Winter Fallow Season Research Articles

Methanogenic Pathway and Fraction of CH4 Oxidized in Paddy Fields: Seasonal Variation and Effect of Water Management in Winter Fallow Season

A 2-year field and incubation experiment was conducted to investigate δ13C during the processes of CH4 emission from the fields subjected to two water managements (flooding and drainage) in the winter fallow season, and further to estimate relative contribution of acetate to total methanogenesis (Fac) and fraction of CH4 oxidized (Fox) based on the isotopic data. Compared with flooding, drainage generally caused CH4, either anaerobically or aerobically produced, depleted in 13C. There was no obvious difference between the two in transport fractionation factor (εtransport) and δ13C-value of emitted CH4. CH4 emission was negatively related to its δ13C-value in seasonal variation (P<0.01). Acetate-dependent methanogenesis in soil was dominant (60–70%) in the late season, while drainage decreased Fac-value by 5–10%. On roots however, CH4 was mostly produced through H2/CO2 reduction (60–100%) over the season. CH4 oxidation mainly occurred in the first half of the season and roughly 10–90% of the CH4 was oxidized in the rhizosphere. Drainage increased Fox-value by 5–15%, which is possibly attributed to a significant decrease in production while no simultaneous decrease in oxidation. Around 30–70% of the CH4 was oxidized at the soil-water interface when CH4 in pore water was released into floodwater, although the amount of CH4 oxidized therein might be negligible relative to that in the rhizosphere. CH4 oxidation was also more important in the first half of the season in lab conditions and about 5–50% of the CH4 was oxidized in soil while almost 100% on roots. Drainage decreased Fox-value on roots by 15% as their CH4 oxidation potential was highly reduced. The findings suggest that water management in the winter fallow season substantially affects Fac in the soil and Fox in the rhizosphere and roots rather than Fac on roots and Fox at the soil-water interface.

Molecular characterization of methane-oxidizing bacteria associated with rice straw decomposition in a rice field

Methane-oxidizing bacteria (MOB) are crucial to the reduction of CH4 emitted to the atmosphere. However, it is unclear how MOB in rice straw are affected by straw decomposition processes. In a Japanese rice field, a year-round experiment was set up to study the effects of agricultural practice (rice cultivation/winter fallow), straw parts (leaf sheath/blade) and the site of straw placement (plow layer/soil surface) on MOB communities in rice straw using denaturing gradient gel electrophoresis (DGGE) and DNA sequencing analyses of key MOB functional genes (pmoA and amoA). Thirty-eight different DGGE bands were observed over the entire investigation period. Principal component analysis of DGGE pattern suggested that agricultural practice is the key factor regulating the MOB communities. Sequencing of dominant DGGE bands showed that: (1) during the rice cultivation period, methanotrophs (particularly type I methanotrophs) dominated the MOB community, (2) during the winter fallow season both type I and type II methanotrophs were dominant in sheath segments placed both on the soil surface and in the plow layer, whereas ammonia oxidizers seemed to dominate blade segments placed in the plow layer. Alignment of diagnostic amino acid sequences of MOB suggested the presence of novel ammonia oxidizers in rice straw in rice fields.

The effects of moisture and temperature on the survival of Colletotrichum acutatum on strawberry residue in soil

Strawberry stolons inoculated with Colletotrichum acutatum, the causal agent of strawberry anthracnose, were buried in autoclaved or nonautoclaved Reiff fine sandy loam soil and kept at 5 or 10 °C in controlled environment chambers. Samples were examined monthly for 6 months to determine the survival of the pathogen from the number of recovered conidia and the percent conidial germination. Two soil moisture levels, with water contents of 26.8 or 35.3 g per 100 g of dry soil, were maintained at each temperature. Three isolates of C. acutatum (Wolfskill, Surecrop, and 102) from California strawberry performed similarly at the same temperature. The number of conidia recovered and percent conidial germination were the highest at 5 °C with a soil moisture level of 26.8%. Conidia recovered from buried stolons decreased progressively over the 6 months, from 5 × 104 to 0.5 × 104 per linear centimeter of lesion on stolons. The decline was more pronounced at 10 °C than 5 °C and at a higher soil moisture. Percent conidial germination remained between 80% and 90% for 4 to 5 months, fell to 40%–60% in the last period, and was particularly low at 10 °C and high soil moisture. Our results indicated that C. acutatum may survive the relatively short winter fallow season in strawberry nursery soil in California.

Tillage practices for soil and water conservation in the semi-arid zone I. Management of fallow during the rainy season preceding cotton

Field and laboratory experiments were conducted on a crusting loess soil in the northern Negev (Israel) with the aim of improving the efficiency of the use of rain by row crops, either in dryland or irrigated farming, and to decrease erosion. The specific objective of the experiments described was to develop methods that enhance infiltration of rainfall during the winter fallow season in an area with a mean annual rainfall of 400 mm which is subject to wide variation. It was found that the traditional tillage system consisting of deep ploughing (35–45 cm) of dry soil in the fall followed by disking, smoothing and ridging is the worst choise as it could result in runoff losses of as much as 60% of the rainfall, accompanied by accelerated erosion. This water loss can be critical to the success of dryland cotton and also determines whether or not a pre-irrigation of about 25% of the total annual water allotment must be given to irrigated cotton. The traditional practice was compared with: deep ploughed land left fallow during the entire rainy season; ridging after subsoiling instead of deep ploughing; subsoiling and ridging carried out in one minimum tillage operation; direct ridging without primary tillage and basin tillage of ridges following either deep ploughing, subsoiling or minimum tillage. This study showed that by far the most effective method for enhancing infiltration and eliminating runoff was the basin tillage system. The method is adaptable both to mechanized farming and to farming based on animal power or manual labour, and its application can ensure success where rainfall is limiting. It was found that laboratory characterization of soil hydraulic properties with a static rainfall simulator allows prediction of runoff on crusting soils. This means that the need for, and the effectiveness of, conservation measures may be estimated using disturbed soil samples, which is quicker and cheaper than field tests.