A Soil Health Card (SHC) for soil quality monitoring of agricultural lands in south-eastern coastal region of Bangladesh

Study area

Noakhali district is located at the south-eastern coastal region of Bangladesh. Geographically it lies between 22˚06′ and 23˚17′ North latitudes and between 90˚38′ and 91˚35′ East longitude (Fig. 1). The total area of Noakhali is 3685.87 Sq. km and the population is 310808.3 million (BBS 2011). The annual average temperature of this district ranges from a maximum of 34.3 °C to a minimum of 14.4 °C and average annual rainfall is 3302 mm. The area represents an extensive flat, coastal and deltaic land, located on the tidal floodplain of the Meghna River delta, characterized by flat land and low relief. The area is influenced by diurnal tidal cycles and the tidal fluctuations vary depending on seasons, being pronounced during the monsoon season. The economy of Noakhali is depends on agriculture and they produce varieties of crops, namely local and hybrid rice, wheat, vegetables, spices, cash crops, pulses, betel leaves, peanuts, onion, oil seeds and others. 30% of the regional GDP comes from agriculture with 45% of the population employed in the sector (BBS 2011). Noakhali, being exposed to the Bay of Bengal is prone to multiple hazards. Cyclones are frequently occurring disasters, which hit the coastal villages every year. Sometimes, cyclones accompanied by tidal surge inundate the very remote coastal areas of the district and cause massive destruction. Along with these, annual flooding due to excessive rainfall and poor drainage systems has recently been devastating (Banglapedia 2016).

Sampling and laboratory analysis

Soil samples were collected during January 2016 from ten fields of the study area (Fig. 1) before land preparation from plough-depth maintaining the ideal soil sampling protocol (Gupta 2000). Five samples were collected from each fields and analyzed for pH, EC, OC, OM, TN, P, K, S and B in regional laboratory of Soil Resource Development Institute (SRDI), Noakhali. Soil pH was determined with the help of a glass electrode pH meter; the soil–water ratio was maintained as 1:2.5 according to Jackson (1962). To measure electric conductivity, EC1:1 method was used (Smith and Doran 1996). Organic carbon in soil sample was determined volumetrically by wet oxidation method of Walkley and Black (1934). The underlying principle is to oxidize the organic matter with an excess of 1 N K₂Cr₂O₇ in presence of conc. H₂SO₄ and to titrate the residual K₂Cr₂O₇ solution with 1 N NH₄FeSO₄. The amount of soil organic matter was calculated by multiplying the value of organic carbon with the Van Bemmelen factor, 1.724 (Piper 1950). The total nitrogen in the soil was determined by Kjeldahl method by digesting soil sample at 390 °C in a digestion tube with 5 ml 98% conc. H₂SO₄ and 1.0 g catalyst mixture (K₂SO₄:CuSO₄·5H₂O = 10:1) by a digestion unit (Page et al. 1982).

Available phosphorus was extracted from the soil by shaking with 0.03 M NH₄F–0.025 M HCl solution at pH < 7.0 following the method of Bray and Kurtz (1945). The phosphorus in the extract was then determined by developing a color using ammonium molybdate-ascorbic acid solution to the extract. The intensity of blue color was measured at 890 nm wave length in spectrophotometer and available P was calculated with the help of standard curve. Potassium was determined by using flame photometer (Black et al. 1965).

Available S content of soil was determined by extracting the soil with S extracting solution. The extractable sulphur content was determined by developing turbidity by adding acid seed solution [150 ml conc. HNO₃, 550 ml glacial acetic acid and 7 ml sulphur stock solution-1 (1000 mg/L S) was mixed added water to volume 2 L] and turbidimetric reagent [20 g polyvinylpyrrolidone and 300 g BaCl₂·2H₂O up to 2 L volume with distilled water]. The intensity of turbidity was measured by spectrophotometer at 535 nm wave length following the extraction-turbidity method described by Fox et al. (1964). For measuring boron, at first nitrogen digester should turned on and was adjusted it to 150 °C. Then soil was digested with 0.01 M CaCl₂ solution in the ratio 1:2 into clean and dry digestion tubes with glass stopper in each. After first bubble, the temperature setting was reduced to 110 °C and boiled for exactly 5 min from the time was start. The digester was turned and placed the tubes in a vessel with cold water for 15 min and filtered on a dry filter into a dry plastic bottle and then Transferred 2.0 ml undiluted filtrate into another dry plastic bottle, added 4 ml buffer solution and 4 ml Azomethyl-H reagent and mixed. After 30 min the absorbance was measured at 420 nm on a spectrophotometer and calculated by using a standard curve (Petersen 2013).

Field observation for SHC preparation

In 2002 a group of Northern Rivers Region farmers develop a soil health monitoring tool named Northern Rivers Soil Health Card (NRSHC), based on United States Department of Agriculture (USDA) format. A major value of the exercise was the farmer involvement that allowed the card to be customized to fit the needs of the individual using it. It is simple and effective extension tool for soil quality monitoring using simple rating system that people can use to evaluate and monitor soil health or compare practice effects on soil health. In this process farmer participation was taken, which has facilitated engagement and increased awareness of soil health issues and enabled farmers to self diagnose and solve their own problems (Lobry de Bryun and Abbey 2003). To prepare SHC, soil health indicator of NRSHC method was used in this study. To prepare SHC ground cover percentage were assess using coat hanger quadrate, which put into the ground at random manner and estimated the proportion of bare soil within the frame and subtracted from 100% (NRSHC 2002). For the infiltration test, the infiltrometer tube was pushed to the soil up to 1–2 cm into the soil, avoiding cracks and other holes in the ground. The tube was filled with water and the time was recorded by stopwatch how far the water level had fallen up to 5 min. The rate of infiltration then counted by ratio of water level decrease and time elapsed to infiltrate the total water (NRSHC 2002). For counting the diversity of macro life, the coat hanger quadrate was put on the ground at the undisturbed area and avoid the movement of varieties of soil animals such as ants, beetles, spiders, slaters, millipedes, mites and others were noted (NRSHC 2002). To measure the root development 15 cm square hole of soil surface was cut from the ground. The soil was lifted out as one block placing on the plastic sheet for observing the plant root and recorded on the card (NRSHC 2002). For observing soil structure, a handful of soil away from the surface of the block was dug up. The size and arrangement of the soil ‘aggregate or crumbs’ were examined under firm finger pressure (NRSHC 2002). To examine the crumbs stability 3 or 4 pea-sized soil crumbs were taken from 5 cm depth for avoiding small stones. The crumbs were merged into 125 ml water at a small wide mouthed jar for 1 min. After 1 min the crumbs were broke apart or stay intact (NRSHC 2002). To count the earthworm content, the total soil block was broken into small crumbs for observation if any worms were found into a jar. Any worm that was longer than 25 mm recorded on the sheet and let them return to the hole (NRSHC 2002). To measure soil pH, two small samples of soil were taken from the side of the hole-one from 5 cm and another from 15 cm depth. These samples were color matched with pH kit. Leaf color and plant growth crop, trees or pasture at the soil test site were observed visually (NRSHC 2002). Organic matter was determined in two soil sample collected from the surface (topsoil) and 25 mm (subsoil) depth. The soil color from the two depths was compared. When the surface color similar to the subsoil color the smell of the soil sample was taken for differentiate. A sweet earthy smell indicates the soil was rich in organic matter (SQCDG 1999). For the seedling emergence about 100 sections of seeded rows were measured with tape and the height of several plants within the row was measured randomly (PNSQCG 2004). Drainage capacity was examined from the farmers interview that how many days rainwater needs to erase from the field totally after a heavy rain such 2,3,5 or 7 days. Below 1 day it prefers good, 2–3 days indicates the medium and 5–7 days indicates the poor drainage capacity of the field (NRSHC 2002).

Data interpretation and analysis

Soil quality determination using laboratory assessment

Soil electrical conductivity (EC) is a measurement that correlates soil properties that affect crop productivity including soil texture, cation exchange capacity, drainage conditions, organic matter level, salinity and sub-soil characteristics. On the other hand, the electrical conductivity of soils varies depending on the amount of soil moisture. Generally EC has good relationship with soil particle size and texture (Grisso et al. 2009). The EC of the samples ranges from 0.79 to 6.67 dS/m with a mean of 2.75 dS/m (Table 2).

Organic matter (OM), an important properties derived from the decomposition of plants and animals. A wide variety of organic carbon in soils range from freshly deposited litter, i.e. leaves, twigs, branches, etc. to highly decomposed forms, i.e. humus (Schumacher 2002). OM defines the total carbon storage, fertility and stability of a particular soil mass (Brady and Weil 2005). Potential benefits of increased microbial biomass and their activities includes; increased soil aggregate formation and stability, enhanced plant litter decomposition, increased nutrient cycling and transformations, slow-release storage of organic nutrients, and pathogen control (Lagomarsino et al. 2009; Nautiyal et al. 2010). Organic matter contents of the studied field were found 0.34–2.54% which indicates low to medium percentage of OM.

Soil nutrients are the indicator of soil total productivity and agrochemical quality. Their levels and transformations are critical to soil health (Kibble-white et al. 2008). Organic C and N controls soils microbial catalytic potential and indicates the early warming of management effect on organic matter (Brady and Weil 2005). Soil organic C and total N of the studied samples varied from 0.20 to 1.48% and 0.02 to 1.12%, respectively which are very low.

Physical observation and preparing Soil Health Card (SHC)

Comparison among traditional and laboratory analysis

From the scoring of studied parameters, it is found that the soil quality is medium according to laboratory analysis (Table 3). Here it should be noted that the scoring of soil chemical parameters were conducted according to Bangladesh Agricultural Research Council (BARC) fertility standard (Hassan et al. 2012), and according to the SHC soil quality of the studied fields is also medium except Field 1 (Table 4). The comparison among the two methods is presented in Fig. 2. Nevertheless it can be said that this Soil Health Card (SHC) assessment is truly representative and may be an alternative for laboratory assessment method.

Benefits of using Soil Health Card (SHC)