Internet of Things (IoT) is shaping the agricultural industry to enhance process control, boost business efficiency, and improve product quality. Digital agriculture has the potential to fulfill the climate change adaptation with optimized natural resources use and achieve economic benefits through increased agricultural productivity. Field monitoring and agricultural processes automation can lead to alternative options for managing natural resources and environment. In addition, social and cultural benefits can be fostered by means of enhanced communication infrastructure. The agriculture domain usually requires long-range communications, extended battery lifetime, and high reliability of sensors devices. Narrowband IoT (NB-IoT) is growing as a key Low-Power Wide-Area Network (LPWAN) technology for IoT applications. Smart Agriculture proves a natural use of NB-IoT, as a typical industrial IoT application. In this paper, a NB-IoT agricultural field test is reported, within a real system architecture, comparing its network performances with General Packet Radio Service (GPRS) standard. The experimental campaign exposes gains and challenges of the technology highlighting the most attractive aspects for the farming context.