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Runoff and Soil Loss in Trinidad under Different Crops and Soil Management¹

ABSTRACT

Erosion caused by some of the farming practices on the major soil type (Orthoxic Tropudult) in the northern mountain range in Trinidad was assessed by measuring the runoff and soil loss from maize (Zea mays L.) and cowpea (Vigna unguiculata L. Walp) plots on 11, 22, and 52% slopes with and without tillage during the wet seasons in 2 consecutive years. The total rainfall for each of the three periods over which the experiments were conducted was 38.8, 22.4, and 82.5 cm, respectively.

At the lower levels of rainfall there was generally a significant increase in soil loss (but not runoff) from the bare plots with an increase in slope from 11 to 22 to 52%; but a nonsignificant increase in both runoff and soil loss from the cropped plots. At the higher rainfall level, there were significant increases in soil loss from the bare and both of the cropped plots with an increase in slope from 11 to 22% only.

The effect of tillage of the 22% slope on runoff and soil loss seems to have depended on the level and distribution of the rainfall and on the crop type. When rainfall is low, no-tillage does not significantly affect runoff or soil loss, but it significantly (P = 0.05) reduces soil loss from bare plots if there are intense storms. At the highest rainfall level, no-tillage still resulted in high soil losses (28 to 55 t/ha) and maize and cowpea (particularly maize) were less effective than at lower rainfall in reducing soil loss. Because of the high level of rainfall experienced in these hills the bare soil should not be exposed in the wet season and the clean cultivation of maize and cowpea in the wet season should not be recommended for slopes >11%.

¹ Contribution from the Dep. of Soil Science, The University of The West Indies, St. Augustine, Trinidad.

² Senior Lecturer and Research Fellow, respectively.

Received for publication February 18, 1982. Accepted for publication July 16, 1982.