The Ideal Soil: III. Fitness of Edaphic Variables to Achieve Sustenance in Agroecosystems

Abstract

ABSTRACT In the agroecosystems, the soil plays a leading role in establishing systems of sustainable agriculture. Therefore, edaphic attributes related to functions that soil renders to crops have been proposed as potentially useful to infer whether those functions are suitable to diagnose or the adopted management system led to sustainability. Those attributes are: Bulk density (Bd); Macroporosity (MPo); Optimal Hydric Interval (OHI); Aggregates stability (As); Relative Aggregates stability (rAs); Rooting depth (Rd); pH; Available Phosphorus (P); Active Nitrogen (acN); and Seal Infiltration (Iseal). The potential fitness of some of those attributes, linked with functions that soils must render to crops, is studied here. All the studied lots are located in Argiudolls, in the Province of Santa Fe, in Reconquista (NE), Hipatia (center-east) and San Jorge (center-west). The variation in the value of the attributes in different soils, which are exposed to contrasting management systems, is analysed. These contrasting management systems are: (a) Never cultivated (Nat); (b) With more than 20 years of conventional till (C-till); (c) In agriculture/artificial prairie rotation (R); and (d) Cultivated for several years in direct drill (DD). Later those values are compared with their critical threshold (CT) values based on regional experience and on specific bibliography. The most sensible variables have been OHI, Iseal, P, acN and pH. C-till causes degradation of all the measured attributes, taking the soils far from their natural states and therefore from the Ideal Soil, while on the other hand, DD causes less soil degradation: After 6 years of DD practice only Mpo, Bd and rAs, in some cases, reached the Ideal Soil values. The use of the Ideal Soil concept to assess and detect the CTs of the main attributes may guide scientific research as much as the agricultural practices to improve unfavorable soil properties. However, when scanning the fit attributes and knowing their CT values, only a qualitative or half-quantitative agronomic judgment can be made. In order to do that, the diverse attributes must be integrated in a mathematical, dynamic model, which simulates the multiple interactions that occur among soils, atmosphere and crops in the North Pampean Region. This evolves to complement the analytic-reductionist approach that has guided this research, with the holistic and systemic one.