Changes in soil-plant-water relationships and crop yield under conservation agricultural practices

Conservation agriculture is a farming system based on three main principles: reduced soil disturbance, permanent organic cover, and crop rotation. It is widely promoted as a sustainable solution to reduce soil degradation, restore and maintain soil health, enhance climate resilience in crop production, and mitigate greenhouse gas emissions. However, its universal applicability across diverse biophysical and socioeconomic contexts remains highly debated due to inconsistent agronomic performance. Using a global meta-analysis, we evaluated the effect of conservation practices under different climate and soil conditions on soil properties that regulate soil-water movement, storage, accessibility to crops, soil aeration, and crop yield. Performances of five conservation agricultural practices, namely no-till without residue (NT), reduced tillage without residue (RT), no-till with residue (NT+RR), reduced tillage with residue (RT+RR), and conventional tillage with residue retention (CT+RR), were compared with conventional tillage without residue (CT) based on observations from 328 studies across 361 experimental sites.

Mean yield responses to conservation practices ranged from a reduction of 6.3% (p=0.02) for NT to no significant yield effects (+3.4%; p=0.29) under CT+RR as compared to CT. Increasing tillage intensity (from NT to CT) and residue retention were associated with higher crop yields (p=0.046). Yield outcomes varied with climatic and soil conditions. In semi-dry climates (aridity index: 0.3-0.65) NT increased yields by 16.3% (p=0.004), likely related to changes in infiltration (+24%, p=0.12), although the mean change was not significant for the latter. In contrast, NT reduced yields in humid climates (-7.2%, p<0.001) and in dry regions, where irrigated agriculture was expected to dominate (8.9%, p=0.031). The largest yield reductions occurred in clayey soils (NT -22.2%, p=0.07 and RT -25.8%, p = 0.004), whereas the smallest reductions and occasional gains were observed in sandy soils, which also aligns with a significant trend in infiltration responses (p=0.007), ranging from a mean reduction of 26% (p=0.15) in clayey to a mean increase of 21% (p=0.16) in sandy soils.

Sensitivity analysis revealed that crop yield under NT is strongly influenced by bulk density, possibly due to its cascading effects on soil hydraulic and mechanical properties that regulate water availability, air circulation, root growth, and thus crop-water and nutrient uptake. Although bulk density increased only non-significantly by 5.4% under NT, this was accompanied by 40% (p<0.001) increase in penetration resistance, 18.6% (p<0.001) reduction in air-filled porosity, and overall increase in plant-unavailable water capacity (wilting point). We conclude that while NT and RT can enhance infiltration and soil moisture, crops benefit minimally from these improvements due to a simultaneous soil compaction that 1) hinders root penetration, 2) decreases available water, and 3) limits soil aeration.