Maize response to localized mineral or organic NP starter fertilization under different soil tillage methods

An early maize (Zea mays L.) sowing date plays a key role in increasing the grain yield, especially in a temperate climate. The adoption of reduced tillage techniques, such as strip tillage (ST), can decrease cultivation costs, compared to plowing (PLOW), but might also reduce the crop early development rate as a result of lower soil temperatures. Therefore, farmers often adopt starter fertilizations when sowing maize, in order to improve the early-season nutrient uptake, nutrient use efficiency and plant development. The aims of this study were to assess the effects of the adoption of ST, compared to PLOW, and a starter fertilization with deep-injected digestate (DIG) or sub-surface placed diammonium phosphate (DAP), compared to an unfertilized treatment (NT) on the early growth, grain yield and grain qualitative and sanitary traits of maize. Field experiments were carried out in NW Italy over the 2019 and 2020 growing seasons on two different soils. ST determined cooler soil conditions at both sites, compared to PLOW, thus resulting in lower NDVI values due to both slower plant development and lower final crop density. The starter fertilization with DAP recorded the best early vigor and canopy development, expressed as plant height in both sites and for both tillage techniques, while the DIG values were intermediate between the DAP and NT treatments. Although the effects on the early vigor of maize differed between the experimental sites, displaying more pronounced differences in the finer-textured soil, ST on average delayed the flowering (+2.2 days) and consequently delayed the moisture dry down process (+1.2% grain moisture content at harvest), compared to PLOW. The starter fertilization with DIG or DAP led to an earlier flowering, compared to NT (−2.6 and −4.6 days, respectively). The grain yield was not affected by the tillage system, as the plants in ST compensated for the lower plant density with an increased ear length (+1.5%). Instead, DIG and DAP recorded similar and higher grain yields (+1.8 and +1.6 Mg ha−1) than NT. DIG application led to a higher grain protein content and lower level of fumonisin contamination than the other treatments, while ST determined higher deoxynivalenol values than PLOW. The combination of ST and DIG as a starter fertilization can help maintain the production level and the grain quality, compared to conventional techniques that involve the use of mineral fertilizers and plowing, thereby leading to a higher sustainability of the maize cropping system.