The effects of crop rotation and fertilization on wheat productivity in the Pampean semiarid region of Argentina. 1. Soil physical and chemical properties

Wheat in the semiarid region of Argentina has often been grown as a low-input crop, Rainfall scarcity and distribution are the main characteristics of this region. The knowledge of the combined effects of crop rotation and fertilization on soil physical and chemical properties are the key for a sustainable crop production. Soil properties for an Entic Haplustoll in the semiarid region of Argentina were evaluated, where differ ent crop rotations were used for 15 years. Wheat-wheat (Triticum aestivum L.) (WW), wheat-grazing natural grasses (WG) and wheat-legume [vetch (Vicia sativa L,) plus oat (Avena sativa L.) or Triticale (Triticum aestivum L. x Secale cereale L,)] (WL) rotations with and without fertilizer (64 kg N and 16 kg P ha(-1)) were studied. The annual wheat cropping system (WW) resulted in the lowest soil organic carbon (SOC) and total nitrogen (N-t) levels. Extractable phosphorus (P-ext) values were sufficient for wheat growth with all treatments and decreased with depth. Fertilizer applications significantly increased the proportion of large pores (>8.81 mu m) in the 0-0.07 m depth of the WW and WG system plots. A decrease in the proportion of medium size pores (0.19-8.81 mu m) and in the water holding capacity was observed in the WG rotation plots. The fertilized treatments resulted in the following sequence of available water: WL > WW > WG, Bulk density was similar with all treatments for each depth, except with the fertilized WG treatment that had the lowest value in the 0-0.07 m depth. These results showed the positive influence of legume inclusion (WL) and alternate cable grazing (WG) on SOC and N-t contents, (C) 2000 Elsevier Science B.V. All rights reserved.