THE TYPES of grassland agriculture in Puerto Rico are linked closely with the rainfall belts: The driest belt, the extreme southwestern part, receives from 25 to 35 inches annually of rainfall. This is about the same range of precipitation as between Nebraska City and Grand Island, Nebr. But the similarity ends there: Instead of luxuriant, level Nebraska fields, rich grass, rounded haystacks, groves, dark soil, and sectionized roads, with two or four large homes at the crossroads, there are here brown, highly calcareous soils, cacti and spiny shrub-covered hills, valleys of guineagrass pastures for the hundreds of native oxen, and a few ranch houses along oxcart roads. This is the "Great Plains" of Puerto Rico.
A typical ranch here reminds one somewhat of Arizona and New Mexico and some other Western States. It consists of a small group of ranch buildings surrounded by several thousand acres of fenced and cross-fenced, undulating, hilly grass and cactus pastures. One rancher may own 2,000 to 3,000 head of cattle and hire 30 or more hands.
The irrigated lands, with green, succulent sugarcane on all land that is not charged with alkali and saline salts, are in sharp contrast with the and hills nearby. The soils in this area are mostly high in calcium and other plant nutrients, and the grass appears to be fairly high in phosphorus, calcium, carotene, and crude protein, as indicated by the healthy appearance of the livestock during an average season.
In this area and in the belt that gets about 10 inches more of precipitation,the common practice is to put about 60 head of cattle in a 60- or 70-acre pasture for several days, then change them to another pasture. The yearly carrying capacity of the land ranges from about 2 acres a head on the nearly level alluvial fans to about 5 or 6 acres a head on the rolling uplands. The carrying capacity varies considerably from year to year and from place to place, depending upon the rainfall, the care of the pasture, and the kind of grazing. About 20 inches more of rain a year would nearly double the carrying capacity in districts receiving from 25 to 50 inches of precipitation.
Pastures that have been freed of weeds such as cacti, zarzarilla, and guayacan blanco have a much higher carrying capacity than the weed-infested pastures, Zarzarilla spreads rapidly, and several stockmen report that the animals that eat it may lose some of their hair and manes. Guayacan blanco grows mostly on the shallow soils derived from limestone in both the and and subhumid districts. The pollen from this plant seems to irritate the eyes of the animals and some ranchers report that it causes blindness in cattle.
The carrying capacity of the range depends somewhat on the management of the livestock. Cattle that are badly infested with ticks require more grass and a larger area to graze in order to be in as good a condition as the nearly tick-free animals. Most of the so-called native cattle and the zebu strains are more or less immune to tick fever, but if they are infested with ticks their strength is sapped, a point of vital importance during the dry periods when pastures are overgrazed. In places along the and southern coast, hundreds of cattle die of starvation during a long drought like the one in the winter of 1930-31. Generally speaking, the first to die are those most heavily infested with ticks.
The approximate acreage of pasture land in this area (25 to 45 inches of precipitation), according to the 1940 Federal census, is 143,000 acres. Many of the pastures have been planted with guineagrass, which grows 1 to 6 feet high and seems to be much more nutritious than grass grown in the humid sections. Cattle born and raised on grass from the neutral or calcareous soils in this district are generally in better condition than animals born and raised on the coarse, less nutritious grass from acid soils of the humid districts.
Bermuda-grass is another important grass in this district. It is tolerant to alkali and saline salts and is grown largely on the level lands near the coast. Bermuda-grass and horquetilla morada, or Mexican bluegrass, a fine-leaved grass, are propagated naturally over the and and semiarid districts.
Mexican bluegrass is fairly nutritious, but good stands of it often are plowed under, and guineagrass is planted. The general procedure is to plant bunches of guineagrass in rows. It is often interplanted with corn during the rainy season (summer), but in some places the seed is planted. The seeds, however, may lie dormant in the soils for some time before they receive enough moisture for germination. In a few years after planting, the guinea-grass will spread if the soils are deep and well drained and the area receives considerable moisture, but in the shallow soils or on dry hillsides the guinea-grass bunches do not readily stool. During drought periods, this grass becomes brown and dry, but it still has enough strength. to keep the cattle alive. Within a few days after a rain the grass in the previously brown, baked pastures becomes green and fresh. Cattle may be completely hidden by the tall, dense guineagrass in some pastures. Fertilizers would probably not greatly increase the yields here.
In the 45- to 55-inch rainfall belt the type of agriculture is quite different from that in the more arid, thinly populated regions. The ever-increasing population pressure in Puerto Rico (there are nearly 600 persons to the square mile) forces the cultivation of steep hillsides, so steep in places that it is dangerous to walk. In this rainfall belt the population is dense, and the precipitation is sufficient to tempt the small farmer or jibaro to plant clean-cultivated crops such as corn, beans, tobacco, and pigeonpeas. Generally, rainfall is insufficient for rapid plant growth. When the rainy season starts, the intense showers wash the soil down the hillside before any vegetation has a chance to retard the flow of the water. The amount of erosion is not so great as in the clean-cultivated mountain areas of some of the tobacco districts, but the harm resulting from the erosion is more lasting. Eventually much of this land becomes unproductive for cultivation, it is abandoned, and grass takes over. Small gullies form before the slowly growing pasture grasses can become established well enough to withstand the lashing rains. This land erodes severely for a year or two, but finally the grass thickens and erosion is arrested.
The management of the approximately 63,000 acres of grass pastures in this zone is difficult. The fields are small, and the owners cannot afford to buy fertilizers and take care properly of the pasture land. The pastures are used for goats, hogs, and local work oxen and dairy cows. As soon as erosion scars are healed, the chances are that the land will be plowed again and used for subsistence crops; erosion starts, and the circle repeats.
The 55- to 75-inch rainfall belt has approximately 184,000 acres of pasture. Proper fertilizer and better grasses would improve the pastures greatly. Many farms are planted to cultivated crops year after year on slopes of 60, 80, and 100 percent. Erosion is rapid, but vegetation grows so quickly and densely that the force of the running water is checked before it does destructive washing. In fact, some washing is desirable, because it keeps the soil young and more plant nutrients are available.
Under a heavy vegetation the soil granules are bound together by the millions of plant roots. Then, too, most of the soils of the island are derived from tuffs and shales, which contain a small amount of quartz. Therefore the weathering of these rocks produces a soil that is high in permeable clay, medium low in silt, and low in sand. Because the soils are without either a high content of silt, which may melt away like sugar under a tropical shower, or the abrasive effect of tons of sand plowing down the hillside, erosion in many places only keeps pace with the rapid decomposition and disintegration of the rocks. The moist, hot climate makes an ideal condition for the rapid weathering of rocks; also, the runoff water on most farms on Puerto Rico has a steep but short course before it empties into grass-covered, healed-over ravines or rock-bottomed small streams.
The Puerto Rican farmer has prevented soil loss by building brush and rock terraces along the contours of the steep slopes and by planting guinea-grass in hedgelike strips at irregular intervals on the steep hillsides. In the tobacco area, the farmers dig short checkerboard ditches along the hillsides. The bottoms of the ditches often rest on solid rock, thus eliminating conditions favorable for gully erosion. If any soil reaches the ditches, it flows to the ocean, but because of the many small squares surrounded by ditches, the water does not have a chance to collect much soil before it runs into a ditch. When sheet erosion has reduced the depth of the surface soil to such an extent that only unprofitable yields can be obtained, the land is usually abandoned. Grass, weeds, and brush start growing and the soil washing stops; the fast soil-forming process soon builds a new soil, to be cultivated again within 2 or 3 years.
The belt that has more than 75 inches of rainfall includes a larger portion of Puerto Rico than any other. It has approximately 228,000 acres of pasture land. It produces a great diversity of crops nearly every type of product grown on the island : Corn,beans, yucca, yautia, sweetpotatoes, pigeonpeas, names, oranges, bananas, plantain, mangoes, breadfruit, papaya, alligator-pears, coffee, grapefruit, pineapples, sugarcane, tobacco.
The rainfall here is sufficient for all crops but the high precipitation so necessary for the existence of the plants has had a destructive effect on soil, people, and stock. In the high rainfall areas, most of the soils have been leached to the extent that they want calcium, phosphorus, and magnesium. The calcium-phosphorus deficiency is critical in part of this rainfall belt. Only a few of the small landowners use fertilizer or manure to offset the loss of these mineral elements, and the plants produced, whether grains or grasses, do not have the food values necessary for the development of bones, teeth, and the physical well-being of the animals and people who eat them. Rickets and poor teeth are common in the mountains. The stock that graze on grasses of the neutral or alkaline soils of the and regions have larger bones, smoother hair, and better general appearance than those pastured in the moist mountains, where acid-leached soils are dominant and the grass is tall and dense. Calcium-phosphorus deficiency is becoming serious in this area. Phosphorus fertilizer should be beneficial, especially on the red Lateritic soils.
In places the tall, thick grass is so low in nutritive value that cows do not produce sufficient nutritive milk to produce normal calves. In contrast to these sites of leached Lateritic soils, nearby Rendzina soils, black, calcareous, productive, and developed from soft limestone, produce nutritive grass, and the cattle pastured on these productive soils have the same appearance of health as those in the and regions. Naturally, the boundary between these two contrasting soil sites is sharp, as is also land use and vegetation. The jibaros say the grass from the limestone areas is "sweet" and the stock like it much better than the grass produced on the red soils. They also say that pigeonpeas produced on the black soils and on the shallow brown soils are better and yield much more than those planted on the deep, red, acid soils.