Precision sensing through IoT plays an integral role at various stages of crop cultivation to measure the ambient environment and take appropriate action to maximise yield. For IoT to become pervasive, deployments on the farm have to overcome multiple limitations around cost, connectivity, and flexibility. The solutions have to be affordable to justify their value, be transparent to flaky connectivity in remote areas, and suit the sensing modalities associated with different crops. We have developed a portable IoT platform on the edge involving a mobile and a configurable sensor node, which allows us to locally address contextually relevant sensing needs of the farmer. Integrated with a digital farming platform on the cloud, our edge platform helps us to effectively create machine learning based solutions for the farmers in poor connectivity and computing environments. We showcase a case study where our platform interfaced with a soil moisture sensor is used to optimise the use of water.