Subsurface Compaction Effects on Tillering and Nitrogen Accumulation in Wheat

Abstract

AbstractCompaction in the 0.05‐ to 0.30‐m depth may limit tillering and N accumulation in wheat (Triticum aestivum L.); these effects may be yield reducing. Before imposing compaction treatments in a field study in Minnesota, perforated small‐diameter tubing was buried in a Waukegan silt loam (sandy skeletal, mixed, mesic Typic Hapludoll) at a depth of 0.2 m in all plots. Compacted plots each received four passes with a heavy vibrating roller, while control plots were disk plowed and then disk harrowed. All plots were then surface roto‐tilled and seeded to wheat. At early tillering a K15NO3 solution was applied to the subsurface via the tubing. Plants sampled for 15N/N recovery 24 h after 15N application, at anthesis, and at maturity showed no significantly different 15N or N concentration or accumulation per culm/ individual organ in response to compaction. Because subsurface compaction reduced tillering, N uptake in the grain and straw was reduced by 21 and 30%, respectively. After the 0.10‐m surface layer was removed from all plots in a field study on a clay loam soil (Typic Calcixerolls) in Morocco, the subsurface was compacted by four passes with a 7.5‐ton tractor. Soil was then replaced, leveled, and only the control plots were disk plowed and disk harrowed twice. Both compacted and control plots were roto‐tilled and seeded. Nitrogen concentration and accumulation per culm/individual organ immediately after tillering was reduced less than 5% by the compacted treatment in both 1982 and 1983. Reduced tillering in the compacted treatment reduced average N uptake 11 and 28% in the grain and straw, respectively. In all three tests N concentration in the shoot at the end of tillering was high; yet it was higher in the compacted treatment. Then N concentration and uptake was reduced by compaction on a per culm basis at maturity, and earlier in one of the field studies. Root length density was reduced in the compacted zone in response to greater penetrometer load and higher bulk density. Tiller bud development was suppressed by the compaction treatment as much as 20% even though concentrations of N were high in the shoot. Tiller losses and declines of N concentration in the shoot in the post tillering stages were nearly the same in both treatments. Additional N before tillering therefore cannot overcome the adverse influence of subsoil compaction.