Effect of hairy vetch cover crop on maize nitrogen supply and productivity at varying yield environments in Southern Brazil.

Cover crops play a critical role on conservation and sustainable agriculture due to their well-documented benefits on both soil and crop productivity. Inclusion of legumes (e.g., hairy vetch, Vicia villosa Roth) in the farming system can reduce the nitrogen (N) fertilizer needs for cereals such as maize (Zea mays L.) crop while maintaining or increasing its productivity. The aims of this research study were to quantify the effect of hairy vetch as a cover crop on: i) successor maize yield under varying yield environments (YEs) and fertilizer N rates, and ii) maize N status [N uptake, N nutritional index (NNI), and N fertilizer replacement value (NFRV)] at flowering time. Two field studies were carried out in Southern Brazil under varying YEs. The factors investigated were: YE (low, medium, and high), hairy vetch cover crop (with and without), and fertilizer N rate (0, 60, 120, 180, and 240 kg N ha-1). Under the combination of low YE and low fertilizer N rates (0-60 kg ha-1) with previous vetch, maize displayed the largest yield response and an improvement in its N status. The NNI determined at maize flowering was an efficient index of the vetch effect, increasing delta maize yield response (yield with- minus without-vetch) as the NNI reduced, with more than 10% delta yield response with NNI below 0.85. The NFRV of the hairy vetch represents potential N savings of 151 kg N ha-1 for the LYE, 95 kg N ha-1 for the MYE and from 59 to 45 kg N ha-1 for the HYE depending on the tested fertilizer N rate. The N coming from the legume cover crop in addition to the N fertilization was critical for supplying N to maize and boosting productivity across all YEs.

Conversion from mineral fertilisation to MSW compost use: Nitrogen fertiliser value in continuous maize and test on crop rotation.

The recycling of agricultural wastes, co-products, and by-products is necessary for creating circular economic (closed loop) agro-food chains and more sustainable agro-ecosystems. The substitution of N mineral fertilisers with recycled organic fertiliser promotes a circular economy, makes the agricultural system more environmentally sustainable, and guarantees food security. Results from a continuous maize experiment and four-year rotation cropping systems (maize, winter wheat, maize, and soybean) were used in a three-year study that replaced part or all mineral fertilisers with Municipal Solid Waste Compost (MSWC). In the first experiment, two different fertilisation strategies, MSWC only (M-Com) and mineral fertilisers (M-Min), were compared with zero nutrients (M-Test 0), whereas in the rotation cropping systems, mineral fertilisation (R-Min) was compared with a combination of MSWC and mineral fertilisers (R-Com + Min). Depressed yields resulted in the initial year of compost application, but by the middle term (three years), MSWC fertilisation showed a good N fertiliser value, mainly for yield summer crops and integrated with N mineral fertilisers. Different soil indicators and the N content in crop tissues and soil suggested that the scarce N availability recorded mainly during the first year is responsible for yield reduction. Due to limited supplies of MSWC, soil total N and the stable organic fraction bound tightly to minerals (MOM), did not vary significantly in the three-year experiment. Conversely, the more labile organic fraction (fPOM) increased only in the top soil layers (0-15 cm). Also in the top layer, M-Com increased the amount of organic fraction occluded into soil aggregates (oPOM). Furthermore, replacement of N mineral fertiliser with compost effectively mitigated N2O emissions in wheat and maize. Overall, the fertiliser value of MSWC was maximised when it was used repeatedly and in combination with mineral fertiliser, especially in spring and summer crops.