Long-term Impact of No Tillage in Two Intensified Crop Rotations on Different Soil Organic Matter Fractions in Argentine Rolling Pampa

A Irizar

doi:10.2174/1874331501307010022

Abstract

It is expected that the agricultural intensification occurred in recent decades in the Argentine Rolling Pampa significantly alters the SOM reserves. Therefore, it is necessary to identify soil organic carbon (C) and nitrogen (N) frac- tions to understand the functionality and stabilization of these reserves. Our objectives were to study the NT effect in two crop rotations, corn-double cropped wheat/soybean (MWS) and double cropped wheat/soybean (WS) on: 1) SOM and its particle size and biological fractions contents, 2) C and N stubble biomass and 3) some soil properties in order to explain the SOM differences found. The larger biomass residue remaining on the soil surface under NT promoted higher aggregate stability and lower soil temperature and pH. At 0-5 cm soil depth, NT exhibited higher C and N contents, for both uncomplexed and intimately associated to the mineral components fractions. However, the results indicated variations in the SOM protection according to the rotation: in MWS the high aggregate stability showed better physical protection, while in WS the greater cation exchange capacity and the lower value of N released by anaerobic incubation would indicate the presence of transformed SOM. At 5-20 cm soil depth, only in WS, C microbial biomass was higher with a low metabolic rate, indicating again the presence of highly decomposed SOM. The results obtained in WS under NT would indicate the possibility of achieving slower recycled of the SOM.

Highlights

One of the main agronomic challenges in degraded agroecosystems is to find crop systems that maintain or increase the reserves of soil organic matter (SOM), to contribute to the mitigation of the greenhouse effect, enable progress in food security and improve the environment.In the Rolling Pampa, the most important cropping region of Argentina, important changes took place in the production systems during the 1970s: the agriculture cycles, which traditionally alternated with pasture cycles, began to be transformed into continuous agriculture
The tillage systems had no significant effects on bulk density (BD) in any of the depths analyzed
The concentrations of Soil organic C (SOC) and soil organic N (SON) were higher under NT than under chisel plow (CP) in the maize-double cropped wheat/soybean rotation (MWS) and WS at 0-5 cm, but not in the others depths (Table 1)

Summary

Introduction

One of the main agronomic challenges in degraded agroecosystems is to find crop systems that maintain or increase the reserves of soil organic matter (SOM), to contribute to the mitigation of the greenhouse effect, enable progress in food security and improve the environment. In the Rolling Pampa, the most important cropping region of Argentina, important changes took place in the production systems during the 1970s: the agriculture cycles, which traditionally alternated with pasture cycles, began to be transformed into continuous agriculture. The relationship between the cultivated surface and the surface with pastures decreased at about 4% annually [1]. Soybean was introduced as a single annual crop or as a double crop accompanying wheat and the work of the soil was intensified: primary work was carried out with moldboard plow and plow up to about 20 cm deep. Towards the end of the 1980s, the soils of this region had already suffered the loss of 40-60% of the topsoil SOM [2].

Objectives

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Discussion

Conclusion