Root distribution, standing crop biomass and belowground productivity in asemidesert in Mexico

In a semidesert community in Mexico (Zapotitlan de las Salinas, Puebla) the vertical distribution of roots and root biomass was estimated at 0-100 cm depth on two sampling dates, November 1995 (wet season) and January 1998 (d ry season). Root productivity at 7 to 14.5 cm depth was estimated with the in-growth core technique every two months from March 1996 to February 1998. The relationship between environmental factors and seasonal root productiv ity was analyzed. Finally, we tested the effect of an irrigation equivalent to 20 mm of rain on root production. Seventy four percent of the total num ber of roots were found at 0-40 cm depth. Very fine roots (< 1 mm diameter) were found throughout the soil profile (0-100 cm). In contrast, fine roots (1-3 mm diameter) were found only from 0-90 cm depth, and coarse roots (> 3 mm diameter) from 0-60 cm depth. The root biomass was 971.5 g m(-2) (S.D. = 557.39), the very fine and fine roots representing 62.9% of the total. T otal root productivity, as estimated with the ingrowth core technique, was 0.031 Mg ha(-1) over the dry season and 0.315 Mg ha(-1) over the wet season . Only very fine roots were obtained at all sampling dates. Rainfall was si gnificantly correlated with very fine root production. The difference betwe en fine root production in non-watered (0.054 g m(-2)) and watered (0.429 g m(-2)) treatments was significant. The last value was the same as that pre dicted for a rain of 20 mm, according to the exponential model describing t he relation between the production of very fine roots and rainfall at the s ite.