<b>Low-Cost Sensing for Integrated Soil and Water Assessment in Small-Scale Farming</b>

This study demonstrates that low-cost, consumer-grade technology, deployed within a participatory citizen science framework, can generate robust diagnostic insight to guide whole-system ecological redesign. Over a 48-hour period at Green Valley Farm (a pseudonym), we conducted a high-density reconnaissance using a smartphone-connected soil sensor (¥143) and a colorimetric water test kit (¥82.9), collecting 221 geotagged soil samples and analyzing eight distinct water sources.

The data revealed a landscape defined by disconnected flows and spatial dysfunction: (1) a severe nutrient blockage, with extreme fertility (index >3000) and salinity (EC up to 5,824 µS/cm) immobilized in animal manure and compost zones, while intensive vegetable gardens exhibited critically low fertility (index as low as 5); (2) a dysfunctional water cycle marked by both scarcity and saturation, with 68% of garden soils below optimal moisture (<15%) while compost and graywater zones were universally saturated (100% moisture); (3) a mismatched water cycle, where high-quality rainwater (pH 6.6, no heavy metals) was unharvested, alkaline and heavy-metal-positive pond water (pH 8.9) posed an irrigation risk, and ammonia-rich graywater (NH₃ >5.0 mg/L) was discarded as a pollutant; and (4) chaotic variability within management zones indicating absent systematic design.