Integrated hole-sowing, fertilization, and plastic mulching techniques are common agronomic practices applied to collect rainwater and to improve rainwater utilization in semiarid rain-fed regions. However, little is known about the growth responses of tartary buckwheat (Fagopyrum tataricum L.) to the practices adopted in semiarid areas of Loess Plateau in Northwest China. To address the concerns, a long-term field experiment was conducted in 2015–2017. Four fertilization levels, namely, high fertilization level (N–P2O5–K2O: 120–90–60 kg ha−1, HF), moderate fertilization level (80–60–40 kg ha−1, MF), low fertilization level (40–30–20 kg ha−1, LF), and zero fertilization level (ZF), were applied to hole-sown tartary buckwheat with whole plastic mulching, in comparison to the control with no-mulching and zero fertilization (CK). Several key growth-influencing indicators were measured in the consecutive experimental years, including soil temperature (Ts), soil water storage (SWS), leaf area index (LAI), dry matter (DM), and grain yield. The results showed that in different precipitation years, 2015 (193 ± 23 mm), 2016 (149 ± 19 mm), and 2017 (243 ± 28 mm), the ZF, LF, MF, and HF treatments had the potential to optimize Ts in 0~25 cm soil layers (at 5 cm interval). The four treatments improved SWS in 0~300 cm soil layers by 3.5% and increased soil water consumption in the pre-anthesis period by 22.4%, compared with CK. Moreover, the four treatments shortened the pre-anthesis growth period by 0.4~5.4 d, while extended the post-anthesis growth period by 5.7~10.0 d, giving rise to an overall extension of 0.6~5.0 d for a whole growth period of tartary buckwheat. Furthermore, the ZF, LF, MF, and HF treatments increased LAI by 4.4~225.3% and DM weight by 41.5~238.0%. The rain yield of the four treatments was increased by 14.0~130.4%, and water use efficiency (WUE) was improved by 11.3~102.7%, especially for the LF treatment, compared with CK. The study indicated that the technique of hole-sowing and plastic mulching combined with a low fertilization rate was an effective measure for tartary buckwheat to optimize crop growth and to boost grain yield and WUE on semiarid lands.
