Michael Glenn Hickey of the University of Texas studied various devices for increasing potato production in West Texas (THE EFFECT OF SOIL TYPE ON STOLON NUMBER,TUBER INITIATION, AND TUBER VOLUME IN IRISH POTATOES, 1977). “Potatoes in West Texas are grown for an early retail market which requires harvesting prior to maturity. Early tuber set would allow more time prior to harvest for tuber bulking. An extended period of tuber bulking would result in higher numbers of marketable tubers, thus an increase in yield. A knowledge of some of the factors influencing tuber initiation would aid in the understanding of early tuber set.”
Early emergence, of course, helps. “The percentage of plants emerging is shown to decrease with decreasing clay content in the soil. Plants in all three soils failed to show any marked differences in early emergence, up to 17 days after planting. From 17 to 31 days after planting the differences in plant emergence were more significant and the distinct textural difference appeared.”
But the friability of the soil is only part of the reason for early emergence: potatoes are strong enough to push their way through even hard clay. “The textural differences can be attributed to the differing moisture relations in the three soil types. Increasing the clay content results in an increased moisture retention. Moisture that was held in the proximity of the seed piece would aid in increasing the percentage of emergence. The water retention capacity of the Patricia soil was extremely low. Water moved through the soil and little was retained around the seed piece. Thus a drying out effect between waterings existed in the Patricia fine sand that was not as evident in the Amarillo and Pullman soils. The drying out of the soil between waterings would affect any weak seed pieces. This would result in poor emergence of plants, especially during the later period of plant emergence.”
Raising temperatures in greenhouses are not necessarily a good idea, once summer temperatures have arrived: high temperatures can reduce iron uptake and also greenhouse effects can alter the moisture content in the soil: “Plants growing outside of the greenhouse exhibited a higher percent emergence than those inside the greenhouse. Better water relations outside the greenhouse could possibly account for the difference. Lower relative humidities outside of the greenhouse would permit a more uniform drying of the soil, this would compensate for the rapid water movement in the sandy soils and permit a more even moisture distribution for the three soils. High soil temperature, above 21 C, has been shown to inhibit plant growth of potatoes (Somnerfeldt and Knutson, 1968).”
All this goes to show the reasons why higher tuber production is achieved through mounds, and the grow towers that are typically used for the cultivation of potatoes: under such conditions, moisture is easily maintained neither high or low, and temperature is also regulated. Other species that rely on similar constancy for their crops rely on mounds (such as ants farming fungi), and human farmers would do well to emulate them.