Wet soil and Compaction
Hi Hope Sandra can clarify this but for 3b I think that water applies so sort of 'stress' to the soil and with machinery weight the soil will exceed its stress-bearing capacity and deform... and so driving tractors on dry soil to might be a better alternative
I'm also wondering for 3a), would only structure be affected by compacting (because pores collapses) but it wouldn't affect the texture(because texture = proportion of sand silt and clay sized particles but this has nothing to do with compaction)?
Compaction:
Wanyue, see lecture #7 - soil consistency. As soil moisture content increases, the soil's bearing strength drops. As moisture content increases, the soil consistency moves from plastic limit (can be molded and does not crumble under stress) to liquid limit (where the soil tends to flow with the application of stress).
Think back to lab #2, hand texturing. You took a dry soil, added a little water and the consistency changed; you could shape and "compact" that sample.
Melody, regarding question 3b) on the 2018 midterm - you are correct re: when to utilize machinery. See lecture #11 (soil water terms), slide 10 "Field capacity is near the plastic limit = the optimal wetness for tillage or excavation" i.e. use of heavy machinery.
For 3a) effect of compaction on texture versus structure - you are correct, think of the definition of texture: proportion of inorganic mineral particles in the sand, silt and clay size fractions, which is not impacted by heavy machinery.