Effect of cultural precedent on a cover culture

Abstract

Cover crops (CC), installed between two main crops (CP), contribute to the sustainability of agricultural activity. They mitigate the leaching of nutrients, namely nitrogen in the form of nitrate, stimulate the soil microbiome, protect the soil from erosion, contribute to the control of certain weeds, and can produce forage material for animal feed; they are sinks of greenhouse gases (GHG). In Portugal, several works have been carried out to assess the impact of CC on the main crop (PC); however, CP assessment work in CC is practically non-existent, especially in a situation of cultural rotation. This work aimed to quantify the impact of 4 crops (corn, industrial tomatoes, butternuts, black-eyed peas ) in a CC, intercropping of grasses and legumes. In 2023, an experimental field was installed at the Escola Superior Agrária de Santarém (ESAS). At 139 days after sowing (DAS), 3 samples were taken from each of the four leaves of the rotation and the distribution of dry matter (DM) of three groups of plants (clovers, ryegrass, and other plants) of the intercrop was evaluated. The total production of dry matter in each of the leaves was also determined, at 146 DAS, the content of N, P, K, Ca, and Mg in DM was determined and the returns to the soil of these nutrients in organic form were estimated. Cultural precedent influenced the percentage distribution of DM across the 3 plant groups. There was a distribution of 60% of DM in the group of other plants in F1 (Black-eyed peas) and F3 (Industrial tomato), while clovers represented around 54% in F2 (“butternuts”) and 52% in F3 (Corn). Total DM production was slightly higher in F3 (5043kg/ha) followed by F2 (4833kg/ha) and F1 (4755kg/ha) and finally F4 (4462kg/ha). However, the differences were not statistically significant (p>0.05). It was estimated that CC returns, on average, in organic form and considering only the aerial part, 77 to 93 kg/ha of N; 11 to 13kg/ha of P; 101 to 141kg/ha of K; 20 to 28kg/ha of Ca and 11 to 13kg/ha of Mg.