Modern Wheat Varieties as a Driver of the Degradation of Spanish Rainfed Mediterranean Agroecosystems throughout the 20th Century

Abstract

The high grain yield of modern varieties (MV) respond to the increase in fossil-based inputs, and the widespread belief that they are more productive than old varieties (OV) is biased. This belief focuses only on marketable biomass, without considering the consequences on agroecosystem sustainability of the reductions in other portions of NPP. Additionally, field comparisons of OV and MV were normally conducted under industrialized farming conditions, which is detrimental for OV performance. Both trials carried out in this study comparing wheat OV and MV show that, under Mediterranean rainfed conditions and traditional organic management, aerial and belowground biomass production of OV is higher than that of MV, without significantly decreasing yield and enabling a better competition against weeds. From the data of our trials, bibliographic review and information from historical sources, we have reconstructed the NPP and destinations of biomass of Spanish wheat fields (1900–2000). Varietal replacement entailed the reduction in residues and unharvested biomass (UhB), which involved soil degradation in rainfed cereal fields and undermining heterotrophic trophic webs. Our results suggest that OV can increase the sustainability of rainfed Mediterranean agroecosystems at present through the improvement of soil quality, the reduction of herbicides use, and the recovery of biodiversity.

Yield and Quality Performance of Traditional and Improved Bread and Durum Wheat Varieties under Two Conservation Tillage Systems

“…All these beneficial effects of plant biomass under conservation agriculture systems are, however, constrained when the crop cultivar shows a genotype-dependent limited vegetative growth. The higher biomass production that characterizes landraces (this study; [1,56,57]) not only helps crop plants compete better with weeds, thus reducing herbicide applications, but also enhances the quality of degraded rainfed soils, clearly being advantageous for sustainable agroecosystems [1,58]. Among the landraces examined in the study, Aragon-03 and Jerez-36 can again be highlighted as good genotypes under either moderate or severe dry conditions.…”

“…However, their advantages over commercial varieties have been described for some yield-related traits that have been identified as potential targets to achieve better grain yields under soil conservation management such as TKW, GFR, biomass production and tillering ability [11]. The high variability for these traits reported in Mediterranean landraces (e.g., [1,15,16]) supports the potential of landraces to improve variety adaptation to conservation agriculture. Further research is then strongly recommended to evaluate more diversified landrace in order to select the most adapted to sustainable agriculture practices under different environments.…”

“…With degraded soils and unpredictable weather patterns, return on investment is uncertain, which increases the economic and social risks for farmers. Under such conditions, one approach to improve crop production, while minimizing soil and other natural resources degradation, is to adopt crop-nutrient-water-land management practices that are collectively included in the term 'conservation agriculture' [1]. The practice is not only effective in enhancing varieties in conservation agroecosystems.…”

Green revolution ‘stumbles’ in a dry environment: Dwarf wheat with Rht genes fails to produce higher grain yield than taller plants under drought

“…In contrast to the tall older cultivars, the best performance of semidwarf modern varieties is achieved via industrialized methods of wheat production, with greater consumption of water and the application of high levels of nitrogen fertilizer. This raises 'valid criticisms' (Evenson & Gollin, 2003) regarding the additional demands on water supplies, particularly in arid and semi-arid areas, as well as the accumulation of chemical pollutants in the soil and nearby aquatic environments due to fertilizer over-application or run-off (Carranza-Gallego et al, 2018).…”

“…Additionally, an obvious conflict exists for industrialized semi-dwarf wheat grown in 'Organic' agriculture, where no artificial inputs are used (Addisu et al, 2010;Carranza-Gallego et al, 2018). These combined agro-ecological concerns could seemingly be resolved through simply not providing the additional water and fertilizer.…”