Persistence of Loosened Horizons and Soybean Yield Increases in Bolivia

Abstract

Soil compaction is a major factor limiting soybean [Glycine max (L.) Merr.] production in tropical eastern Bolivia. An experiment was conducted from 1985 through 1989 on a fine‐loamy, siliceous, isohyperthermic Aquic Ustropept with a compacted horizon (0.12–0.33 m) to determine the persistence of subsoil loosening by deep tillage and its effect on soybean yield responses. Four tillage treatments were investigated: conventional tillage consisting of disk harrowing to 0.12‐m depth (CN), subsoiling in 1985 only to 0.40‐m depth (SS/85), disk plowing in 1985 only to 0.30‐m depth (DP/85), and annual subsoiling (SS/YR). All three deep tillage treatments completely loosened the compacted horizon, reducing penetrometer resistance (PR) from a maximum of 3.05 to 2.01 MPa. From December 1987 onward, which coincided with an exceptionally wet period, subsoil reconsolidation occurred, and by June 1989 the PR of CN, DP/85, and SS/85 exceeded 3 MPa. Reconsolidation was attributed to a close‐packing rearrangement of soil particles under wet conditions. Coupled with increasing subsoil strength, a relatively greater reconsolidation occurred in SS/85 and DP/85, resulting in reduced “loosened” zones of 0.07‐m and 0.04‐m thickness, respectively. The pattern of relative reconsolidation suggests it occurred from above downward and from below upward, the latter perhaps being related to a high water table. In contrast SS/YR maintained a much thicker “loosened” horizon. overall subsoil reconsolidation, soybean yield responses continued for 3 yr with SS/85, and for 4 yr with DP/85 and SS/YR. Although substantial differences in relative reconsolidation existed between DP/85, SS/85, and SS/YR, few significant differences in yield were found when soil water was limiting.

Soil compaction by machine traffic and least limiting water range related to soybean yield

“…However, these limiting values must be analyzed with caution, when decisions should be taken about physical or biological actions to increase soil loosening. In imperfectly drained tropical soil in Bolivia, it was noticed that soybean yield (cultivar IAC 8) decreased at PR values from 2 to 3 MPa, determined at water content equal to FC, with smaller values in years with more rainfall, as a consequence of reduction in internal drainage and aeration deficiency in compacted soil (Barber, 1994).…”

“…However, Barber (1994), Flowers & Lal (1998) and Czyz (2004) emphasized that changes in limiting values of PR and D b were a function of water content. These observations were related to an experimental area location, which favors good internal drainage, with few aeration deficiencies, in irrigated cultivation.…”

“…In the present study, we can infer that a small amount of aeration deficiency occurred with the occurrence of the same D b limiting levels with and without irrigation. Aeration deficiency is widely reported in poorly drained soils, in which PR and D b limiting to yield is smaller, in years with high rainfall amount, compared to dryer years (Barber, 1994;Czyz, 2004). This way, benefits of lower PR in irrigated cultivation were possibly minimized by poor aeration, compared to cultivations without irrigation, related to limiting values.…”

Improvement of a testing apparatus for dynamometry: procedures for penetrometry and influence of strain rate to quantify the tensile strength of soil aggregates

“…Soil penetration resistance (PR) is often used as soil quality indicator, to characterize compaction and mechanical limitations of root growth (Barber, 1994) as well as the effects of tillage (Busscher et al 2000) and machinery traffic (Sharratt et al, 1998). Letey (1985) argues that PR is a soil physical property that influences plant growth directly and hence crop yield (Kirkegaard et al 1995;Beutler et al, 2006).…”

In-Row Subsoilers that Reduce Soil Compaction and Residue Disturbance

“…To achieve maximum benefits common practice and provides additional soil from these crop residues, they must be left on the soil surface volume for expansion of plant roots (Box and where crop residues can intercept rain drops and prevent soil Langdale, 1984;Busscher and Sojka, 1987;Bus-erosion (Laflen and Colvin, 1980;Cogo et al, 1984;Dickey scher et al, 1988;Bernier et al, 1989;Barber, 1994;Raper et al, 1984;Blough et al, 1990). Increased infiltration and et al, 1998).…”