Priyabrata Santra

Spatial prediction of soil properties in a watershed scale through maximum likelihood approach

Surface map of soil properties plays an important role in various applications in a watershed. Ordinary kriging (OK) and regression kriging (RK) are conventionally used to prepare these surface maps but generally need large number of regularly girded soil samples. In this context, REML-EBLUP (REsidual Maximum Likelihood estimation of semivariogram parameters followed by Empirical Best Linear Unbiased Prediction) shown capable but not fully tested in a watershed scale. In this study, REML-EBLUP approach was applied to prepare surface maps of several soil properties in a hilly watershed of Eastern India and the performance was compared with conventionally used spatial interpolation methods: OK and RK. Evaluation of these three spatial interpolation methods through root-mean-squared residuals (RMSR) and mean squared deviation ratio (MSDR) showed better performance of REML-EBLUP over the other methods. Reduction in sample size through random selection of sampling points from full dataset also resulted in better performance of REML-EBLUP over OK and RK approach. The detailed investigation on effect of sample number on performance of spatial interpolation methods concluded that a minimum sampling density of 4/km2 may successfully be adopted for spatial prediction of soil properties in a watershed scale using the REML-EBLUP approach.

Selection of soil physical quality indicators in relation to soil erodibility

Soil quality indices based on soil characteristics can be used to assess the sustainability of soil and to assist in soil management decisions. Principal component analysis (PCA) technique was used to identify dominant soil characteristics in relation to soil erodibility in watersheds of submontane Punjab (India). Soil physical and chemical characteristics were evaluated for four locations with four land uses at each location whereas runoff, soil loss and soil erodibility were determined at two locations under natural rainfall conditions and at four locations under simulated rainfall conditions. PCA was performed on 22 physical and chemical soil characteristics, which grouped these soil characteristics into five distinct principal components (PCs). These five PCs namely soil hydraulic factor, density factor, structural factor, sand factor and cation factor, explained 86% variability in data. These PCs also explained 86, 96 and 93% variability under natural rainfall conditions and 75, 76 and 77% variability under simulated rainfall conditions in relation to runoff, soil loss and soil erodibility, respectively. Soil total organic carbon content can be considered as dynamic soil physical quality indicator and can be used to monitor temporal and spatial changes in soil quality.

Pedotransfer functions to estimate soil water content at field capacity and permanent wilting point in hot Arid Western India

Characterization of soil water retention, e.g., water content at field capacity (FC) and permanent wilting point (PWP) over a landscape plays a key role in efficient utilization of available scarce water resources in dry land agriculture; however, direct measurement thereof for multiple locations in the field is not always feasible. Therefore, pedotransfer functions (PTFs) were developed to estimate soil water retention at FC and PWP for dryland soils of India. A soil database available for Arid Western India (N=370) was used to develop PTFs. The developed PTFs were tested in two independent datasets from arid regions of India (N=36) and an arid region of USA (N=1789). While testing these PTFs using independent data from India, root mean square error (RMSE) was found to be 2.65 and 1.08 for FC and PWP, respectively, whereas for most of the tested ‘established’ PTFs, the RMSE was >3.41 and >1.15, respectively. Performance of the developed PTFs from the independent dataset from USA was comparable with estimates derived from ‘established’ PTFs. For wide applicability of the developed PTFs, a user-friendly soil moisture calculator was developed. The PTFs developed in this study may be quite useful to farmers for scheduling irrigation water as per soil type.

Digital Soil Mapping and Best Management of Soil Resources: A Brief Discussion with Few Case Studies

Soil plays a key role in agricultural production system by supporting plant growth as well as in hydrological cycle by partitioning rainwater into runoff and infiltration. Therefore, knowledge on soil properties helps in better management of both soil and water resources for sustainable crop production. However, soils vary largely in space and therefore characterizing it for a particular landscape with a set of soil parameters is a difficult task. Often, there is need to collect multiple soil samples from a landscape for characterization purpose in order to minimize the spatial variation effect and is not always feasible. Most of the times, a homogeneous zone is assumed with similar soil properties to eliminate the variation effect. Soil mapping helps in characterizing the soil resources in a better way and recently introduced digital soil mapping approach is more appropriate for this purpose. In this approach, spatial variation of soil properties and its relation with other landscape and environment variables in the form of ‘scorpan’ factors are considered while mapping soil properties in a spatial domain. Mathematical models are also established between soil properties and environment variables exploiting the available legacy soil data and hugely available digital data on earth features in recent times. Hyperspectral soil signatures have also a potential role to improve the digital soil products further. In this chapter, we discuss the basics of digital soil mapping approach and its needs, semivariogram fitting, kriging and its variations, accuracy and uncertainty of digital maps, role of pedotransfer (PTF) and spectrotransfer (STF) models in digital soil mapping, future prospect of hyperspectral signatures in mapping soil properties and few cases studies on digital soil mapping. Finally, it is expected that digital soil maps are available in different IT platforms, e.g. internet, desktop computer, mobile apps, webGIS platform, etc., to make them useful to end users.

Development of Phase Change Material-Based Temperature Regulation Facility Inside Protected Agriculture Structure

In arid agriculture, protected cultivation inside structures with polythene or shade net as covered material may be found beneficial to avoid aberrant weather conditions. However, significant amount of heat load is generated inside the structure due to high solar irradiation and trapping of outgoing longwave radiation due to protected covers, which lead to uncongenial conditions for sustainable plant growth. With a view to regulating temperature inside the protected cultivation structure, phase change material (PCM)-based temperature regulation facility was tried to develop through laboratory trials and experiments. Mixtures of paraffin liquid and paraffin wax in different ratios were prepared in the laboratory and heat change of the mixture material was recorded during heating and cooling process in a controlled water bath experimental setup. A mixture of paraffin liquid and wax in the ratio 10:1 was found suitable as a phase change material with melting temperature at about 35–38 °C. In the second stage, two heat exchanger structures consisting of GI sheet tank of 6.5 L capacity and aluminium fins attached at both sides of the tank for better heat transfer with air were designed and fabricated and these were tested inside small experimental structures with fibre glass sheet casing and covers. A decrease of inside temperature by 8–10 °C has been observed inside prototype structure with the incorporation of PCM material compared to one without it. Subsequently, the system was kept inside the PV clad enclosure (13.5 m2) and the performance of the enclosure was studied with chilli crop grown inside. The amount of heat stored by a single PCM storage system with 2.5 kg PCM materials was found about 1100–1200 kJ. An estimate indicates that it is sufficient to reduce the inside temperature by 1 °C for four hours if number of air change rate is 30 per hour. However, long-term trials are required to ascertain number of cycles of heating and cooling of the material.

Design, Development and Performance Evolution of a Low-Cost Solar Dryer

Considerable amount of fruits and vegetables have been wasted due to non-availability of appropriate processing facilities in farmers field, in spite of high production in India with second rank in the world. A little of total fruit and vegetable productions in the country have been processed in industries. It has been noted that food crisis in most parts of the world is due to non-availability of processing and preserving facility rather than due to low production. Spoilage of fruits and vegetables can be reduced by drying and preserving them by suitable solar devices. Keeping in mind this requirement, a simple solar dryer has been fabricated at ICAR-CAZRI, Jodhpur. The dryer comprises a drying tray (0.75 m × 0.53 m) made of wooden frame and SS wire mesh and a glass sheet (4 mm thick) fitted on a wooden frame and a couple of hinges with opening and closing arrangements. Suitable openings for entry of ambient air and exit of water vapour have also been provided. The cost of the dryer is about Rs. 800. The drying tray serves dual purpose of solar collector and drying chamber. The maximum stagnation temperature observed inside the drying chamber was 63 °C on loading of 3 kg ber (Ziziphus sp.). It was 49 °C, when the outside ambient temperature was 27 °C on a clear sunny day (from 10 am to 4 pm) in the month of December–January. For drying of 3 kg ber fruits to a final weight of 1 kg using the developed dryer, it took about 7–8 days. It has been observed that the drying time for Ziziphus (ber) decreased by 50% in comparison to open sun drying. The developed dryer was also successfully tested to dry spinach (Spinacia oleracea), grated aonla (Phyllanthus emblica) and beetroot (Beta vulgaris). This solar dryer would be very useful for small and marginal farmers.