Site-Specific Online Fertilizer Recommendations in Small Cardamom (Elettaria cardamomum (L.) Maton through CardSApp offers fertilizer savings and higher economic returns

The cultivation of small cardamom in the Indian Cardamom Hill (ICH) region of the Western Ghats, southern India, has become highly intensive, with heavy use of fertilizers and pesticides. The cultivation of small cardamom in the Indian Cardamom Hill (ICH) region of the Western Ghats, Southern India, has become highly intensive, with heavy use of fertilizers and pesticides. The ICH region is one of the world's biodiversity hotspots. Numerous studies have reported that the excessive use of chemical fertilizers has caused soil acidification (lowering of pH) and nutrient imbalances. This has resulted in unsustainable production of cardamom, a high-value spice crop that contributes significantly to India's export earnings. This study aimed to conduct a geo-tagged soil fertility survey in selected cardamom-growing areas within the ICH, assess soil fertility and provide sitespecific fertilizer recommendations to farmers via a mobile- or web-based application. A digital application, CardSApp, designed for the small cardamom sector, offers tailored fertilizer recommendations based on local soil and crop requirements. A representative geo-tagged soil survey was conducted in Udumbanchola taluk, located in Idukki district of Kerala, within the ICH. The surveyed area spanned from 76°59'01.19'' to 77°16'11.55'' East longitude and 9° 38'21.54'' to 10°04'46.60'' North latitude. Spatial interpolation techniques were used to generate maps showing the distribution of primary, secondary and micronutrients in the soil. The study revealed a high availability of NPK nutrients in cardamom soils. The study also revealed deficiencies in secondary nutrients like magnesium and sulfur, as well as micronutrients such as boron. Most of the soils showed signs of acidification. These findings highlight opportunities to optimize fertilizer usage and improve soil health. Specifically, NPK usage can be reduced or phosphatic fertilizers omitted in 58% of the area, potentially savings of ?12.27 crores annually in the surveyed taluk alone. Additionally, addressing deficiencies in secondary and micronutrients can further enhance soil health and crop productivity. To aid farmers in decision-making, the Android- and web-based application CardSApp leverages interpolated soil fertility data. CardSApp offers site-specific recommendations tailored to the soil nutrient profiles identified in the survey. CardSApp enables farmers to optimize fertilizer use, correct nutrient imbalances and apply amendments for pH correction. These practices can improve both farm productivity and income. The adoption of this online fertilizer recommendation system by farmers in the ICH is expected to rationalize fertilizer usage in cardamom cultivation, improve both soil and plant health and support sustainable production with higher economic returns.