Ecosystem Services Provided by Cover Crops and Biofumigation in Sunflower Cultivation

In south-western France, sunflowers are usually grown in short rotations and after a long fallow period during which soils are left bare. This practice can favour diseases, caused by soilborne fungi, such as sunflower verticillium wilt (SVW), as well as nitrate leaching, both of which can decrease yields. Growing cover crops during a fallow period is an agroecological practice that could provide ecosystem services and mitigate SVW. A Brassicaceae cover crop that causes biofumigation produces glucosinolates and liberate biocidal compounds that might regulate SVW biologically. Moreover, the green manure effect of the Fabaceae might increase soil mineral nitrogen (SMN). To go further, mixtures of Brassicaceae and Fabaceae might mutualise the benefits that each cover crop has in sole crops. A four-year field study in south-western France tested Brassicaceae (brown mustard, turnip rape and fodder radish) and Fabaceae (purple vetch) in sole crops or a mixture with two or three species during the fallow period, followed by biofumigation, and sunflower crop. The cover crops were characterised, SMN was measured, the SVW and yield were assessed and compared to those of the crop grown on soils left bare during the fallow period. Purple vetch as a sole crop cover crop significantly increased SMN before sunflower sowing but only in 2019. Fodder radish as a sole crop reduced SVW severity significantly, overall, 80 days after sowing, except in 2019, when weather conditions were unfavourable to biofumigation. Purple vetch as a sole crop also reduced significantly SVW severity in 2017 and 2020. Finally, sunflower yields after cover crops were higher than those after bare soils, only after purple vetch as a sole crop in 2020, with a mean increase of 0.77 t ha−1. Mixtures of Brassicaceae and Fabaceae sowed at these densities resulted in an intermediate SMN level between those in sole crops and the bare soil and they did not significantly decrease SVW or increase yields. Our results suggest that cover crops, especially fodder radish or purple vetch, and biofumigation can provide ecosystem services for sunflower, instead of leaving soils bare during the fallow period. However, the extent of ecosystem services is markedly affected by soil and climatic conditions as well as other management practices.

Continuous Maize Cropping Accelerates Loss of Soil Organic Matter in Northern Thailand as Revealed by Natural 13C Abundance

AimsThe loss of soil organic matter (SOM) has widely been reported in the tropics after changing land use from shifting cultivation to continuous cropping. We tested whether continuous maize cultivation accelerates SOM loss compared to upland rice and forest fallow. Methods: Because litter sources include C4 plants (maize in maize fields and Imperata grass in upland rice fields) in Thailand, C3-derived and C4-derived SOM can be traced using the differences in natural 13C abundance (δ13C) between C3 and C4 plants. We analyzed the effects of land use history (cultivation or forest fallow period) on C stocks in the surface soil. Soil C stocks decreased with the cultivation period in both upland rice and maize fields. ResultsThe rate of soil organic carbon loss was higher in maize fields than in upland rice fields. The decomposition rate constant (first order kinetics) of C3-plant-derived SOM was higher in the maize fields than in the upland rice fields and the C4-plant-derived SOM in the forest fallow. Soil surface exposure and low input of root-derived C in the maize fields are considered to accelerate SOM loss. Soil C stocks increased with the forest fallow period, consistent with the slow decomposition of C4-plant-derived SOM in the forest fallows. ConclusionsContinuous maize cultivation accelerates SOM loss, while forest fallow and upland rice cultivation could mitigate the SOM loss caused by continuous maize cultivation.

Effects of fallow tillage on winter wheat yield and predictions under different precipitation types

In northern China, precipitation that is primarily concentrated during the fallow period is insufficient for the growth stage, creates a moisture shortage, and leads to low, unstable yields. Yield prediction in the early growth stages significantly informs field management decisions for winter wheat (Triticum aestivum L.). A 10-year field experiment carried out in the Loess Plateau area tested how three tillage practices (deep ploughing (DP), subsoiling (SS), and no tillage (NT)) influenced cultivation and yield across different fallow periods. The experiment used the random forest (RF) algorithm to construct a prediction model of yields and yield components. Our results revealed that tillage during the fallow period was more effective than NT in improving yield in dryland wheat. Under drought condition, DP during the fallow period achieved a higher yield than SS, especially in drought years; DP was 16% higher than SS. RF was deemed fit for yield prediction across different precipitation years. An RF model was developed using meteorological factors for fixed variables and soil water storage after tillage during a fallow period for a control variable. Small error values existed in the prediction yield, spike number, and grains number per spike. Additionally, the relative error of crop yield under fallow tillage (5.24%) was smaller than that of NT (6.49%). The prediction error of relative meteorological yield was minimum and optimal, indicating that the model is suitable to explain the influence of meteorological factors on yield.

Impact of Small-Scale Mining Activities on Physicochemical Properties of Soils in Dunkwa East Municipality of Ghana

The quality of soils in rehabilitated small-scale mined sites needs thorough investigation since a lot of changes do occur. The study assessed the impacts of small-scale mining activities on concentration and distribution of soil physicochemical properties and heavy metals. The soil samples were collected from 120 (50 m × 50 m) plots. The concentrations of soil physicochemical properties (Ca, Mg, Na, N, P, K, and OC and EC) varied significantly ( p < 0.05) between unmined and mined soils. However, there were no statistically, significant differences ( p < 0.05) observed in the concentrations of Cd, Hg, Pb, As, and Cu between the unmined and mined soils. Despite the generally poor (33.8%) soil quality in the study area, mining activities further reduced it by 24.2%. Soils from mined sites with unfilled/partially filled pits had higher levels of K, Mg, and Na. As mined sites fallow period increased, concentrations of OC and Cd increased, while Ca, Mg, pH, Cu, Pb, and As and value of EC decreased. The number of years that mined land remained fallow, and whether the pits were filled or unfilled during this period should be factored into the mined land rehabilitation processes.

Characterisation of rice fallow period for increasing cropping intensity in Khordha district of Odisha

The possibility of increasing the cropping intensity in Khordha district was assessed by block-wise characterisation of rainfall, soil texture, available water holding capacity of soil and district level temperature during the rice fallow period as well as deciding the appropriate sowing window for both kharif and rabi crops. More than 50% chances of occurrence of wet weeks at the beginning of the kharif season (20-22 SMW) indicated that the summer ploughing and initial seed bed preparation could be taken up during the period followed by sowing of rice from 23 SMW. The 42-43 SMW with greater than 30% initial probability of wet week at 20 mm threshold limit. Considering the length of growing period (LGP) available, the adjustment of rice variety duration by 10-15 days in medium land and advancement of pulse sowing almost by 15 days before harvest of the rice crop (Pira crop) in low land was registered as the best su suitable option for rabi pulses to ensure better utilisation of rice fallow. In addition to these, harvesting surplus water during kharif and storing in farm ponds for judicious utilisation during rabi season further enhanced the possibility of utilisation of rice fallow and increasing the cropping intensity. In the event of delayed monsoon the rice duration has to be adjusted accordingly not to sacrifice the designated suitable period for rabi pulses.

The Fallow Period Plays an Important Role in Annual CH4 Emission in a Rice Paddy in Southern Brazil

Paddy fields are significant anthropogenic sources of methane (CH4) emissions. In southern Brazil, rice is grown in lowland flooded areas once a year, followed by a long fallow period. This study aimed to measure CH4 fluxes in a rice paddy field in southern Brazil during the rice-growing season of 2015/2016 and the following fallow period. The fluxes were estimated using the eddy covariance (EC) technique and soil chamber (SC). Diurnal and seasonal variations of CH4 fluxes and potential meteorological drivers were analyzed. The CH4 fluxes showed distinct diurnal variations in each analyzed subperiod (vegetative, reproductive, pre-harvest, no rice, and land preparation), characterized by a single-peak diurnal pattern. The variables that most influenced methane emissions were air and surface temperatures. In the growing season, the rice vegetative stage was responsible for most of the measured emissions. The accumulated annual emission estimated was 44.88 g CH4 m−2 y−1, being 64% (28.50 g CH4 m−2) due to the rice-growing season and 36% (16.38 g CH4 m−2) due to the fallow period. These results show the importance of including fallow periods in strategies to mitigate methane emissions in flood irrigated rice-growing areas.

Intensification of Cropping through Utilization of Fallow Period and Unutilized Land Resources in Bangladesh

Unavailability of suitable technologies including stress-tolerant cultivars, management options, irrigation facilities as well as extension supports are the key challenges for intensification of cropping through horizontal and vertical extension approaches. This study assesses the potential for increasing rice production through a horizontal extension approach. Historical and projected trend of area and production of rice, major cropping patterns and cropping intensity, as well as expert opinion, were the basis for extrapolation of the intensity of cropping by 2030. The analysis shows that about 1.52 M ha area with fallow period of the existing major cropping patterns and 0.65 M ha fallow land is potential for additional rice cropping. Resulting from that about 5.8 million tons additional rice can be added to total rice production in the country. An inclusion of a rice crop in certain percentage of the existing major cropping patterns, such as Boro-Fallow-T. Aman (25%), Boro-Fallow-Fallow (50%) and Fallow-Fallow-T. Aman (40%) may contribute, respectively 1.38 million tons, 1.57million tons and 0.80 million tons of rice in the total rice production. Besides, the addition of a certain percentage of cultural waste (50%), marshy land (25%), newly developed char land (50%), and Jhum (60%) and other extrapolation areas of Chittagong Hill Tract, respectively may contribute 0.4 million tons, 0.25 million tons, 0.34 million tons and 0.06 million tons rice in the total rice production. Strategic policy supports are required for implementing appropriate action plans to achieve the goals. Bangladesh Rice J. 25 (1) : 89-100, 2021

Dry bolls and their association with Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae) survival through cotton fallow periods

The boll weevil, Anthonomus grandis grandis Boheman (Coleoptera: Curculionidae), can remain inside dry and deformed reproductive structures of cotton, Gossypium hirsutum Linnaeus (Malvaceae), known as dry bolls, during the cotton fallow to infest the next cotton crop. In this study, the influence of cotton cultivars and sowing densities on the formation of dry bolls was evaluated. In addition, dry bolls were dissected and internal structures that were related to boll weevil development were estimated. Finally, the presence and survival of boll weevils inside dry bolls were evaluated. The results indicate that the number of dry bolls, empty pupal cells, and emergence holes was influenced by cultivar and not by sowing density. Almost one-quarter (22.53%) of adult boll weevils examined was found alive inside the dry bolls after 10 weeks, which is slightly longer than the duration of cotton fallow in Brazil’s main cotton-producing regions. Therefore, remaining inside the dry bolls is an important survival strategy for boll weevils during the cotton fallow period, and cotton cultivars with a greater propensity for the formation of dry bolls might favour survival of the pest during this period.

Do pesticide residues have enduring negative effect on macroinvertebrates and vertebrates in fallow rice paddies?

Rice is one of the most important staple food in the world, with irrigated rice paddies largely converted from natural wetlands. The effectiveness of rice fields in help preserve species depends partially on management practices, including the usage of pesticides. However, related studies have focused predominately on the cultivation period, leaving the effects of soil pesticide residues on aquatic invertebrates during the fallow periods little explored; other animals, such as waterbirds, also rely on aquatic invertebrates in flooded fallow fields for their survival. We therefore investigated vertebrates and macroinvertebrates (terrestrial and aquatic) on rice stands and in flooded water during cultivation and fallow periods in organic and conventional rice fields in Taiwan. Association of environmental factors with terrestrial and aquatic organisms was also analyzed. In total, 32,880 individuals of 144 invertebrate families and 381 individuals of 15 vertebrate families were recorded after nine samplings each for six organic and six conventional rice fields. Family richness and abundance of all invertebrates (terrestrial and aquatic) were higher in organic than in conventional fields during the cultivation period, but were similar between the two agricultural practices during the fallow period. Richness and abundance of terrestrial invertebrates in both organic and conventional fields increased with the progression of rice cultivation, so did the differences between the two practices. Richness of aquatic invertebrates was mostly constant across the sampling period, while abundance increased but differences decreased during the fallow period. Richness and abundance of terrestrial invertebrates were positively associated with ambient temperature and height of rice stand. Abundance of aquatic invertebrates were positively associated with pH value and amount of dissolved oxygen but negatively associated with water temperature. Richness and abundance of all vertebrates and each of the constituting groups (fish, amphibian, reptile, bird, and migratory waterbird) were statistically similar between the two practices although abundance of migratory waterbirds in organic fields were two times those in conventional fields during the fallow period. Our study suggested accumulated effects of pesticides on suppressing terrestrial invertebrates during the cultivation period, but diminishing effects of pesticide residues on repressing aquatic invertebrates during the fallow period. This comprehensive study provided a holistic picture on macroinvertebrate and vertebrate fauna, as well as ramifications of pesticide usage, in a representative Southeast Asia rice paddy ecosystem. Further study should compare rice fields with natural wetlands to better assess how to capitalize on agroecosystems for biodiversity conservation.