Relationship between tillage intensity and initial growth of loblolly pine seedlingsThis article is part of a larger document. View the larger document here.
To determine the relationship between changes in soil attributes associated with differing tillage intensities and growth of loblolly pine seedlings, we measured soil moisture, nitrogen (N) availability, and soil strength across a range of tillage treatments on an Orangeburg soil series near Cuthbert, GA (four replications). We then correlated these measurements to the growth of individual seedlings. The five tillage treatments were: no-till (NT), coulter only (C), coulter + subsoil (CS), coulter + bed (CB), and coulter + bed + subsoil (CSB). Adjacent to 3 trees per plot (60 trees total), soil moisture was measured every 2 weeks using TDR, soil N availability was measured monthly by KCl extractions, and soil strength was measured 2 times during the year using a cone penetrometer beginning in May, 2003. In December of 2003, the 60 trees were excavated to determine tree biomass. Average soil moisture in the upper 60 cm decreased from 28 percent in the NT treatment to 22 percent in the CB and CSB treatments. Nitrate concentrations increased by 33 percent in the bedded treatments (CB and CSB) compared to the NT, C, and CS treatments. From 0 to 200 mm, bedding decreased the average soil strength by 46 percent compared to the other treatments. Subsoiling decreased soil strength at depths > 200 mm. Tillage positively affected relative height growth (p = 0.0005), and all the tillage treatments increased relative height growth compared to the NT treatment. Soil strength between 0 and 100 mm (P=0.002, r2=0.41) was positively correlated with seedling relative height growth. Soil moisture from 0 to 300 mm (P=0.0016, r2=0.44) was negatively correlated with seedling relative height growth. In contrast, N availability was not correlated to seedling growth. These results indicate tillage increases rootability by decreasing soil strength and increasing porosity, and that these changes are associated with increased seedling growth.