Crop responses to soil physical conditions

Abstract

The main soil physical conditions influencing crop growth include temperature, water content, oxygen availability, soil strength of seedbed layer at emergence, and soil below during later growth. Their effects are related to site conditions. For example, in cold climates low seedbed temperatures and/or oxygen deficiency while in hot climates by high temperatures and/or high soil strengths can slow emergence and final stand establishment greatly. An important factor affecting root growth and distribution in tilled soils is vertical and horizontal strength discontinuity. The vertical discontinuity occurs between aggregated seedbed layer and firm soil below and between the plow layer and plow pans. The horizontal discontinuity is mostly caused by a greater strength under machinery tracks. Root response to soil physical conditions depends on the presence and distribution patterns of pores larger than roots that allow bypass the zones of high mechanical impedance and low aeration. When soil physical properties suppress root size, shoot growth and functions are influenced due to root-to-shoot signaling. Main shoot functions include photosynthesis and transpiration that are related to the leaf stomatal diffusive resistance. Usually crop growth is influenced by soil physical characteristics acting in combination and thereby it is often difficult to determine their relative contributions. The soil water status plays a very important role since it affects other significant soil physical factors such as aeration, strength, and temperature. The soil physical conditions are mostly influenced by tillage, compaction, and crop residue management. Further research is needed to explain the perception of soil physical stress by plants and the conversion of physical phenomena into physiological responses.