Soil organic carbon is the basis of sustainable agriculture. Higher soil organic carbon promotes soil structure or tilth meaning there is greater physical stability. This improves soil aeration (oxygen in the soil) and water drainage and retention and reduces the risk of erosion and nutrient leaching. water holding capacity is the amount of water that a given soil can hold for crop use. Water holding capacity is important to soil health. Soils that can retain a balanced amount of water are able to nourish crops and keep soil organic matter alive. 

Objectives :

1. To study the effect of organic carbon on water holding capacity of soil.

2. To study the effect of organic carbon on crop yield.

3. To check the effect of organic mulching on the crop yield.

Need of project:

The organic carbon of soil is decreased leading to low microbes in soil which causes high demand of fertilizers and low water holding capacity of soil. Hence, the demand of water is increased leading to higher pollution and ecological imbalance.  


Determination of water holding capacity of soil

  1. 100 g of dry sample was taken.
  2. The funnel was set with filter paper on measuring cylinder.
  3. The sample was added on the filter paper. Then 200 ml water was added into the sample.
  4. The sample was kept for 20 minutes and the reading of water retained in measuring cylinder was taken.
  5. Then the water holding capacity of soil was determined by using following formula.

Water holding capacity = {(Total water added-Water retained in the measuring cylinder/Dry weight of sample}×100


Weight of soil=100 gm
Total water = 200ml
Water retained in the measuring cylinder = 110ml

Calculations –

Water holding capacity of black soil = {(200-110)/100}×100 = 90%

Fig. Determination of water holding capacity of soil

07/02/2022 – 25/02/2022

Collection of soil and preparation of beds

The experiment is to be carried out in beds of 2×2 ft. For this, bricks and black soil were collected from the nearby Vigyan Ashram. Measurements for bed preparation were taken with the help of tape. After that 9 beds were prepared for the experiments.

Fig. Preparation of beds

Qualitative Analysis –

Qualitative analysis uses subjective judgment based on non-quantifiable data.

Determination of Organic Carbon by O.C. kit

The O.C. of black soil determined by O.C. kit. There was variations in the O.C. of soil. It ranged from 0.8 -1 but the exact value of O.C. was not received.

Fig. Determination of O.C by OC kit

Quantitative Analysis

Quantitative analysis is any method used for determining the amount of a chemical in a sample. Calculating exact value of O.C. in soil.

Determination of Organic Carbon by Walkley- Black Method


  1. 500-mL conical flasks.
  2. 10-mL pipette.
  3. 10-and 20-mL dispensers.
  4. 50-mL burette.
  5. Analytical balance.
  6. Magnetic stirrer.


  1. H3PO4, 85%
  2. H2SO4, concentrated (96%)
  3. NaCl, solid
  4. Standard 0.167M K2Cr2O7:- Dissolve 49.04 g of dried (105°C) K2Cr2O7 in water and dilute to 1 L.
  5. 0.5M Fe2+ solution: Dissolve 196.1g of Fe (NH4)2(SO4) •6H2O in 800 mL of water containing 20 mL of concentrated H2SO4 and dilute to 1 L. The Fe2+ in this solution oxidizes slowly on exposure to air so it must be standardized against the dichromate.
  6. Ferroine indicator: Slowly dissolve 3.71 g of ophenanthroline and 1.74 g of FeSO4•7H2O in 250 mL of water.


  1. Weigh out 1.00 to 2.00g dried soil and transfer to a 500-mL conical flask.
  2. Add 10 ml K2Cr2O7 solution by means of pipette.
  3. Add 20 mL. H2SO4 of concentrated by means of a dispenser and swirl gently to mix of the flask out of the solution.
  4. Allow to stand for 30 min. The flasks should be placed on an insulation pad during this time to avoid rapid heat loss.
  5. Dilute the suspension with about 200 mL of water to provide a clearer suspension for viewing the endpoint.
  6. Add 10 mL of 85% H3PO4, using a suitable dispenser, and 0.2g of NaCl. The H3PO4 and NaCl is added to complex Fe3+ which would interfere with the titration endpoint.
  7. Add 10 drops of Ferro in indicator.
  8. Titrate with 0.5 M Fe2+ to a burgundy endpoint. The color of the solution at the beginning is yellow-orange to dark green, which shifts to a turbid grey before the endpoint and then changes sharply to a wine red at the endpoint .
  9. Run a reagent blank using the above procedure without soil. The blank is used to standardize the Fe2+ solution daily.

Formula –

O.C={(B-S)×M of Fe2+×12×100}/4000


  1. where B = mL of Fe2+ solution used to titrate blank
  2. S = mL of Fe2+ solution used to titrate sample
  3. 12/4000 = Mili equivalent weight of Carbon.


the experiment was performed for 4 times to determine the Organic Carbon of black soil. The calculations are as follows: titration reading Titration with sample reading % O.C.
Table 1 : calculation of % O.C.of soil

there was variations in the o.c. of soil. It was due to the differences in procedure. The phosphoric acid was not used in first 3 times. So, the value of o.c. was not accurate. The experiment was again performed then got exact value of o.c. of black soil, it was 0.96%

Fig. Determination of O.C by Walkley-Black method

The O.C. of compost was determined by walkley- black method and its 22.2%.

After the determination of O.C. of soil compost, to increase the O.C. of soil theoretical calculations were done by following formula.

O.C={[weight of soil×O.C)+(weight of compost×O.C.)]}/Total weight

% O.C. of soilAmount of compost needed to add for 100 gm of soil
Table 2: Amount of compost added in soil
Fig. Mixing of compost with soil



After mixing of compost with soil beds were filled with mixed soil. And then sowing of spinach seeds were done with the help of khurpi at the spacing 15×15.The seed rate was 3 seeds per hole. At final water was given to each bed.

Fig. Sowing of spinach

Tying of shadenet –

For tying of shadenet, the shadenet was collected from polyhouse of Vigyan Ashram. Also the rods were collected from scrap yard. The rods were cut to the desired length with the help of hand grinder.

Fig. Cutting of rod and tying of shadenet


Mulching of agricultural waste:

Material used for mulching : Soyabean Straw

After collection of Soyabean straw, mulching on spinach beds of thickness upto 1 cm were done. Out of 9 beds, 3 beds were mulched.

Fig. Mulching on spinach bed

26/02/2022 – 28/03/2022

Irrigation application to the Spinach beds:

DateWater application( with mulching)Water application (litres)(without mulching)
Total water7699.5
Table. Irrigation application

From above table, it is seen that quantity of water required for the beds of with mulching is less than beds of without mulching.

fig. Application of water to the bed

At the beginning , due to more application of water to the black soil,it caused water logging. so, they were germinate late.

LOD (Loss on drying) of black soil was calculated to estimate irrigation application to the spinach. Following are the calculations of LOD.

TimeWithout mulchingWith mulching
Table: Calculations of LOD in %


Organic carbon determination

After more than a month, organic carbon of black soil was calculated by walkley black method. Following are the reading of it.

Fig. Organic carbon determination
Sr no.Blank titration readingTitration with sample readingO.C%
Table: Calculations of organic carbon


Harvesting of Spinach:

Fig . Spinach harvesting

Morphological characteristics of spinach:

Beds without mulching:

O.C%Average number of leavesAverage leaf sizeAverage plant height
Table. Morphological parameters of spinach beds without mulching

Beds with mulching

Fig. Beds with mulching
O.C%Average number of leavesAverage leaf sizeAverage plant height
Table. Morphological parameters of beds with mulching

From above table, it is seen that, the maximum average number of leaves are found in bed in which organic carbon is 3% followed by bed in which O.C is 1%. Maximum average leaf size is found in bed which have O.C 3% and maximum average plant height is found in that bed which have organic carbon 3% and it is followed by bed of O.C 1%.


Determination of water holding capacity of soil:

To check the effect of organic carbon on water holding capacity of black soil, it is again determined. The initial water holding capacity of red soil was 90%. After harvesting of spinach, the water holding capacity of soil is determined and it was found that it is increased with increased in level of organic carbon.

Organic carbon %Increasing % of water holding capacity
Increasing % of water holding capacity


  1. Increase in the growth parameters of spinach crop was noticed in all beds with increase in level of organic carbon.
  2. The maximum number of leaves, plant height and leaf lengths were found in bed which have organic carbon 3%.
  3. It was found that the increased in level of organic carbon increased in water holding capacity of soil. It It is increased by 22% and 34% with increase in organic carbon content by 1% and 2% respectively
  4. Better crop yield and minimum quantity of water requirement is found in beds of mulching compared to beds of without mulching. About 23% less water required for the beds of with mulching.
  5. The result of the study have demonstrated that crop production in soil and water holding capacity of soil could be improved by adding compost to the soil.