QUIROGA: a MEXICAN MUNICIPIO — BRAND 



127 



though shallow plowing does not mix the tepetate 

 with the uppei- horizons, the denudation of years 

 has deposited upon the lowlands quite a bit of poor 

 soil derived from the tepetate of the slopes. In 

 general, the soils range from very deep near the 

 lake to e.xtremely thin on the upper slopes, and 

 have an average thickness of only a few inches. 



Red is the dominant color of Quiroga soils. This 

 red varies from brick red, through reddish brown, 

 to a yellowish red. There are many places carry- 

 ing such names as Cerro Colorado and Tierra 

 Colorada in the region. The most common shade 

 of red is reddish brown or cafe, which probably 

 constitutes the color of moi'e than three-fourths of 

 the soils. Normally, dark reddish brown or caje 

 obscuro is a good soil, light reddish brown or cafe 

 is intermediate in value, and the red {charanda) 

 and yellow (amarilla, tupura) soils are poor. The 

 reddish color is derived from unhydrated iron 

 oxides and indicates good drainage and aeration. 

 The yellow soils are restricted to the highlands, 

 commonly in pine-forested areas, as on the slopes 

 of Azul, Chmo, and Tzirate, and commonly rep- 

 resent hydrated iron oxides. These yellow soils 

 usually are poorly drained and contain much 

 organic acid. There are areas in the oak-pine- 

 madroiio a-ssociation on the upland slopes where 

 the duff and mull have produced rich but shallow 

 soils known locally as tierra negra or prieta and 

 tierra tocura (from tocuz, an oak). These soils are 

 seldom cultivated. Beneath the forest matting, 

 especially at the higher elevations, are poor 

 grayish soils. 



The soil varies from heavy, dense compact 

 clays, through the crumb-structured medium- 

 heavy clay loams, to the light open sandy loams. 

 The heavy clays are adhesive, form large hard 

 clods, and are hard to work. The clay loams are 

 normally plastic, form hard clods, and are not too 

 hard to work. The sandy and silty loams are not 

 plastic at all, and are light and easy to cultivate. 

 The tepetate and the clays immediately above it 

 are practically impermeable, but the less dense 

 clays and the loams have a high percentage of 

 porosity (commonly 45-53 percent). The water- 

 holding capacity of the clay loams is fairly high. 

 Most of the cultivated soils have no pebbles, little 

 gravel, from 35 to 50 percent sand, 15 to 30 per- 

 cent silt, and 25 to 50 percent clay. The mean 

 probably runs 41 percent sand, 36 percent clay, 

 22 percent silt, and 1 percent gravel. Clays and 



clay loam dominate the soils of Quiroga. The silt 

 content is too low and the clay content is too high 

 for good soils. 



Mineral soils predominate in the Quiroga area. 

 The originally basic rocks of the area have decom- 

 posed into somewhat leached soils which are essen- 

 tially neutral, although the pH or acidity factor 

 usually runs between 6.6 and 7.0. Tliis falls with- 

 in the optimum range 6.5 to 7.2. In the oak and 

 pine-forested highlands the pH factor may drop as 

 low as 5 or 4, but on the slopes of infiltration and 

 the lowlands of deposition there are soils with 

 alkalinity up to 8. The very harmfid black alkalis 

 or tequesqyite have been fairly well leached out of 

 the soils, although percentages from 0.01 to 0.05 

 are common. The other harmful alkaline salts 

 such as sodium chloride and sodium sulfate are 

 also nearly negligible in the soils of the area. The 

 calcium carbonate content is rather low for a good 

 soil, but the available calcium is usually adequate. 

 Organic carbon, and organic material in general, is 

 definitely deficient in most of the soils. Available 

 nitrogen and potassium are deficient, but there 



Table 25. — Analyses of soil samples ' 



' The four analyses are considered to be representative of the majority of 

 the arable soils of the Quiroga area. Numbers 1, 2, and 3 come respectively 

 from the plain, lower slope, and intermediate slope of an upland valley in the 

 area (La Noria-Atzimbo). Number 4 is from the higher lake plain south of 

 Quiroga (La Tenerfa) and represents one of the longest cultivated soils in the 

 area. The soils were collected in June of 1945, and were analyzed in May of 

 1946 by technicians in the Soil Laboratory of the Direcciiin General de Agro- 

 economia, Comision Nacional de Irrigacion. The writers are much indebted 

 to the staff of the Comision Nacional de Irrigacion and to Undersecretary 

 of Agriculture, Alfonso Gonz41ez Qallardo. A background on the soils of 

 Mesico, and edaphology in Mexico, can be obtained from reports of Gonzalez 

 Qallardo (1941); Waltz (1942); Foglio Miramontes (1936); and Rodriguez 

 (1942). 



' P. p.m. = parts per million. 



iUV 



