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• Net primary production (NPP) as C input source was higher in rice cropping season than fallow season. • Mineralized C loss as C output source was much higher in cold fallow season than warm cropping season. • Net ecosystem C budget (NECB) was negative in the conventional farming system (NPK). • Cover cropping and its biomass incorporation significantly increased soil C stock. In temperate paddy fields, rice is generally cultivated under flooding for 100–140 days during summer season, and thereafter, the soil is left without management under dried soil condition during cold fallow season. In this area rice straw is mostly removed for cattle feeding. Therefore, soil organic carbon (SOC) stock could be decreased with conventional practices, but the seasonal changes of SOC stock have not been evaluated well. To investigate SOC stock changes in temperate rice paddy, two seasonal C balances during rice cropping and fallow season were compared by the net ecosystem C budget (NECB) in the chemical fertilizer (control) and two different green manure treatments for three years. In the control treatment only chemical fertilizer was conventionally fertilized for rice cropping, but maintained without human control during the fallow season. In two green manure treatments, barley and hairy vetch (hereafter, vetch) were cultivated during the fallow season, and their whole biomasses were incorporated before rice transplanting. The conventional soil management with only chemical fertilization decreased small level of SOC stock (minus 0.70–0.84 Mg C ha−1 y−1 of NECB), which was attributed by high harvest removal (approximately 70% of total C input) and mineralized C loss (30%). Cover cropping and its biomass recycling as green manure was effective to increase SOC stock. High C/N ratio of non-leguminous barley produced high biomass yield, and its biomass incorporation significantly increased SOC stock with 1.21–3.43 Mg C ha−1 y−1 of annual NECB. In comparison low C/N ratio of leguminous vetch application increased slightly SOC stock (0.17–1.34 Mg C ha−1 y−1 of NECB), due to low biomass productivity and high mineralized C loss. However, irrespective with fertilization background, approximately 70% of mineralized C loss were occurred during the cold fallow season. Rice grain yields were similar between the control and hairy vetch treatment, but around 10% lower in barley treatment. Conclusively, high C/N ratio of cover crop cultivation during the fallow season could be better to increase SOC stock in mono-rice paddy, but additional nutrient management to increase rice productivity should be developed for barley utilization as green manure. [ABSTRACT FROM AUTHOR]

Background and aims: Crucifers grown as cover crops are known to reduce sulphate leaching (S catch-crop service) and release large amounts of mineral sulphate for the subsequent cash crop once incorporated into the soil (S green-manure service). Crucifer-legume cover crop mixtures are effective to obtain high nitrogen related services, but few data exist on their performances for S-related services. Our study aimed to assess performances of a wide variety of bispecific crucifer-legume mixtures designed to provide soil S catch-crop and S green-manure services.Methods: A two-year field experiment was conducted at two sites near Toulouse, France (silt clay loam soil) and Orléans, France (sandy loam soil) in which cultivars from eight crucifer species and nine legume species were tested as sole and bispecific cover crops.Results: Crucifer-legume mixtures and crucifer sole cover crops provided the same level of S catch-crop service (12 kg S ha−1), significantly higher than that of legume sole cover crops (4 kg S ha−1). Similarly, crucifer-legume mixtures provided almost the same level of S green-manure service (5.5 kg S ha−1) as crucifer sole cover crops (6.5 kg S ha−1).Conclusion: Our results demonstrate the compatibility and complementarity of certain crucifer and legume species when grown together to provide S and N catch-crop and green-manure services. For a same cover crop species no strong cultivar effect has been highlighted in our growing conditions. [ABSTRACT FROM AUTHOR]

Legume hairy vetch and non-legume barley mixtures are broadly cultivated to improve the value of cover crops in mono-rice paddies. Nevertheless, the effects of mixing conditions of the two cover crops on biomass and nutrient productivities and on the yield characteristics of subsequent rice crops have not been well studied. To evaluate the effects of mix-seeding legume and non-legume cover crops on the value of green manure in paddy soil, barley and hairy vetch were sown at the rice harvesting stage as pure crops at the recommended rates (180 kg ha −1 of barley, B100; 90 kg ha −1 of hairy vetch, V100), and as mixtures, in which the two cover crops were mix-seeded with varying seed ratios according to the replacement principle. The mixed seeding of the two crops significantly increased the cover crop biomass and nutrient productivities compared with the single barley and hairy vetch cultivation. Biomass productivity linearly increased with increasing barley seeding level, but it was not affected by the hairy vetch seeding rate. The total N content of the barley biomass clearly increased as the proportion of the total biomass accounted for by hairy vetch was increased, and this significantly improved the value of the green manure of cover crop biomass. In contrast, the total N content of the hairy vetch biomass was not affected by changes in the barley proportion. Biomass produced in the pure barley seeding could not produce the nutrients required by the recommended chemical fertilization level (N–P 2 O 5 –K 2 O = 90–45–57 kg ha −1 ) for rice, but the biomass increase caused by mixed seeding of the two cover crops resulted in enough nutrients to satisfy the recommended fertilization level. The highest biomass and nutrient yields were observed for the mixed seeding of barley and hairy vetch at 25 and 75% (B75V25) of their respective recommended seeding rates. This increased nutrient input stimulated the rice plant growth and significantly improved the rice yields. The highest yields were achieved with the B75V25 treatment. In conclusion, mixed seeding of legume hairy vetch and non-legume barley could be a very useful agronomic practice for increasing the cover crop biomass and its nutrient productivity and to improve the productivity of subsequent rice crops in temperate rice paddies. [ABSTRACT FROM AUTHOR]

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Abstract: 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 (138–141kgCH4 ha−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. [Copyright &y& Elsevier]

Abstract: The benzoxazinoid 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) is produced by rye (Secale cereale) and may contribute to plant-parasitic nematode suppression when rye plants are incorporated as a green manure. We investigated the fate of DIBOA in soil and DIBOA''s effects on nematode reproduction. Soil in plastic bags was treated with DIBOA at concentrations ranging from 1.1 to 18 μg g−1 dry soil, and with the root-knot nematode Meloidogyne incognita. Control soils were treated with water or with 0.31% methanol, with or without nematodes. DIBOA concentrations extracted from the soil were measured at selected times for 5 consecutive days. The soil from each bag was then placed into a pot in the greenhouse, and a cucumber seedling was transplanted into each pot. Five weeks later, only the highest DIBOA concentration, 18 μg g−1 soil, reduced nematode egg numbers. At 0 h, DIBOA measured in soil ranged from 19.68 to 35.51% of the initial DIBOA concentration, and was dependent on the concentration added to the soil. DIBOA half-life was from 18 to 22 h, and very little DIBOA was present in soil after 120 h. Identified breakdown products accounted for only 4% at maximum of the initially added DIBOA. The results of our study demonstrate that high soil concentrations of DIBOA are necessary to suppress M. incognita; DIBOA may not be a major factor in nematode suppression by a rye cover crop. [Copyright &y& Elsevier]