Experiment 5DATA AND OBSERVATIONSTable 1: Effect of Sand on <strong>Soil</strong> <strong>Moisture</strong><strong>Soil</strong> Sample50% <strong>Soil</strong> Sample +50% Fine SandInitial soil moistureElapsed time when 1 cm water was addedElapsed time as added water reached sensorTime for water to travel 4.5 cm to sensorMaximum soil moistureTime required to reach maximum %<strong>Soil</strong> moisture at end of 5 daysPROCESSING THE DATA1. Which sample showed the greatest change in soil moisture over the 5-day period?2. How does soil particle size influence soil moisture?3. How is soil moisture important?EXTENSIONS1. Repeat the investigation for different soil types, soil taken from different locations, or soiltested at different depths.2. Investigate the effect of adding garden compost in place of fine sand to your soil sample.5 - 4 STEM with <strong>Vernier</strong> and LEGO MINDSTORMS NXT
Managing Garden <strong>Soil</strong> <strong>Moisture</strong>Experiment6Compost, aerobically decomposed remnants of organic materials, is commonly mixed into soil toimprove soil fertility and water holding capacity. Grass clippings, leaves, sawdust, kitchen refuse,wood ashes, garden refuse, and shredded newspapers are just some of the common materials thatare composted.Mulch, in contrast, is placed on the soil surface. Mulch affects soil moisture by slowingevaporation, reducing weed transpiration, and reducing runoff. Grass clippings, leaves, sawdust,wood chips, straw, shredded newspapers, and compost are common materials used as mulch.Inorganic mulches, such as plastic sheeting, rocks, and gravel are also widely used.Commercial water absorbing polymers, such as <strong>Soil</strong> Moist, Stockosorb ® , and Terra-Sorb,are water management tools that can reduce evaporation, water runoff, and soil erosion whenmixed into soil.In this experiment, you will investigate the ability of a soil sample to retain moisture with andwithout the addition of a surface layer of mulch.OBJECTIVESIn this experiment, you will• Learn to use a <strong>Soil</strong> <strong>Moisture</strong> Sensor.• Determine the volumetric soil water content of a soil sample.• Investigate moisture retention with and without mulch.• Gain increased understanding of the role of soil moisture in ecosystems, watersheds, andthe water cycle.MATERIALScomputerMINDSTORMS Edu NXT v2.0 software<strong>Vernier</strong> NXT Sensor Adapter<strong>Vernier</strong> <strong>Soil</strong> <strong>Moisture</strong> SensorNXT cableLEGO NXT Intelligent Brick withrechargeable battery and AC chargerfinely shredded wood mulchfine sandpan or traycut-off, 2 L plastic bottlewatersprinkling can or spray bottlePROCEDUREPart I Without Mulch1. Obtain a cut-off, 2 L bottle with holes in the bottom and a slot in the side. This will hold yoursand sample. The soil moisture sensor will go into the side slot. Place the bottle in a tray tocollect any water draining out.2. Fill the bottle with sand at least 10–12 cm deep. Insert the <strong>Soil</strong> <strong>Moisture</strong> Sensor into the slot.The sensor should be about 4–5 cm below the surface of the sand. Press down on the sandalong either side of the sensor with your fingers. It is important that the sand be fairly wellcompressed for good sensor readings.STEM with <strong>Vernier</strong> and LEGO MINDSTORMS NXT 6 - 1