  In contrast to the rapid digitalization of several industries, agriculture
suffers from low adoption of smart farming tools. While AI-driven digital
agriculture tools can offer high-performing predictive functionalities, they
lack tangible quantitative evidence on their benefits to the farmers. Field
experiments can derive such evidence, but are often costly, time consuming and
hence limited in scope and scale of application. To this end, we propose an
observational causal inference framework for the empirical evaluation of the
impact of digital tools on target farm performance indicators (e.g., yield in
this case). This way, we can increase farmers' trust via enhancing the
transparency of the digital agriculture market and accelerate the adoption of
technologies that aim to secure farmer income resilience and global
agricultural sustainability. As a case study, we designed and implemented a
recommendation system for the optimal sowing time of cotton based on numerical
weather predictions, which was used by a farmers' cooperative during the
growing season of 2021. We then leverage agricultural knowledge, collected
yield data, and environmental information to develop a causal graph of the farm
system. Using the back-door criterion, we identify the impact of sowing
recommendations on the yield and subsequently estimate it using linear
regression, matching, inverse propensity score weighting and meta-learners. The
results reveal that a field sown according to our recommendations exhibited a
statistically significant yield increase that ranged from 12% to 17%, depending
on the method. The effect estimates were robust, as indicated by the agreement
among the estimation methods and four successful refutation tests. We argue
that this approach can be implemented for decision support systems of other
fields, extending their evaluation beyond a performance assessment of internal
functionalities.
