Humic amendment (HA) is increasingly being evaluated and utilized to improve soil health and crop productivity in intensely farmed arid and semi-arid regions. However, the scientific comparison of field-scale use of single vs. repeated application of HA has not been reported. A field study was conducted to quantify the effect of different numbers of annual HA applications on (i) oat crop performance indicators, and (ii) the changes in soil health metrics in a dryland farming ecosystem. We found that multiple years of annual HA application improved crop growth, and increased grain protein yield (up to 60%), grain yield (21%), water use efficiency (22%), partial factor productivity of nitrogen (21%) and economic benefit (34%) over that for the control (no HA) during both a wetter and a drier growing season. The greater input of crop residue associated with higher yields led to an increase of soil organic carbon and water storage at both 0-20 and 20-60 cm soil layers, and a reduction in soil electrical conductivity, pH and bulk density with increasing years of HA application. There was an overall improvement in soil micro-environmental conditions. These in turn promoted an increased activity of the soil enzymes urease (up to 89%), invertase and catalase and soil nutrient turnover and availability (e.g. up to 58% higher plant available nitrogen). Our results show for the first time that repeated annual HA application of at least 2 years would be a cost-effective strategy to combat land degradation and nurture sustainable crop production in dryland agriculture under widely varying weather scenarios expected with climate change.