Fallow Season Research Articles

Analysis of seasonal change in paddy soil structure based on the elasto-plastic deformation model

Paddy soil, puddled and submerged for a few months every year, shows remarkable shrinkage when it dries, but cannot swell up to its original volume when it is submerged again. Such volumetric change induces desiccation cracks, which significantly affect the hydrological behavior of paddy fields. The present study aimed to reveal the basic behavior of cyclic shrinkage and swelling of clayey paddy soil with regard to water management during cultivation and precipitation in the fallow season. The study also aimed to examine the applicability of the elasto-plastic deformation model to the temporal changes in water retention and volume change of paddy soil. Undisturbed soil samples from a clayey experimental paddy were taken repeatedly from the top soil and hardpan layers in a rice monoculture paddy field and a rotationally cropped paddy field, both having clayey soil. Sampling was performed three times a year from July 2005 to April 2007: 1) at the end of two months of continuous flooding after puddling, 2) after drying by the release of poding water, and 3) after the wet fallow period in winter. The samples were subject to measurement of Water Retention Characteristics (WRCs) by multiple saturation and dehydration treatment in the laboratory. The samples were saturated first and dehydrated at 3.1, 10, 20, 40 and 80 kPa in a pressure chamber. They were then saturated again and dehydrated at 3.1 and 80 kPa. From the difference in the retained water at 3.1 kPa of suction between the first and second dehydration, the amount of pore volume subject to irreversible volumetric shrinkage was evaluated. The amount of water retained by puddled soil decreased irreversibly due to desiccation, which can be attributed to the plastic deformation of the pores. The water reduction due to drying was higher in the rice monoculture paddy field than in the rotationally cultivated paddy field. However, the continuous wet conditions after harvest induced restoration of 23% to 78% of the pores that evaluated as having been plastically compressed. These observations revealed the limitation of applying the elasto-plastic model to temporal changes in paddy soil structure. The mechanisms which cause time-dependency in shrinkage and swelling should be studied to obtain effective control of the mechanical and hydrological behavior of paddy soil. Application of alternative mechanical models that take into account the time-dependent behavior should also be explored.

Effects of rainfall and manure application on phosphorus leaching in field lysimeters during fallow season

Purpose Transformation and transport of soil phosphorus (P) from chemical fertilizer or manure are affected by agronomic practices (i.e., fertilization, irrigation, and tillage) and numerous abiotic factors (i.e., temperature, drought, and rainfall). Previous studies on the effects of manure application on P loss were mostly conducted during cultivation and often using the laboratory column approach. Validated field observations by integrating P availability with the risk of P loss are few. This study aimed to evaluate the effects of rainfall and manure application on P leaching during fallow season.

Amelioration of the reactive nitrogen flux calculation by a day/night separation in weekly mean air concentration measurements

The low time resolution of air concentration data of atmospheric deposition in regional monitoring networks makes it difficult to estimate fluxes between the land and the atmosphere. The present study was an evaluation of the effects of day/night separation for a low time resolution of air concentration measurements (i.e., weekly mean) for the estimation of reactive nitrogen fluxes. The target chemical species included reactive nitrogen primarily ammonia (NH3) and nitric acid gas (HNO3) and secondarily nitrous acid gas, particulate ammonium, and particulate nitrate in addition to sulfur dioxide (SO2) as a reference. Monitoring was conducted for one year at a single-crop rice paddy field in central Japan. The study period was divided into the cropping and fallow seasons, which were characterized by rice plants or a drained bare soil surface, respectively. The filter-pack method was applied to measure the weekly mean air concentrations with day/night separation for the target species at two heights (6 and 2 m above the ground surface). Both an inferential and a gradient method were applied to calculate the deposition and exchange fluxes, respectively. The day/night separation in a weekly sampling protocol, on average, reduced the underestimation of HNO3 fluxes for the inferential method by 15.2% ± 6.8% and 8.2% ± 6.1% in the cropping and fallow seasons, respectively, and reduced the overestimation of NH3 fluxes for the gradient method by 121% ± 128% in the cropping season. The fluxes calculated using the inferential method agreed relatively well with those calculated using the gradient method for HNO3 and SO2. The use of single-height measurements for air concentrations with day/night separation and flux calculations using the inferential method are recommended as an appropriate way to enhance the quality in calculated fluxes while simultaneously suppress the increase in labor cost.

Impact of Fallow Programs and Fumigants on Nutsedge (Cyperusspp.) Management in Plasticulture Tomato

With the loss of methyl bromide (MeBr) and high prices of alternatives, tomato growers are applying lower fumigant rates or adopting a reduced system. Without the broad-spectrum control provided by the complete fumigant system, a fallow weed program might be needed to avoid an increase in pest pressure with consecutive years of application of the reduced-fumigant system. Nutsedges are among the pests of interest due to their fast reproduction by underground structures and ability to spread and quickly infest a field. Field trials were conducted between February and December of 2011 in Balm, FL, to evaluate the impacts of fallow treatments, fumigants, and halosulfuron on nutsedge control. The trial design was a split–split plot with main, sub-, and subsubplots being fallow, fumigant, and herbicide treatment, respectively. Fallow treatments were spaced evenly throughout the fallow season and consisted of sequential combinations of cultivation (C) and/or glyphosate (G) applied at 2.24 kg ae ha−1; including: C, CC, G, GG, CG, GC, GCG, and NO (nontreated control). Fumigant treatments included a reduced-fumigant system of 1,3-dichloropropene plus chloropicrin 40:60 (1,3-D + pic) at 281 kg ha−1, a complete fumigant system of dimethyl disulfide plus chloropicrin 79:21 (DMDS + pic) at 545 kg ha−1, and no fumigant (NoFum). Herbicide treatments were either two POST applications of halosulfuron at 39 g ai ha−1(Hal) or no halosulfuron (NoHal). In general, the fallow weed treatment GCG was the most effective in reducing nutsedge shoot emergence through the plastic mulch. When the reduced-fumigant system 1,3-D + pic was combined with GCG fallow treatment and halosulfuron (GCG:1,3-D + pic:Hal), no differences were found between this combination and the complete fumigant system DMDS + pic with halosulfuron and combined with CC, G, GG, CG, GC or GCG. This study shows the importance of adding a fallow weed program and halosulfuron to either a reduced or complete fumigation system to minimize the reproduction and growth of nutsedges.

Four-year monitoring of atmospheric ammonia using passive samplers at a single-crop rice paddy field in central Japan

The aim of this study was to clarify the atmosphere-paddy exchange of ammonia (NH3) at a single-crop rice paddy field in central Japan. Measurements of NH3 air concentrations were carried out using passive samplers at two heights above the ground surface (4.0 and 1.5 m) on a weekly basis over a four-year period. The mean NH3 air concentrations ± standard deviations at 4.0 m were 2.5 ± 0.8 and 3.0 ± 1.0 (20°C, 1013 hPa) in the cropping and fallow seasons, respectively. Sharp increases in the NH3 concentrations coincided with the application of poultry manure and post-harvest fieldburning activities; those values exceeded the 95% range of the weekly mean concentrations. The NH3 exchange fluxes were calculated using a gradient method in which the flux was expressed as the product of the difference in air concentrations multiplied by the diffusion velocity between the two heights. The mean NH3 exchange fluxes ± standard deviations were 0.016 ± 0.022 and 0.019 ± 0.115 μg N msof deposition in the cropping and fallow seasons, respectively; where the weekly mean flux was assumed to be zero if the difference in the air concentrations between the two heights was not significant (p < 0.05). In general, the paddy field acted as a net sink of atmospheric NH3, with an annual net deposition of 7–9 kg N hayr-. However, the application of poultry manure in February 2008 induced a strong NH3 emission of approximately 10 kg N haduring three weeks, which nearly counterbalanced the annual deposition for an entire year. Passive samplers are a convenient option for long-term monitoring, although the weekly mean exchange fluxes of NH3 had a systematic error; a case study showed a 66% overestimation for the weekly mean exchange flux.

Optimum application level of winter cover crop biomass as green manure under considering methane emission and rice productivity in paddy soil

The combined seeding and cropping of non-leguminous and leguminous cover crops during the cold fallow season is recommended as an important agronomic practice to improve total biomass productivity and soil fertility in mono-rice (Oryza sativa L.) cultivation system. However, application of plant residues as green manure can increase methane (CH4) emission during rice cultivation and affect rice quality and productivity, but its effects are not well examined. In this field study, the mixture of barley (Hordeum vulgare R.) and hairy vetch (Vicia villosa R., hereafter, vetch) seeds with 75 % recommended dose (RD 140 kg ha−1) and 25 % RD (90 kg ha−1), respectively, were seeded after rice harvesting in late November, 2010, and harvested before rice transplanting in early June 2011. Total aboveground biomass was 36 Mg ha−1 (fresh weight basis with 68 % moisture content), which was composed with 12 Mg ha−1 of barley and 24 Mg ha−1 of vetch. In order to determine the optimum recycling ratio of biomass application that can minimize CH4 emission without affecting rice productivity, different recycling ratios of 0, 25, 50, 75, and 100 % of the total harvested biomass were incorporated as green manure 1 week before rice transplanting in a typical temperate paddy soil. The same rates of chemical fertilizers (N–P2O5–K2O = 90–45–58 kg ha−1) were applied in all treatments. Daily mean CH4 emission rates and total CH4 fluxes were significantly (p < 0.05) increased with increasing application rates of cover crop biomass. Rice productivity also significantly (p < 0.05) increased with biomass application, but the highest grain yield (53 % increase over the control) was observed for 25 % recycling. However, grain quality significantly (p < 0.05) decreased with increasing cover crop application rates above 25 % recycling ratio, mainly due to extended vegetative growth periods of rice plants. Total CH4 flux per unit grain yield, an indicator used to simultaneously compare CH4 emission impact with rice production, was not statistically different between 25 % biomass recycling ratio and the control but significantly increased with increasing application rates. Conclusively, the biomass recycling ratio at 25 % of combined barley and vetch cover crops as green manure might be suitable to sustain rice productivity without increasing CH4 emission impact in mono-rice cultivation system.

Contribution of winter cover crop amendments on global warming potential in rice paddy soil during cultivation

Background and aims Winter cover crop cultivation during the fallow season has been strongly recommended in mono-rice paddy soil to improve soil quality, but its impact in increasing the greenhouse gases (GHGs) emissions during rice cultivation when applied as green manure has not been extensively studied. In order to recommend a preferable cover crop which can increase soil productivity and suppress GHG emission impact in paddy soil, the effect of winter cover crop addition on rice yield and total global warming potential (GWP) was studied during rice cultivation.

Considering winter cover crop selection as green manure to control methane emission during rice cultivation in paddy soil

Cover crop cultivation during the cold fallow season has been strongly recommended in mono-rice cultivation system to improve soil quality. Its addition as green manure could stimulate methane (CH4) emission in the submerged paddy soil during rice cultivation, but its effect has not been evaluated well. Leguminous Chinese milk vetch (hereafter milk vetch) and non-leguminous rye were seeded after rice harvesting in 2008 and 2009, and total above-ground biomasses were incorporated with the recommended mineral fertilizers (NPK+milk vetch, and NPK+rye, respectively) before rice transplanting in 2009 and 2010. No fertilization (control) and mineral fertilization alone (NPK) plots were installed for comparison. Methane flux which was investigated by the closed chamber method during rice cultivation was significantly increased by chemical fertilization to ca. 80–250% over the control (138–141kgCH4ha−1), but increased more markedly by cover crop biomass addition to ca. 28–121% over the NPK treatment. Milk vetch was more effective on stimulating less CH4 emission (28–61% increase over NPK) and improving rice productivity (18–31% increase over NPK) than rye (86–121% increase of CH4 emission and −3–6% of yield increase over NPK). As a result, the total CH4 flux per grain yield was significantly increased by rye addition, but were similar between the NPK+milk vetch and NPK treatments. Conclusively, low C/N ratio cover crop like milk vetch might be more recommendable green manure to minimize CH4 emission impact and increase rice productivity than high C/N ratio cover crop like rye in paddy soil.

Winter wheat grain yield associated with precipitation distribution under long-term nitrogen fertilization in the semiarid Loess Plateau in China

Nitrogen (N) and precipitation are the main limiting factors in food production under rain-fed cropping systems in arid and semiarid regions. A long-term field experiment was conducted from 1984 to 2009 in the Changwu State Key Agro-Ecological Experimental Station of the Loess Plateau, China, to study interactions between precipitation and N fertilization. Winter wheat (Triticum aestivum L.) was grown with N fertilization at 0, 45, 90, 135, and 180kgNha−1. With 25-year N fertilization, soil organic carbon and total N were increased by 18% and 26%, respectively. Mean yields and precipitation use efficiency (PUE) levels with N fertilization were increased by onefold to twofold compared with unfertilized soils. Generally, during the period of 1984–2009, grain yields with 45–`180kgN ha−1 increased at the rate of 38–49kgha−1year−1 (p<0.05), whereas PUE increased at the rate of 0.071–0.088kgmm−1year−1. These increases over time are largely attributable to improvements in soil organic carbon and total N. Variations in yield were proportionally reduced by N fertilization, but heavily depended on the fluctuation of precipitation. Grain yields with 45–180kgN ha−1 decreased by approximately 10%–45% (p<0.05) in the dry years (drought index<−0.35) compared with the normal years, whereas significant increases were not detected in the wet years (drought index>0.35). Grain yields with 90–180kgN ha−1 were positively correlated (p<0.05) with fallow season precipitation, but insignificantly correlated with growing season precipitation. The optimum N fertilization rates in the dry, normal and wet years increased following an increasing sequence of 45, 135 and 180kgNha−1. These results have significant implications for optimizing N fertilization and maximizing yield and PUE in rain-fed cropping systems in arid and semiarid regions.

Age, growth and habitat use of the topmouth gudgeon,Pseudorasbora parvain irrigation ditches on northwestern Kyushu Island, Japan

Summary In Japan, Pseudorasbora parva has not been negatively affected by artificial changes in its habitat. Ecological traits of the species may explain this easy adaptation to artificial habitats. An ecological investigation of P. parva inhabiting irrigation ditches was conducted monthly for approximately two years on northwestern Kyushu Island, Japan. Measurements of 1927 individuals revealed two size classes, maturation age (1 year), and lifespan (1–2 years). Results of this study and previous studies show that the species exhibits life history plasticity. In addition, habitat use of ditches indicates that abundances correlated positively with water temperature and negatively with current velocity in the crop-growing season, and positively with water depth and negatively with current velocity in the fallow season. Structural factors such as ditch revetment conditions and aquatic macrophyte cover were unimportant for this species. The study shows that the gudgeon adapts to artificial ditches easily and successfully because of both life history plasticity and wide-scale use of the habitat.

Estimation of Soil Evaporation During Fallow Seasons to Assess Water Balances for No‐Tillage Crop Rotations

Abstract Estimates of soil evaporation and available soil water of no‐tillage fields under farm conditions are important to assess soil water status at sowing of rainfed grain crops. The objective of this study was to predict stored soil water of no‐tillage fields during the fallow periods following soybean (Glycine max (L.) Merr.) and maize (Zea mays L.) crops by accounting for decreased soil evaporation as a result of the residues left on the soil surface. Three simple phenomenological models were used to simulate stored soil water under field conditions at seven locations in Argentina. Two models calculated decreased soil evaporation based on crop residue mass, and the third assumed a constant fractional decrease in bare soil evaporation. All models gave good estimates of soil water content during the fallow periods following a soybean crop. In cases with large quantities of maize residue, however, the models resulted in more water retention in the soil than observed as a consequence of underprediction of soil evaporation. These results indicate that full benefit of crop residue was not being achieved in these fields, probably due to a failure to finely chop and uniformly distribute the crop material on the soil surface.

A knowledge-based prediction model of Verticillium wilt on potato and its use for rational crop rotation

Verticillium dahliae is the major causal agent of potato early dying (PED) syndrome, characterized by stunting, chlorosis and wilting, premature senescence and early plant dying. It is a common practice to reduce the risk of Verticillium wilt (VW) by applying a rational crop rotation. A knowledge based prediction model for VW was developed and validated. It was based on experimental data and practical management experience, and utilized a knowledge-based approach to acquire the expert knowledge. The potential contribution of this approach was demonstrated in the process of knowledge acquisition and in the model development. The experts identified eight major factors that affect disease development (in descending order of importance): inoculum level in the soil, cultivar susceptibility, fumigation history, frequency of susceptible crops within a crop rotation, growing season, fallow seasons within a crop rotation, infection level in the tubers and soil type. The procedure used for selecting the factors and the method used for extracting their relative weights (pairwise comparison) was proved to be useful as the factor and their relative weights replicated the conclusions of studies from other sites. Additionally, the prediction model was found to be 80% accurate. The prediction model was integrated in a spatial decision support system (SDSS), built under ArcGIS 10, that advises the farmer on plot allocation for potato growing with minimal risk of VW. The SDSS interface and its outputs are presented using real-world data. Effective use of the SDSS by farmers requires the construction of a historical database that includes values of the abovementioned factors and a user-friendly interface for routine updating.

Atmosphere-rice paddy exchanges of inorganic particles and relevant gases during a week in winter and a week in summer

The aim of the present study was to investigate the air concentrations (mass concentration) and exchange fluxes of inorganic particles, i.e., water-soluble inorganic components in fine and coarse particles, and relevant gases at a paddy field for the single cropping of rice in central Japan. The target chemical species were ammonium (pNH4), nitrate (pNO3), nitrite (pNO2), sulfate (pSO4), and chloride (pCl) for inorganic particles separated into coarse and PM2.5 fractions and ammonia (NH3), nitric acid (HNO3), nitrous acid (HNO2), sulfur dioxide (SO2), and hydrochloric gas (HCl) for the relevant gases. Intensive observations were conducted for approximately one week in the winter of 2009 as a fallow season (winter 2009) and in the summer of 2010 at the heading stage of paddy rice (summer 2010). The filter-pack and gradient methods were used to determine the air concentrations and the exchange fluxes, respectively. The air concentrations of the coarse particles were lower than those of the PM2.5 except pCl and pNO3 in the summer of 2010. The ion balance of PM2.5 implied an acidic condition in the daytime in summer 2010 but neutral conditions at other times. Ammonia showed the highest air concentrations and the largest exchange fluxes in most cases among all target species. The paddy field was usually a sink for the inorganic particles and relevant gases; however, NH3 emission in the summer of 2010, perhaps from the paddy rice, occasionally occurred when the air concentrations of NH3 became very low.

Carbon isotopic composition, methanogenic pathway, and fraction of CH4oxidized in a rice field flooded year-round

[1] Values of δ13C were investigated of CH4 trapped in the soil pore water and floodwater of and emitted from a rice field under continuous flooding throughout the fallow and following rice seasons, and CH4 produced via different pathways and fraction of CH4 oxidized was calculated by using the isotopic data. Pore water CH4 was relatively 13C depleted, with δ13C values about −65‰ over the season except between July and August (around −55‰). Also, hydrogenotrophic methanogenesis was very important (around 50%) for most of the season, while acetoclastic methanogenesis dominated (about 70%) only between July and August. Floodwater CH4 was heavier in δ13C value (from −50‰ to −34‰) than pore water CH4 (from −68‰ to −54‰) over the season, demonstrating that it is highly influenced by methanotrophy. The δ13C value of emitted CH4was negatively correlated with flux in temporal variation (P <0.05), and it was more positive in the fallow season (between −56‰ and −44‰) than in the rice season (between −68‰ and −48‰). This indicates that plant-mediated CH4 transport is probably a more important pathway and causes less CH4 oxidation during the rice season than during the fallow season, which is further confirmed by the fraction of CH4 oxidized being generally greater in the fallow season (60%–90%) than in the rice season (10%–80%). These findings suggest a low contribution of acetoclastic methanogenesis and a high fraction of CH4 being oxidized in the field, especially in the fallow season.

Different response of silicate fertilizer having electron acceptors on methane emission in rice paddy soil under green manuring

Cultivation of green manure plants during the fallow season in rice paddy soil has been strongly recommended to improve soil properties. However, green manuring may impact greenhouse gas emission, methane (hereafter, CH4) in particular, under the flooded rice cultivation and thus, application of chemical amendments being electron acceptors can be an effective mitigation strategy to reduce CH4 emissions in irrigated rice (Oryza sativa L.) field amended with green manure. To investigate the effect of iron (Fe) slag silicate fertilizer (hereafter, silicate fertilizer), which was effective in reducing CH4 emission and increasing rice productivity, in green manure-amended paddy soil, the aboveground biomass of Chinese milk vetch (hereafter, vetch) was added at rates of 0, 10, 20, and 40 Mg (fresh weight) ha−1 before the application of silicate fertilizer, which was added at rates of 0 and 2.3 Mg ha−1. Silicate fertilization reduced the seasonal CH4 flux by ca. 14.5% and increased rice yield by ca. 15.7% in the control (no vetch application) treatment. However, CH4 production was increased by silicate fertilization in vetch-treated soil particularly at the initial rice growing stage, which was probably due to the enhanced decomposition of added organic matters by the silicate liming effect. In conclusion, silicate fertilization is not effective in reducing CH4 production in green manure-amended rice paddy soils and its use should be properly controlled.

Nitrogen loss from a mixed land use watershed as influenced by hydrology and seasons

Summary Non-point nitrogen (N) loss from agriculture is an environmental concern among scientists, decision-makers, and the public. This study investigated NO3–N and total N losses from a mixed land use watershed (39.5 ha) in the Appalachian Valley and Ridge Physiographic Province as influenced by hydrology (flow type, runoff volume, storm sizes, and precipitation amount) and seasons (pre-growing, growing, and post-growing seasons) from 2002 to 2006. Stream discharge was monitored every 5-min and water samples for NO3–N and total N analyses were collected weekly for base flow and for every storm. The majority of NO3–N (about 75%) and total N (about 65%) were exported in base flow, which contributed about 64% of the total flow in an average year and had greater flow-weighted mean NO3–N concentration (5.6 mg L−1) than storm flow (3.4 mg L−1). A substantial proportion of total N was in the form of NO3–N in base flow (58.1%) and small storms with 73% of the overall NO3–N and total N losses. These two seasons also had greater flow-weighted mean NO3–N (4.8 and 5.5 mg L−1, respectively) and total N (9.8 and 10.1 mg L−1, respectively) concentrations and greater discharge (40% and 32% of total discharge, respectively) than during the growing season. Greater contribution of NO3–N to total N loss in storm flow was also observed during the pre-growing and post-growing seasons than during the growing season, while contribution of NO3–N to total N loss in base flow was consistent across seasons. Management practices to reduce N loss from this watershed should target periods of base flow when NO3–N and total N concentrations are greater (before and after the crop growing season) and target areas along the stream where seeps are present, perhaps including perennial plant species in localized riparian buffers and introducing cover crops on the agricultural land during the fallow season.

Effects of a catch crop and reduced nitrogen fertilization on nitrogen leaching in greenhouse vegetable production systems

Greenhouse vegetable cultivation has greatly increased productivity but has also led to a rapid accumulation of nitrate in soils and probably in plants. Significant losses of nitrate–nitrogen (NO3-N) could occur after heavy N fertilization under open-field conditions combined with high precipitation in the summer. It is urgently needed to improve N management under the wide spread greenhouse vegetable production system. The objective of this study was to evaluate the effects of a summer catch crop and reduced N application rates on N leaching and vegetable crop yields. During a 2-year period, sweet corn as an N catch crop was planted between vegetable crops in the summer season under 5 N fertilizer treatments (0, 348, 522, 696, and 870 kg ha−1) in greenhouse vegetable production systems in Tai Lake region, southern China. A water collection system was installed at a depth of 0.5 m in the soil to collect leachates during the vegetable growing season. The sweet corn as a catch crop reduced the total N concentration from 94 to 59 mg l−1 in leached water and reduced the average soil nitrate N from 306 to 195 mg kg−1 in the top 0.1-m soil during the fallow period of local farmers’ N application rate (870 kg ha−1). Reducing the amount of N fertilizer and using catch crop during summer fallow season reduced total N leaching loss by 50 and 73%, respectively, without any negative effect on vegetable yields.

Responses of soil water balance and precipitation storage efficiency to increased fertilizer application in winter wheat

Increased fertilizer use over many years may have detrimental effects on crop production due to its high soil water consumption in rainfed regions. In this study, based on a long-term fertilization experiment initiated in 1984, we report the effect of increased fertilization on soil water balance, precipitation storage efficiency (PSE), yield and water use efficiency of winter wheat from 2005 to 2009. The experimental design consisted of a control treatment (CK) and three fertilizer treatments: nitrogen, phosphorus and manure (NPM), nitrogen and phosphorus (NP), and nitrogen (N). Soil water storage in NP and NPM was significantly lower than that in CK and N at both harvest and planting time. Compared with the CK, on average, treatments N, NP and NPM increased soil water recharge during the fallow period by 11%, 22% and 17%, and they also increased soil water depletion during growing season by 17%, 23% and 23% (P < 0.05), respectively. The average value of annual soil water balance was positive for all treatments, and was not significantly different among treatments. Increased fertilizer application significantly (P < 0.05) increased PSE during the summer fallow periods, and the average PSE was 28%, 32%, 34% and 33% for CK, N, NP and NPM, respectively. Wheat yield and water use efficiency increased significantly after long term fertilization, especially for treatments NP and NPM. The results indicated that more of rainfall was used for evapotranspiration and less was lost during the fallow season for the high fertility treatments after long term fertilizer application. In the long run, such changes in water use pattern could help to improve the sustainability of winter wheat production.

Sustainability of maize-based cropping systems in rural areas of Zimbabwe: an assessment of the residual soil fertility effects of grain legumes on maize (&lt;I&gt;Zea mays&lt;/I&gt; [L.]) under field conditions

The residual soil fertility benefits of the preceding legumes to the following maize crop were demonstrated in the study. Incorporating stover of Bambara nut, cowpea, groundnut dry bean and soyabean gave higher maize yields compared to plots where the stover was removed. Total maize dry matter yield increases of 1.30 tha-¹ to 5.19 ha-¹ were recordedfollowing legume stover incorporation compared to stover removal. Even removal of stover of these same legumes gave significant maize yield increases compared to those from the maize after maize or after fallow plots. The total maize dry matter yield was greater after legumes with stover removed (ranging from 4.41 to 9.91 tha-¹) than after maize (2.16 to 2.26 tha-¹) or one season fallow (1.57 to 1.84 tha-¹). So farmers who keep livestock can still remove legume residues as fodder to supplement grazing in the dry winter period and still benefit from improved maize yields. International Journal of Engineering, Science and Technology, Vol. 2, No. 7, 2010, pp. 141-148

Case study on effects of water management and rice straw incorporation in rice fields on production, oxidation, and emission of methane during fallow and following rice seasons

To investigate production, oxidation, and emission of methane (CH4) in rice fields during the fallow and following rice seasons as affected by water management and rice straw incorporation in the fallow season, field and incubation experiments were carried out from November 2007 to November 2008. Four treatments, i.e. two water managements (flooded and drained) and two rates of rice straw application (0 and 4.8 t/ha), were laid out in a randomised block design. Results show that obvious CH4 production occurred in flooded fields in the late fallow season; consequently, fallow CH4 emission contributed 9.6–33.1% to the annual total emission. However, emission mainly occurred during the rice season. During the rice season, the mean CH4 production potential in flooded fields was 2.6–3.8 times that in drained fields, making the total CH4 emission 2.1–2.5 times that in drained fields. Rice straw incorporated in flooded fields significantly increased production and emission of CH4 during both the fallow and the following rice seasons (P &lt; 0.05), but in drained fields, no significant effect was observed (P &gt; 0.05). There was no significant difference in mean CH4 oxidation potential between the treatments (P &gt; 0.05), indicating that water management and rice straw incorporation in the fallow season have little influence on CH4 oxidation during the fallow and following rice seasons. Based on the findings, water management and rice straw incorporation in the fallow season significantly affected CH4 emission during the fallow and the following rice seasons by influencing CH4 production rather than CH4 oxidation in fields.