Soil physical quality is essential for plant growth and sustainable agricultural systems. This study aimed to evaluate the efficiency of the least limiting water range (LLWR) to monitor soil compaction and soil physical quality for soybean, without and with irrigation. The study was carried out in an clayer Red Latosol (Oxisol) (21 ° 14 ' 53 " S; 48 ° 17 ' 20 " W; 540 m asl). The experiment was entirely randomized, in a 6 x 2 factorial scheme, with four repetitions. The compaction treatments were: T1 = without compaction; T2 = 1 pass of a 4 t tractor; T3 = 1, T4 = 2, T5 = 4 and T6 = 6 passes of an 11 t tractor over the same track. Soybean (Glycine max (L.) Merrill), cultivar IAC Foscarim 31 was planted. Undisturbed soil samples were collected in the layers 3-6, 8-11, 15-18 and 22-25 cm to determine soil physical attributes. In the harvest soybean yield was evaluated in 3.37 m² microplots. Soybean yield, cultivated without and with irrigation, dropped when penetration resistance increased from 1.30 to 1.64 MPa and bulk density from 1.26 to 1.29 kg dm-3, with yield losses of 19.15 and 11.71% at the highest compaction level (RP = 2.84 MPa; Ds = 1.45 kg dm-3), respectively. The LLWR was reduced by RP until reaching critical soil bulk density (Dsc(IHO = 0)) of 1.33 and 1.38 kg dm-3, in non-irrigated and irrigated soybean. LLWR is an adequate indicator of soil compaction and physical quality for soybean when applied based on the critical bulk density value Dsc(LLWR = 0). Irrigated soybean is more tolerant to compaction.
Glycine max (L.) Merrill; machinery traffic; soil quality; water content
