Title : Cover crops improve soil biological activity, phosphorus availability and carbon sequestration
Abstract:
Cover crops have the potential to modify soil structure and access phosphorus (P) reservoirs, altering P fractions and increasing P availability for cash crops. The search for mechanisms capable of reducing P adsorption is essential, as these strategies may also decrease the dependence on phosphate fertilizers, a finite and limited resource. Therefore, this study aimed to evaluate the effects of cover crops on soil enzymatic activity and their implications for biomass production and soil carbon stocks. The experiment was established in a randomized complete block design with eight treatments and three replications. Treatments consisted of six cover crop species (common vetch, white lupin, forage radish, ryegrass, black oat, and rye), one fallow treatment with frequent desiccation of spontaneous vegetation, all receiving soluble phosphate fertilization (single superphosphate), and an additional fallow treatment without phosphate fertilizer application. Data were subjected to analysis of variance, and means were compared using the Scott-Knott test (p ≤ 0.05). Dunnett’s test was also applied to compare the treatment without P fertilization against the other treatments. After 12 growing seasons, comprising seven years of phosphorus input into the system and five years of residual P exploitation, black oat showed the highest biomass production, reaching 46.64 and 29.47 t ha?¹ of dry matter under the two respective scenarios. Under continuous P input, the highest P accumulation was observed in forage radish (187.03 kg ha?¹ P) and black oat (160.60 kg ha?¹ P). Under residual P conditions, black oat remained among the highest accumulators (129.75 kg ha?¹ P), together with rye (127.87 kg ha?¹ P). Regarding acid phosphatase activity in the 0–5 cm soil layer, white lupin exhibited the highest enzymatic activity, reaching 1,832.94 μg p-nitrophenol g?¹ soil h?¹, representing an increase of approximately 58% compared with the fallow treatment (1,058.43 μg p-nitrophenol g?¹ soil h?¹). Microbial P was also highest under white lupin (12.0 mg kg?¹ P), although it did not differ significantly from the fallow treatment. For soil carbon stocks, forage radish, black oat, and common vetch outperformed the other treatments, with averages of 105, 101, and 101 Mg ha?¹ C, respectively. These values corresponded to increases of 14%, 10%, and 10.5% relative to the fertilized fallow treatment (90.3 Mg ha?¹ C). Among the evaluated cover crops, black oat and white lupin showed the most favorable performance regarding both soil carbon stock enhancement and phosphorus availability. Overall, the results indicate that greater phosphorus availability within the system contributes to increased soil organic carbon accumulation.
