Customized fertilizer formulations for elephant foot yam (Amorphophallus paeoniifolius (Dennst.) Nicolson) under intercropping in coconut gardens for Kerala, India

Among tropical tuber crops, elephant foot yam ( Amorphophallus paeoniifolius (Dennst.) Nicolson) is a highly potential and ideal intercrop in the coconut gardens of Kerala, especially in agro-ecological unit (AEU) 3 and AEU 9 with laterite and sandy soil types, respectively. This paper narrates the protocols developed for evolving customized fertilizer (CF) formulations for elephant foot yam (EFY) under intercropping in coconut gardens of Kerala including their testing and validation in different parts of the State to arrive at the best grade and rate of application. The methodology included, arriving at the weighted average data of each chemical parameter of the two AEUs and the theoretical optimum of the nutrient recommendation evolved for N, P, K, Mg, Zn, B, dolomite based on the weighted average data was 71: 12.5: 106.5: 12.8: 4.2: 1.31: 1000 kg ha-1 for AEU 3 and 78: 12.5: 90: 12.8: 4.2: 1.31: 1000 kg ha-1 for AEU 9, respectively. The actual optimum nutrient doses evolved based on nutrient omission plot (NOP) and nutrient level (NL) experiments for N, P, K, Mg, Zn, B and dolomite was 140: 20: 225: 19.2: 4.2: 1.575: 1500 kg ha-1 for AEU 3 and 160: 12.5: 180: 19.2: 6.3: 1.975: 1500 kg ha-1 for AEU 9, respectively. Based on the nutrient use parameters computed for an yield target of 45 t ha-1, as per soil test crop response (STCR), quantity of nutrients to be supplied through CF formulation was arrived as 203 and 185, 58 and 63, 145 and 175 kg N, P2O5 and K2O, respectively for AEU 3 and AEU 9. In the case of secondary and micronutrients, the level at which the highest tuber yield obtained as 19.2, 4.2 and 1.575 kg ha-1 Mg, Zn, B, respectively for AEU 3 and 19.2, 6.3 and 1.975 kg ha-1 for AEU 9 was taken. Considering the nutrient content in the CF as 20% N and 70% K, for an application rate of 500 kg ha-1, the grades of the CF based on STCR approach was arrived as N: P2O5: K2O: Mg: Zn: B is 8: 11: 21: 3.5: 1: 0.3 for AEU 3 (CF1) and 7: 12: 24: 3.5: 1.25: 0.4 for AEU 9 (CF2). In the response curve (RC), the nutrient levels at the highest tuber yield obtained under NOP and NL was taken and the grades of N: P2O5: K2O: Mg: Zn: B arrived was 7: 3: 25: 4: 1.25: 0.4 for AEU 9 (CF3) and 6: 3: 30: 3.5: 1: 0.3 for AEU 3 (CF4). Among these four grades, the first three grades tested at two doses viz. 500 and 625 kg ha-1 in three farmers’ fields of the two AEUs indicated better performance of all the three grades @ 625 kg ha-1. The three grades @ 625 kg ha-1 tried in large plots of the five major EFY growing districts of Kerala viz. Thiruvananthapuram, Kollam, Pathanamthitta, Kottayam and Ernakulam for profitability, soil health and tuber quality revealed CF2 with grade as N: P2O5: K2O: Mg: Zn: B @ 7: 12: 24: 3.5: 1.25: 0.4 as the best in terms of tuber yield, BC ratio, soil quality indices and biochemical attributes of the tuber.