Differences in Sensitivity of Natural Vegetation and Rainfed Crops to Soil Texture across Biomes and Scales

Abstract:

The sensitivity of rainfed crops to soil texture guides many agronomic operations (timing, crop selection, inputs), particularly in water-limited regions. Unlike annual and mono-cultured crops, natural vegetation undergoes continuous selection of traits and species to better adapt to local soil and climatic conditions. In the process of this adaptation, we hypothesize that natural vegetation becomes insensitive to soil texture; in contrast, crop response to rainfall anomalies is accentuated or diminished by local soil texture. We use field observations and remote sensing data to systematically examine the responses of natural and rainfed cropped vegetation to rainfall anomalies across biomes and scales. At local scales (0.1 km), we use crop productivity from literature data (crop yields) and natural vegetation productivity as Gross Primary Productivity (GPP) from FLUXNET sites. At regional scales, we rely on remote sensing-based GPP. Results confirm a lack of response of natural vegetation productivity (GPP) to soil texture across biomes and rainfall anomalies at all scales, whereas crop yields at local scale show correlation with soil texture in dry years (in agreement with conventional agronomic practices). The correlation of crops with soil texture vanishes at larger scales (250 x 250 km) using remotely sensed GPP. Resampling the same remote sensing scenes at smaller scales (25 x 25 km) shows sensitivity of crop GPP to soil texture in dry years. Results suggest that natural vegetation is adapted to local climatic conditions with stabilized soil structure that alleviates soil texture limitations, whereas rainfed crops retain dependency on soil texture that is clearly manifested at local scales but is obscured at larger scales by topography, aspect, and uncertainty in soil and GPP maps. The study (i) provides new insights into what natural vegetation’s climatic equilibrium might mean, (ii) highlights the potential of cumulative structural alterations that diminish soil texture influence relative to cropped fields, (iii) postulates different water stress functions for crops and natural vegetation, and (iv) reveals the role of scale in expressing such sensitivities in Earth system models.