higher horizon of the soil, especially texture (clayey vs. sandy) and cation content, and only secondarily to the characteristics of the profile, in particular those which determine the internal soil drainage. However, the ecological–sociological distance is high for some species that are known to be rather ubiquitous, or characteristic of large sociological units, and also for species that are related to successional vegetation stages as well as for species that are sensitive to grazing. The herbaceous species richness is determined mainly by the degree of environmental constraints (e.g. it is low in shallow hydromorphic clayey soils on hardpan and high in wet, woody savannas) and is influenced by the sand–clay ratio of the soil. There is on the other hand, no quantitative evidence of lower species richness due to the current anthropogenic disturbance regimes resulting mainly from fallow–crop rotation and cattle herding that in fact seem to be compatible with a certain level of herbaceous species richness.

A process-based model of old field succession linking ecosystem and community ecology

This paper presents a mechanistic model of plant succession to simulate the growth of natural vegetation during long fallow periods in traditional cropping systems of the high tropical Andes. The vegetation is described as a multilayer mixture of species in competition for light and soil nitrogen. In each layer leaves are randomly distributed. The model predicts growth and biomass production of each species, and takes into account carbon and nitrogen cycling through plants and soil. It uses a daily time-step with meteorological data as forcing variables. It considers six species with four organs: leaves, stems, seeds and roots. It simulates photosynthesis; growth and maintenance respiration; carbon allocation; nitrogen uptake, fixation and remobilization; tissue mortality; and seed dispersion and germination. Our simulations show among other results that: (1) it may be difficult to detect changes in the amount of soil nitrogen during fallow periods, because simulated changes in soil nitrogen are lower than the spatial variability of the measurements; (2) how the initial seed pool and resource availability affects the pattern of succession and the dominant or co-dominant late successional species; and as a consequence (3) higher soil nitrogen availability may not always result in higher ecosystem productivity. The implication of these modeling results for the management of long fallow cropping systems is also discussed.