🔧 Calibrating Sensors for Different Soil Types - One Size Does NOT Fit All

A sandy soil at 30% moisture is already dry and needs water. A clay soil at 30% moisture is still wet and does NOT need water. Using the same threshold for all soil types wastes water or causes drought stress. This lesson teaches you how to calibrate your system for YOUR specific soil.

📊 Soil Type Characteristics

🌾 How to Identify Your Soil Type

• Squeeze Test (Wet soil): Take a handful of moist soil and squeeze.
• 🏜️ Sandy: Falls apart immediately, feels gritty. Water drains fast - water frequently.
• 🪨 Sandy Loam: Forms a weak ball, breaks apart easily. Good drainage, moderate watering.
• 🌾 Loam: Forms a ball that holds together, breaks when poked. IDEAL - balanced watering.
• 🧴 Clay Loam: Forms a strong ball, feels smooth. Slow drainage - water less frequently.
• 🧱 Clay: Forms a tight, sticky ball that stays together. Very slow drainage - water rarely.

📖 Soil-Specific Threshold Code

/*
 * Soil-Specific Irrigation Thresholds
 * Adjust watering based on your soil type
 */

#include <Arduino.h>

#define SOIL_PIN 32

// ========== SOIL TYPE SELECTION ==========
// Uncomment YOUR soil type:
// String soilType = "Sandy";
// String soilType = "Sandy Loam";
String soilType = "Loam";          // Default - change to your soil
// String soilType = "Clay Loam";
// String soilType = "Clay";

// ========== SOIL CALIBRATION VALUES ==========
// Replace these with YOUR sensor's calibrated values
const int DRY_VALUE = 3800;   // Value in dry air
const int WET_VALUE = 1500;   // Value in water

// ========== GET SOIL-SPECIFIC THRESHOLDS ==========
int getWaterThreshold() {
    if (soilType == "Sandy") return 20;
    if (soilType == "Sandy Loam") return 25;
    if (soilType == "Loam") return 30;
    if (soilType == "Clay Loam") return 35;
    if (soilType == "Clay") return 40;
    return 30;  // Default
}

int getCriticalThreshold() {
    if (soilType == "Sandy") return 10;      // Wilting point ~10%
    if (soilType == "Sandy Loam") return 15;
    if (soilType == "Loam") return 20;
    if (soilType == "Clay Loam") return 30;
    if (soilType == "Clay") return 35;
    return 20;
}

int getFieldCapacity() {
    if (soilType == "Sandy") return 25;
    if (soilType == "Sandy Loam") return 35;
    if (soilType == "Loam") return 45;
    if (soilType == "Clay Loam") return 55;
    if (soilType == "Clay") return 65;
    return 45;
}

// ========== READ SOIL MOISTURE ==========
int readSoilMoisture() {
    int raw = analogRead(SOIL_PIN);
    int moisture = map(raw, DRY_VALUE, WET_VALUE, 0, 100);
    moisture = constrain(moisture, 0, 100);
    return moisture;
}

// ========== GET RECOMMENDATION ==========
String getRecommendation(int moisture) {
    int threshold = getWaterThreshold();
    int critical = getCriticalThreshold();
    int fc = getFieldCapacity();
    
    if (moisture <= critical) {
        return "🚨 CRITICAL: Soil extremely dry! Water IMMEDIATELY!";
    } else if (moisture < threshold) {
        return "💧 SOIL DRY: Start irrigation within 24 hours";
    } else if (moisture <= fc) {
        return "✅ OPTIMAL: Soil moisture adequate";
    } else if (moisture > fc) {
        return "⚠️ SOIL WET: Stop irrigation. Risk of over-watering";
    }
    return "Monitor conditions";
}

// ========== SETUP ==========
void setup() {
    Serial.begin(115200);
    pinMode(SOIL_PIN, INPUT);
    
    Serial.println("╔══════════════════════════════════════════════════════════════╗");
    Serial.println("║              🔧 SOIL-SPECIFIC IRRIGATION SYSTEM              ║");
    Serial.println("╚══════════════════════════════════════════════════════════════╝");
    
    Serial.printf("\n🌾 Soil Type: %s\n", soilType.c_str());
    Serial.printf("💧 Water threshold: %d%%\n", getWaterThreshold());
    Serial.printf("🚨 Critical threshold: %d%%\n", getCriticalThreshold());
    Serial.printf("💧 Field Capacity: %d%%\n", getFieldCapacity());
    Serial.println("");
}

// ========== LOOP ==========
void loop() {
    int moisture = readSoilMoisture();
    int threshold = getWaterThreshold();
    int critical = getCriticalThreshold();
    
    Serial.println("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━");
    Serial.printf("📊 Soil Moisture: %d%%\n", moisture);
    Serial.printf("🎯 %s threshold: %d%%\n", soilType.c_str(), threshold);
    Serial.printf("💚 %s\n", getRecommendation(moisture).c_str());
    
    // Decision logic
    if (moisture < threshold) {
        if (moisture < critical) {
            Serial.println("🔴 ACTION: EMERGENCY irrigation required NOW!");
        } else {
            Serial.println("🟡 ACTION: Schedule irrigation for today");
        }
        // startIrrigation();
    } else if (moisture > getFieldCapacity()) {
        Serial.println("🟢 ACTION: Stop irrigation - soil too wet");
    } else {
        Serial.println("✅ ACTION: No irrigation needed - monitor");
    }
    
    Serial.println("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\n");
    
    delay(60000);  // Check every minute
}
    

🎯 Key Takeaways:

• ✅ Sandy soils need lower thresholds (15-20%) - water frequently, small amounts
• ✅ Clay soils need higher thresholds (35-40%) - water rarely, deep watering
• ✅ Loam is ideal (25-30% threshold) - best for most crops
• ✅ Field Capacity = STOP watering; Wilting Point = CRITICAL
• ✅ Always configure your soil type in code - one threshold does NOT fit all
• ✅ Adjust thresholds based on crop growth stage (seedlings need more water)