Effect of fertilizer level and seaweed sap on productivity and profitability of rice (Oryza sativa)

A field experiment was conducted during the rainy (kharif) season of 2012 and 2013 at Birsa Agricultural University, Ranchi, Jharkhand, to study the effect of fertilizer level, seaweed sap and its concentration on the productivity and profitability of rice (Oryza sativa L.). Treatments consisted of 2-fertilizer levels, viz. 100 and 50% recommended fertilizer in main plot, 2 sap source, viz. Kappaphycus alvarezii and Gracilaria edulis in subplot and 6 sap concentration spray, viz. 0 (water), 2.5, 5.0, 7.5, 10.0 and 15% in sub-subplot, laid out in a split-split-plot design and replicated thrice. Rice fertilized with 100% recommended fertilizer (120 kg N + 26.2 kg P + 33.2 kg K/ha) produced higher productive tillers (252.2/m²), grains/panicle (65.2), panicle length (21.2 cm) resulting in higher grain (3.1 t/ha) and straw (4.2 t/ha) yield, net returns (22.5 × 10³/ha), benefit: cost ratio (0.89) and nitrogen, phosphorus, potassium and sulphur uptake in grain and straw than 50% recommended fertilizer. Crop sprayed with Kappaphycus alvarezii had produced more grains/panicle (65.9) and longer panicles (20.7 cm), resulting in higher grain yield (3.0 t/ha), net returns (22.8 × 10³/ha), benefit: cost ratio (0.96) and NPKS uptake by grain and straw than Gracilaria edulis. Spraying of 10% sap concentration resulted in significantly more productive tillers (269.2/m²), panicle length (21.9 cm), 1, 000-grain weight (24.0 g) resulting in higher grain yield (3.5 t/ha), net returns (28.6 × 10³/ha), benefit: cost ratio (1.17) and nutrient uptake of NPKS by grain and straw as compared to lower concentration. The interaction effect between fertilizer and seaweed sap also showed that rice receiving 100% recommended fertilizer and sprayed with 10% Kappaphycus alvarezii was more productive and remunerative as it gave more productive tillers (288.4), grain yield (4.2 t/ha), straw yield (5.4 t/ha), net returns (37.1 × 10³/ha) and benefit: cost ratio (1.42) than the remaining combinations of fertilizer level, sap and its concentration. Further, crop fertilized with 50% recommended fertilizer and sprayed 2.5% concentration of either Kappaphycus alvarezii or Gracilaria edulis was as productive and remunerative as that of 100% recommended fertilizer alone. Hence application of 2.5% either Kappaphycus alvarezii or Gracilaria edulis sap can curtail the 50% fertilizer requirement of the crop.