Synopsis Napiergrass, guineagrass, and paragrass responded strongly to annual applications of up to 800 pounds of nitrogen per acre. Protein content and protein yields increased up to the highest N level tested. Yields increased but quality of the forage decreased with length of harvest interval. Between 30,000 and 45,000 pounds of dry matter averaging about 9.5% protein were produced annually per acre.

Synopsis Grass yields responded strongly to yearly applications of up to 400 pounds of K per acre and at a slower rate to even higher applications. With 800 pounds of K, exchangeable soil K content was maintained and two‐thirds of the applied K was recovered in the forage. At the 1600‐pound rate, recovery in the forage was reduced but exchangeable soil K content was increased. K content of the forage increased with rates and with yields.

Yields of tobacco (Nicotiana tabacum L.) on three Ultisols in Puerto Rico increased with liming up to about pH 5.0. There was a highly significant inverse relationship between yield and exchangeable Al. Maximum yield was generally reached as exchangeable Al approached 0 and at base saturation values of around 60%. Yields on an Oxisol increased with liming to about the same pH and base saturation level, although only traces of exchangeable Al were found. Leaf analysis indicated that Mn toxicity was a probable factor in the Oxisol. Tobacco root growth, studied in one of the Ultisols, was directly affected by low soil pH. Al toxicity appeared to be the chief cause of restricted growth but Ca deficiency was a possible contributing factor.

Plantain roots decreased sharply with depth and distance from the pseudostem on 5 soils typical of vast areas in the tropics. Primary roots in the upper 15 cm of all soils decreased from an average of 111 cm/1,000 cm3 of soil at 0-30 cm from the pseudostem, to 29 cm/1,000 cm3 of soil at 60-90 cm from the pseudostem. At 0-30 cm from the pseudostem, roots decreased from 111 cm/1,000 cm3 of soil in the upper 15 cm of soil to 11 cm; 1,000 cm3 of soil at the 30-45 cm depth. No roots were present below 45 cm in any soil.

The effects of phosphorus applications on yields and phosphorus content of otherwise well-fertilized tropical grasses growing on three typical soils of the Humid Region of Puerto Rico were determined. Napier grass responded strongly in yield to applications of 150 pounds of P2O5 per acre yearly on both Múcara and Catalina clay soils at Orocovis. The phosphorus content of the forage increased with applications of up to 300 pounds of P2O5 per acre yearly on both soils. On the other hand, Napier, Guinea, and Pangola grasses, growing on a Fajardo clay formerly in moderately fertilized sugarcane for many years, did not respond in yield or phosphorus content to applications of phosphorus over a 5-year period. Various methods of determining "available" soil phosphorus did not give satisfactory results with these soils.