Improving the quality of the urban land

Teresa Sauras, Núria Roca
Plant Physiology Division, Department of Evolutionary Biology, Ecology and Environmental Sciences, Biology Faculty, University of Barcelona

Sara Cabrero, Anna Rigol, Miquel Vidal
Analytical Chemistry Division, Department of Chemical Engineering and Analytical Chemistry, Chemistry Faculty, University of Barcelona


Urban land has very little capacity to retain water and nutrients to properly grow plants, and may contain contaminant substances, such as heavy metals. Good soil quality makes it possible to develop leafy green areas that improve the health of the population.


Improve the quality of the soil by adding biochar (an organic product that is recycled by transforming biomass).


  • Urban soil near you
  • Biochar
  • Recycling 33cl transparent plastic water bottles
  • Loose cotton
  • Cling film or aluminium foil
  • Water
  • Indicator paper to measure pH
  • Table with a pH scale
  • Kitchen scale

Steps to follow


CHOOSE a section of urban land and geo-reference it.


PREPARE a soil mixture with between 2% and 5% of biochar in terms of the weight of the soil.


CUT two bottles of water in half and, with the lid on, place the top half upside down.


STUFF loose cotton into the bottle neck so that water can get through, but not soil.


Above the cotton, FILL one bottle with just soil, and the other with a mixture of soil and biochar, until it is half way filled.


WEIGH THEM and WRITE DOWN the weight.


POSITION the half of the bottles filled with soil and soil-biochar, still with the lid at the bottom, inside the other half of the bottles.


GRADUALLY ADD water, soaking the surface until the water is roughly 1cm higher than the soil and the soil-biochar mixture.


COVER the upper part with cling film or aluminium foil to prevent the water from evaporating, and leave the soil in contact with the water for 24 hours.


REMOVE the lid and let the water drain for 48 hours.


REMOVE the wet cotton, so that the weight of the retained water is not taken into consideration.


WEIGH the part of the bottle containing the soil and the soil-biochar mixture again. The difference between this weight and the original weight allows you to calculate the percentage of retained water.


MEASURE the pH of the water, submerging the indicator paper into the water that has passed through the cotton into the other part of the bottle.


COMPARE the colour with those on the pH table to obtain the pH value.


COMPARE the results, both for the hydric retention and the pH, of both the soil and the soil-biochar mixture.


REPEAT the experiment with different quantities of biochar until you find the mixture that provides the best results for the chosen soil.

Data to collect

Les teves dades s'han enviat correctament.

Moltes gràcies!

Formulari incorrecte, revisa els camps en vermell

Geolocation, origin of the soil


PH Concentration

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