| Abstract |
A study entitled “Soil quality assessment and rejuvenation of coastal sandy <br/>soils of Thiruvananthapuram district (AEU 1) through organics” was carried out <br/>with an objective in assessment of soil quality of coastal sandy soils in<br/>Thiruvananthapuram district (AEU 1) and development of organics based <br/>rejuvenation methods. The study was carried out in two phases. As phase 1, <br/>characterization of southern coastal soils of AEU 1 in Thiruvananthapuram district <br/>was done. Based on the results of phase I, an area with low fertility was selected for <br/>phase 2 of the study. Different organic amendments were applied to study the effect <br/>on soil properties and crop growth in phase 2.<br/>Fifty geo-referenced surface soil samples, along with core samples were <br/>collected from coastal areas in AEU 1 of Thiruvananthapuram district and <br/>characterized for various physical (texture, bulk density, particle density, water <br/>holding capacity and soil aggregate stability), chemical (pH, EC, cation exchange <br/>capacity, exchangeable acidity, organic carbon, available macronutrients, available <br/>micronutrients such as Fe, Mn, Zn, Cu, B, Cl, Na and heavy metals (Pb and Cd))<br/>and biological attributes (dehydrogenase activity and microbial biomass carbon).<br/>Principal component analysis was used to set up the minimum data set of <br/>indicators to compute the soil quality index. Six principal components were <br/>extracted from which ten indicators that highly influenced the soil quality were <br/>identified, viz. clay per cent, water holding capacity, bulk density, soil pH, organic <br/>carbon, available K, available S, available Zn, available Mn and available B. Scores <br/>and weights were assigned to each indicator, and were aggregated to compute the <br/>soil quality index. The relative soil quality index of the soils were also found. GIS <br/>techniques were used to prepare thematic maps of major soil attributes and relative <br/>soil quality indices of the coastal sandy soils of AEU 1. Correlations were worked <br/>out among the various analysed parameters.<br/>The analytical results for soil physical properties showed that the predominant <br/>soil textual class observed in the present study area was sand and loamy sand. Bulk <br/>192<br/>density was in the range of 1.37 - 1.86 Mg m-<br/>³, particle density 2.22 - 2.89 Mg m-<br/>³, <br/>with 22.7 – 56 per cent water holding capacity and 33.6-59.4 per cent soil aggregate <br/>stability. The soil pH ranged between 5.11 - 7.19, and 0.03 - 0.23 dS m-1<br/>for electrical <br/>conductivity. Organic carbon was found in the range of 0.07 - 1.01 per cent, nitrogen <br/>100 - 308 kg ha-1<br/>, phosphorus 7.05 - 59.94 kg ha-1<br/>and potassium 100 - 361 kg ha-1<br/>. <br/>Secondary nutrients ranged as: calcium 80 - 360 mg kg-1<br/>, magnesium 47 - 152 mg <br/>kg-1<br/>and sulphur 4.5 - 20.5 mg kg-1<br/>. The available micro nutrients ranged between: <br/>6.63 - 81.57 mg kg-1<br/>for iron, 2.53 - 36.01 mg kg-1<br/>for manganese, 2.21 - 16.64 mg <br/>kg-1<br/>for zinc, 0.11 - 6.07 mg kg-1<br/>for copper and 0.11- 0.82 mg kg-1<br/>for boron. Heavy <br/>metals such as Cd and Pb were below detectable limit. Soil biological activity in <br/>these soils were poor with dehydrogenase activity in the range of 5.57 – 20.29 µg <br/>TPF hydrolysed g-1<br/>soil 24 hrs-1<br/>and microbial biomass carbon of 9.18 - 29.96 µg g1<br/>soil. So, generally the fertility status of this coastal sandy soils was found to be <br/>low.<br/>Majority of the soils belonged to medium soil quality (60 %), followed by <br/>good (36 %) and poor (4 %) quality. The soils of Kadakkavoor recorded the highest <br/>soil quality index and that of Anchuthengu, recorded the lowest. <br/>Based on the results of phase I, a pot culture experiment was done at <br/>Kochuveli, Industrial area, Thiruvananthapuram with Amaranthus (variety: Arun)<br/>as test crop. The experiment was completely randomized design (CRD) with 12 <br/>treatments and 3 replications. <br/>In the pot culture experiment, treatments included were; T1: Control, T2: <br/>Organic POP, T3 : Vermicompost, T4: Liming + Vermicompost, T5 : Coir pith <br/>compost, T6: Liming + Coir pith compost, T7: City compost, T8: Liming + City <br/>compost, T9: Suchitha, T10: Liming + Suchitha, T11: FYM 12.5 t ha-1 + Biochar 12.5 <br/>t ha-1<br/>, T12: Liming + FYM 12.5 t ha-1 + Biochar 12.5 t ha-1<br/>. In T2 (organic POP),<br/>FYM @ 25t ha-1<br/>as basal dose and top dressing with fresh cow dung slurry @ 1kg <br/>per 10 litres (50 kg ha-1<br/>) was done. Along with that, 272.7 kg rock phosphate and <br/>122.5 kg potassium sulphate ha-1 were applied. From T3 to T10, as per organic POP <br/>manure recommendation, basal dose of FYM was substituted with organic <br/>amendments @ 25 t ha-1 with or without lime application.<br/>193<br/>Soil management using organic manures had considerable impact on growth <br/>and yield characteristics of plant. Highest plant height was observed in T8, which <br/>was on par with T4 and T10. Highest dry matter and yield were recorded in T10 which <br/>was followed by T4. Effect of organic manures on quality parameters showed that <br/>highest β carotene and nitrate content were recorded in T10. Highest vitamin C <br/>content was recorded in T10 which was on par with T3 and T4. Being an antinutritional factor, T1 recorded the highest value of oxalate content and the lowest <br/>was seen in T10. Regarding the nutrient uptake in plants, T10 recorded the highest <br/>uptake of N, K, Ca and Mg, while T4 recorded the highest in P and S uptake.<br/>Analyses of post-harvest soil for nutrient parameters showed that the highest <br/>value of organic carbon was recorded in T10, which was on par with T8 and T9. The <br/>highest value for available nitrogen was recorded for T10 while the highest value for <br/>available phosphorous was recorded in T4. The potassium content was found to be <br/>the highest in T10. Also T10 showed the highest value in available secondary <br/>nutrients. Micronutrients analyses showed that highest content of available Fe was <br/>present in T3, while highest of available Cu, Zn and B were recorded in T10. T9<br/>showed the highest value in available Mn. T1 showed highest available Na and Cl <br/>content.<br/>Analyses of soil biological properties due to the effect of organic manure <br/>addition showed that the highest value of dehydrogenase activity was found in T8, <br/>which was statistically on par with T7 and T10. Also, the highest value in microbial <br/>biomass carbon was found in T8, which was on par with T7, T9, and T10. The <br/>highest B: C ratio was recorded by T10.<br/>From the study, it is concluded that soil test based lime application and basal <br/>application of Suchitha @ 25 t ha-1<br/>, top dressing with fresh cow dung slurry @ 1kg <br/>per 10 litres, along with 272.7 kg rock phosphate and 122.5 kg potassium sulphate <br/>ha-1 was observed to be the best treatment to improve the soil quality, yield and <br/>quality parameters of amaranthus in coastal sandy soils of AEU 1 in <br/>Thiruvananthapuram district. |
