PhD

The study entitled “Customized nutrient management for rice (Oryza sativa L.) in the Southern Laterites (AEU 8)” was undertaken at College of Agriculture, Vellayani during 2016 to 2019. The main objectives were to assess and rate the available nutrient status of rice soil in the Southern Laterites (AEU 8), to develop a Zn – B mix for rice and to evaluate the effect of the mix on rice, at different N/K ratios.
The study was carried out in three parts. The first part was on assessment and rating of available nutrient status of rice soil in Southern Laterites (AEU 8). Southern Laterites is spread over five blocks (Athiyannoor, Parassala, Nemom, Perumkadavila and Vellanad). Parassala, Nemom and Perumkadavila were selected for the study since paddy cultivation was observed in comparatively larger area in these blocks. One hundred and fifty, geo-referenced soil samples were collected from the rice fields during April to May 2017, at random from the 11 panchayats spread over these three blocks. The soil samples were analysed and rated for 14 soil fertility parameters and block wise digital maps were prepared with ArcGIS 10.1.
Based on the nutrient index, it was observed that organic carbon, available Ca, Mg, S, Cu, Zn and B recorded low nutrient indices (< 1.5) in all the three blocks. While available N was low in Nemom and Perumkadavila, it was medium (1.5 – 2.5) in Parassala block. Available P showed high index (> 2.5) in Parassala and Perumkadavila and medium index in Nemom. While Parassala and Nemom blocks could be rated as medium with respect to available K, Perumkadavila exhibited high index for K. Available Fe and Mn were high in all the blocks. The rice soils of Southern Laterites were observed to be strongly acidic with a mean pH of 5.27 ± 0.58, normal in electrical conductivity (0.77 ± 0.31) dS m-1, low in organic carbon (0.52 ± 0.23) % and available N (263.70 ± 49.32) kg ha-1, high in available P (90.40 ± 59.78) kg ha-1 and medium in available K (228.94 ± 87.84) kg ha-1. The soils were low in available Ca (15.78 ± 4.96) mg kg-1, available Mg (5.87 ± 1.85) mg kg-1 and available S (1.34 ±
0.83) mg kg-1. Among the micronutrients tested, the rice soils exhibited deficiency of available Cu (0.44 ± 0.22) mg kg-1, Zn (0.77 ± 0.19) mg kg-1 and B (0.315 ± 0.002) mg kg-1.
The second part of the study comprised development of a Zn – B mix for rice. The Zn and B requirement was calculated based on the difference between the crop requirement and Zn and B status of the soil. Crop requirement of Zn and B was computed as the product of the potential yield and whole plant nutrient composition. Accordingly, the Zn and B requirement could be calculated as 4.088 kg ha-1 and 0.738 kg ha-1 respectively. The Zn – B mix for rice was formulated by mixing zinc sulphate heptahydrate (ZnSO4.7H2O) and boric acid (H3BO3) in the ratio 4 : 1.
The third part of the study was a field experiment to assess the effect of the Zn – B mix on rice, at different N/K ratios. The experiment was conducted during the second crop season (September to January) of 2017 and 2018. The experiment was located in the Chenkal panchayat of Parassala block, in a farmer’s field where Zn and B deficiency was identified from the first part of the study. The experiment was laid out in randomised block design with 13 treatments (12 + 1), replicated thrice. The treatments T1 to T4 were combinations of N/K (1.0 : 0.5) + foliar application of 0.5 % and 1.0 % Zn – B mix at maximum tillering (MT) and panicle initiation (PI) stages, T5 to T8 were N/K (1.0 : 1.0) + foliar application of 0.5 % and 1.0 % Zn – B mix at MT and PI stages, T9 to T12 were N/K (1.0 : 1.5) + foliar application of 0.5 % and 1.0 % Zn – B mix at MT and PI stages and T13 was control (KAU POP for rice). The variety used for the study was Uma (MO 16). The soil of the experimental site was sandy clay loam, strongly acidic in reaction, low in organic carbon, medium in available N and K, high in available P and deficient in available Ca, Mg, Zn and B. In all treatments except control, nutrients were applied on soil test basis.
The results revealed that growth attributes were significantly influenced by N/K ratio and foliar application of Zn- B mix and the treatments were observed to be
superior to control (KAU POP). Mean tiller count and leaf area index were significantly higher with N/K (1.0 : 1.5) + foliar application of 0.5 % Zn – B mix at PI stage (T10) at MT and PI stages. It was on a par with T9, T11 and T12. However, the mean total dry matter production (12356 kg ha-1) was significantly higher with T12 (N/K (1.0 : 1.5) + foliar application of 1.0 % Zn – B mix at PI stage) and was comparable with T10.
Among the yield attributing characters, mean number of productive tillers m-2 (488.35) and grain weight per panicle (2.78 g) were significantly higher with T12 and were at par with T10. The treatments T10 and T12 were comparable with respect to the number of spikelets per panicle, filled grains per panicle and sterility percentage. The treatment T12 resulted in significantly higher mean grain yield (5.67 t ha-1) and was comparable with T10 (5.61 t ha-1). Straw yield was higher with T12 (6.89 t ha-1) and was on a par with T10 (6.83t ha-1). The treatments were superior to control (KAU POP), with T10 recording 43.9 per cent improvement in grain yield. Crude protein content of grain and uptake of major nutrients, Ca, Zn and B were significantly higher with T12 and was comparable with T10. Incidence of rice bug (at the milk stage) and false smut disease (at harvest) was observed during both the years. Mean benefit cost ratio was higher (1.72) with T10 and was comparable with T12 (1.69) as against a BCR of 1.16 for the KAU POP.
The present study revealed that the fertility status of rice soils of the Southern Laterites (AEU 8) need to be addressed in terms of soil acidity, low organic carbon status, build-up of phosphorus and deficiency of secondary nutrients and micronutrients like Zn, B and Cu, on soil test basis. Based on the crop requirement and nutrient status of the soil, a Zn – B mix was formulated, as a mixture of zinc sulphate heptahydrate and boric acid in the ratio 4 : 1. Application of nitrogen and potassium in the ratio 1.0 : 1.5 along with foliar application of 0.5% Zn – B mix at panicle initiation stage was observed to be effective in enhancing the growth and yield attributes, yield and economics of rice in the Southern Laterites (AEU 8) of Kerala