Julio O. Iglesias

The effects of crop rotation and fertilization on wheat productivity in the Pampean semiarid region of Argentina: 2. Nutrient balance, yield and grain quality

Wheat (Triticum aestivum L.) in the semiarid region of Argentina has often been grown as a low-input crop. Rainfall scarcity and distribution are the main characteristics of the region. Consequently, a knowledge of the effect of different management practices is the key to sustainable crop production. The objective of this work was to study the effect of 15 years of different wheat management practices on plant nutrition, dry matter production and grain yield and quality. The treatments were: continuous wheat (WW), wheat-grazing natural grasses (WG) and wheat‐legume: [vetch (Vicia sativa L.) plus oat (Avena sativa L.) or Triticale (Triticum aestivum L. Secale cereale L.)] (WL), with and without fertilizer (Na P) application. The WW and WL treatments involved annual tillage and a long fallow period (4‐6 months) under stubble mulch, and WG involved annual alternate tillage and a short fallow (1 month). The experiment was started in 1975 and the data presented were obtained in 1989. Wheat yields were higher with the WW than with the WG rotation, but in both rotations fertilization was required to obtain better grain quality (protein content higher than 11 per cent). The wheat‐legume rotation resulted in the highest yield, protein content, and better yield components. Fertilizer application did not increase dry matter production but improved nutrient uptake and grain quality. Yield component differences could be attributed to water availability due to different fallow length. The wheat‐legume rotation seemed to be the best practice in the semiarid Pampean region. # 2000 Elsevier Science B.V. All rights reserved.

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 different 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. Secale cereale L.)] (WL) rotations with and without fertilizer (64 kg N and 16 kg P ha ˇ1 ) were studied. The annual wheat cropping system (WW) resulted in the lowest soil organic carbon (SOC) and total nitrogen (Nt) levels. Extractable phosphorus (Pext) values were sufficient for wheat growth with all treatments and decreased with depth. Fertilizer applications significantly increased the proportion of large pores (>8.81 mm) 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 mm) 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 cattle grazing (WG) on SOC and Nt contents. # 2000 Elsevier Science B.V. All rights reserved.

Continuous Wheat in Semiarid Regions: Long-term Effects on Stock and Quality of Soil Organic Carbon

Abstract Continuous wheat (Triticum aestivum L.) cropping in semiarid regions results in variable dry matter production. As a consequence, the balance of soil organic carbon (SOC) may vary across time. The aim of this research was to assess the dynamics and long-term changes of physically and chemically extracted SOC fractions. Soil samples (0- to 5-, 5- to 10-, and 10- to 20-cm depths) from continuous wheat with (f) and without (nf) fertilizer (N + P) under conventional tillage ((CT) for 25 years) and no-tillage ((NT) for 6 years) were taken during the experiment. Mineral-associated ((MOC) 0–0.053 mm), fine particulate ((POCf) 0.053–0.100 mm), and coarse particulate ((POCc) 0.1–2.0 mm) SOC and humic substances were obtained. The SOC variability depended on water availability during fallow periods (SOC decomposition) or crop cycles (dry matter production). The mean wheat yields were 1.33 (nf) and 2.09 (f) Mg grain ha−1, with an estimated carbon input of 1.64 (nf) and 2.20 (f) Mg C ha−1 year−1. Losses from the initial level were higher in labile fractions, POCc (−75%) and POCf (−53%), than in MOC (−15%). Humic acids present slight differences in their structure and quantity as a result of long-term cropping. Conversion from CT to NT resulted in contrasting results. For an equivalent soil mass, fertilizer application increased SOC by 4.31 Mg ha−1 (under CT) and 7.29 Mg ha−1 (under NT). The SOC turned out to be higher under NT with fertilizer use and lower without application. No-tillage does not increase SOC content by itself; it must be combined with other agricultural practices such as fertilization and/or crop rotation.