PhD

The investigation entitled “Input optimization for medicinal rice (Oryza sativa L.) cv. Njavara” was conducted at Instructional Farm, College of Agriculture, Vellayani, Thiruvananthapuram, Kerala, during the summer seasons of 2007 and 2008 (January to April) to standardize an ideal nutrient schedule under two moisture regimes for sustaining Njavara production in lowlands, to investigate the soil physical, chemical and biological properties as influenced by regimes and sources of nutrients and to work out the economics of Njavara cultivation. Both the experiments (submerged and saturated situations) were laid out in randomised block design with ten treatments each and three replications. The treatments comprised four nutrient regimes viz., N1 - 30:15:15, N2 - 30:30:30, N3 - 40:20:20 and N4 - 40:40:40 kg NPK ha-1, two nutrient sources viz., organic nutrient source (S1) and integrated nutrient source (S2) and two controls viz., absolute control (no nutrient was applied) (C1) and POP for local rice variety (C2).
Growth components like plant height, leaf number plant-1, leaf area index (LAI), number of tillers m-2, culm strength and flag leaf area, yield and yield attributes like number of productive tillers m-2, panicle length, number of grains panicle-1, number of filled grains panicle-1, 1000 grain weight, harvest index, sterility percentage, dry matter partitioning, paddy grain ratio and grain husk ratio were recorded. Leaf chlorophyll content was also estimated. Uptake of nutrients (N, P, K, S, Fe, Mn and Zn) and economics of cultivation were computed. Biochemical components of grains such as total, free and sulphur containing amino acids, phenols, starch, amylose, amylopectin and protein content were estimated. Data on weed biomass, weed flora and crop duration were also recorded. Soil enzymes (urease, phosphatase and dehydrogenase), soil microbial population (bacteria, fungi and actinomycetes population) and soil fertility status (available nitrogen, phosphorus, potassium, sulphur, iron, zinc and manganese) were assessed before and after the crop.
Effect of nutrient regimes
Effect of nutrient regimes on all growth parameters was significant. Growth parameters like plant height, leaf number plant-1, leaf area index (LAI), number of tillers m-2, culm strength and flag leaf area were significantly higher in N2. N2 recorded leaf chlorophyll content which was significantly higher than N3 and N1 and was on par with N4.
All yield attributes except 1000 grain weight were significantly influenced by nutrient regimes resulting in significant variation in the crop yield (grain and straw). Maximum grain yield was recorded in N2 (30:30:30 kg NPK ha-1) (2.78 and 2.66 t ha-1) which was on par with N4 (40:40:40 kg NPK ha-1) (2.67 and
2.58 t ha-1) and was significantly superior to N1 and N3 under submerged and saturated situations respectively. Duration of the crop did not show significant variation due to nutrient regimes.
Total amino acid and protein content of grain were significantly influenced by nutrient regimes and were maximum in N2.
Nutrient regimes significantly influenced N, P and K uptake. Uptake of N, P and K in N2 was significantly higher than that in the other three nutrient regimes. Nutrient regimes did not significantly influence uptake of S, Fe, Mn and Zn.
Results of the study also revealed that Echinochloa colona (L.) Link, Isachne miliacea Roth ex Roem. et Schult; Cyperus iria L., Cyperus difformis L. Fimbristylis miliacea (L.) Vahl.; Marsilea quadrifoliata Linn., Monochoria vaginalis (Burm. f.) Presl. ex Kunth and Ludwigia perennis L were the most predominant weed species in the experimental field under both situations. Weed biomass at 20 and 40 DAS were not significantly influenced by nutrient regimes during both the years of experimentation.
Nutrient regimes showed significant influence on available nitrogen, phosphorus and potassium status of the soil after the investigation. Available sulphur, iron, zinc and manganese status of the soil after the experiment revealed non-significant effect of nutrient regimes in both the years of study.
Among the soil enzymes, urease activity was influenced significantly by the nutrient regimes and it was in the order N4 > N3 > N2 > N1. Bacterial population was influenced significantly by the nutrient regimes and it was in the order N4 > N3 > N2 > N1.
Effect of nutrient sources
Nutrient sources had significant influence on all the growth characters, yield attributing characters like number of grains panicle-1, number of filled grains panicle-1, harvest index as well as crop yield (grain and straw). Highest number of grains panicle-1, filled grains panicle-1 and crop yield (grain and straw) were realized in integrated nutrient source and they were significantly higher than that realized from organic source. Duration of crop did not differ significantly between the nutrient sources.
Integrated nutrient source registered significantly higher nitrate reductase activity and root weight compared to organic source. Biochemical components such as total, free and sulphur containing amino acids, phenols, starch, amylose, amylopectin and protein content of grain did not differ significantly between nutrient sources.
Highest uptake of N, P and K was in integrated nutrient source. Sources of nutrients did not influence uptake of S, Fe, Mn and Zn during both the years of experimentation.
Weed biomass under different nutrient sources at both 20 DAS and 40 DAS differed significantly from one another. Weed biomass during both stages and both the years of experimentation was more in organic source compared to integrated nutrient source. Highest weed biomass was recorded in absolute control at both stages during both the years.
Available nitrogen, available phosphorus and available potassium status of the soil after the experiment in the plots receiving integrated nutrient source and organic nutrient source differed significantly from each other. Available N, P and K status of the soil were higher in integrated nutrient source. Organic carbon, available sulphur, iron, zinc and manganese status of the soil after the experiment were not significantly influenced by nutrient sources.
Urease activity and bacterial population in the soil were influenced significantly by nutrient sources. Highest activity of urease and bacterial population in the soil were recorded in organic source compared to integrated nutrient source. Phosphatase and dehydrogenase activity as well as fungal and actinomycetes population in the soil were not influenced by nutrient sources.
Economics of crop production
Gross income, net income and BCR were highest in N2S2. Application of FYM @ 5 t ha-1 along with 30:30:30 kg NPK ha-1 (50 % N as organic + 50 % N as chemical fertilizer) (N2S2) recorded a net profit of Rs 57,586 ha-1 and Rs 53,546 ha-1 under submerged and saturated situations respectively. The lowest gross income, net income and BCR were recorded in N1S1 (FYM @ 5 t ha-1 along with 30:15:15 kg NPK ha-1 as organic source).
The ideal nutrient schedule for sustaining Njavara production in lowlands under both submerged and saturated situations is N2S2 - FYM @ 5 t ha-1 + 30:30:30 kg NPK ha-1 (50 % N as organic + 50 % N as chemical fertilizer). This nutrient system realised highest grain yield, straw yield and net income.