Puddled soils

Irrigated. Grown in levelled, bunded fields with good water control. Crop is fiansplanted or direct seeded in puddled soil, and a shallow floodwater is maintained on the soil surface so tiiat the soil is predominantly anoxic during crop growth. 

Rainfed lowland. Grown in level to gently sloping, bunded fields that are flooded for at least part of the cropping season. Water depths exceed 100 cm for no more than 10 consecutive days. Crop is transplanted in puddled soil or direct seeded on puddled or ploughed dry soil. During season soil alternates between oxic and anoxic conditions of variable duration and frequency. 

Flood-prone. Distinguished from rainfed lowland rice by extent and duration of flooding. Fields are flooded to at least 100 cm and often much more for at least 10 consecutive days in tiie growing season. Crop is transplanted in puddled soil or direct seeded on ploughed dry soil soil may alternate between oxic and anoxic conditions during season. 

Upland. Grown in level to steeply sloping fields that are rarely flooded. No effort is made to impound water as for other rice ecosystems. Crop is direct seeded on ploughed dry soil or dibbled in wet, non-puddled soil. 

Transport of NH4+ to the roots in Kirk and Solivas experiment was mainly by diffusion. The additional transport resulting from mass flow of soil solution in the transpiration stream would have increased the influx across the roots by about QQaVa/0.5bD% where Va is the water flux (Tinker and Nye, 2000, pp. 146-148), or about 4% in Kirk and Solivas experiment. A sensitivity analysis showed that rates of diffusion will generally not limit uptake in well-puddled soils, but they may greatly limit uptake in puddled soils that have been drained and re-flooded and in unpuddled flooded soils. 

Painuli DK, Woodhead T, Pagliai M. 1988. Effective use of energy and water in rice-soil puddling. Soil and Tillage Research 12 149-161. 

Table 2.1 Effect of puddling on percolation rates in a range of flooded Philippine soils...

Figure 2.1 Changes in water potential with depth in a puddled flooded soil...

The resnlts broadly tally with experimental findings for rice. The maximum length of primary root required to sustain a plant depends on soil conditions and planting density. Typically the depth to the plongh pan in a puddled ricefield is less than 2 dm, and a typical spacing between plant hills is 25 cm x 25 cm... 

Despite the burning of crop residues in the productive, irrigated rice areas of tropical and subtropical Asia, and their removal for other purposes in the low-producing rainfed rice areas, soil carbon levels are largely constant (Bronson et al., 1998). In any case, the amount of carbon in the shallow puddled layer of ricefields amounts to only a few per cent of the amount in natural wetlands. 

Dried Puddles Concentrate Molecules In our common experience, we have all observed the formation of puddles after a rain. We realize, without much analysis, that the puddle is not formed from rain that fell in only that location. It contains water that fell nearby and flowed to that area, which is at the locally lowest elevation. If the rain falls on an area that has buried sources of explosive molecules, then some of those that were sorbed to the surface particles above the source will be dissolved and carried into the puddle. When puddles dry they leave a concentration of molecules on the surface soil particles. Thus, an irregularly shaped area of relatively high concentration of molecules may appear some distance from any buried source. See the discussion on Figure 8.2 p 182. 

Editor You discussed the camouflage patterns of leaked explosives in soil and vegetation. How long after the puddles dry are MDDs able to find the scent It would seem that, since animals must be trained with particular suites of molecules, or aromas, that these should match the expected field aromas. Do decomposition products become more important and change over time ... 

Soils high in montmorillonite possess high CEC and high H20 holding capacity but exhibit slow intake of H20, puddle easily swell and shrink and thus subject to dispersion-flocculation phenomena... 

Most of the composite was applied in 25°-45°F weather with no difficulty. Damp soil, ice, light coverings of snow, and shallow puddles of water presented no serious hindrance to attaining a continuous liner. Bubbles of vaporized moisture were trapped in the initial pass of molten composite, but subsequent layers went down smoothly. 

With very fine textured soils it is advisable to add the initial water with minimum of stirring to avoid puddling. 

Set your vase in a sunny spot and add more blue water each week. Don t over water, because too much water harms many plants. Stop if a puddle forms. Watch to see if your beans and grass grow and in which layer of soil in your Soil Sampler they grew best—clay, sand, or topsoil. 

Cultivation of soils, other than those that are very sandy, is usually injurious to aggregation if the soils are too wet. Under such conditions a partial puddling can occur and the result on drying may be a very compact cloddy, poorly-aerated soil. This bad effect increases as compaction, brought about by heavy machinery, increases. The presence of abundant organic matter markedly decreases any harmful effects of cultivation in practice, its effect is to widen the optimum moisture range at which cultivation can take place without harmful effects. 

The physical condition existing in a loam or clay soil is very dependent on whether past tillage operations were conducted at the proper time - that is, when neither too wet nor too dry. Very sandy soils can be plowed at almost any time but this is not true of the heavier soils they are either too wet or too dry most of the time. If these heavy soils are too dry, tillage is not very effective in making a fine seedbed free of clods. If the soil is too wet, portions of it are puddled, leaving clods when dry. A shiny, slick surface left by the moldboard plow serves as visible evidence that the soil was plowed when too wet. 

The removal of soil by water is due to the energy of the falling raindrop, and to the nearly horizontal movement of the water that flows over the soil surface. Both processes or forces act simultaneously. Under conditions that favor erosion, the amount of soil removed increases as the slope increases. A soil of zero slope would obviously not be eroded, although the impact of raindrops would damage the surface of exposed soil by puddling and sealing it against the entrance of water and air. 

Soils differ widely in their stability or capacity to resist the impact of the falling raindrop. Even those soils that have high resistance to this force are, nevertheless, affected by it, even if at a slower rate. No exposed soils with considerable amounts of clay and silt can completely resist aggregate destruction and puddling that interfere with infiltration and increase erodibility. 

The stubble-mulch system is a variation of the complete mulch system (see Chapter 25). Such a mulch seldom covers all of the soil surface, and hence does not absorb all of the raindrop energy. Nevertheless, it is very effective and, furthermore, helps to retard the movement of flowing water. Obviously, the heavier the preceding crop, the better the soil coverage by the mulch is likely to be, and the greater the erosion protection. Any exposed soil may be puddled, but that under the residues is free to absorb water at a rate little affected by the rain. Many experiments have shown that as little as 700 lb. of straw... 

Continuous puddling of soil in the surface 15-20 cm soil layers creates a hard pan below the plow layer, which is highly compacted and has very low permeability. The hard pan development does not occur in recently developed paddy soils, but in soils that have been under cultivation for several years. 

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