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Fertilizer Management with Drip Irrigation in an Oxisol¹

Oxisols are the dominant soils of the continental shields in the tropics under permanently moist and alternately wet and dry climates. Oxisols have a low cation exchange capacity, high permeability, but low available waterholding capacity. Some have a low pH, which can cause Al^3* toxicity to many crops. Together with erratic rainfall patterns, special management methods of soil-water and plant nutrients for Oxisols are yet to be carefully studied. The relatively recent development of combined high frequency irrigation and fertilizer techniques, "drip fertilization," may be one of the solutions for intensive production of food crops on Oxisols.

A drip irrigation system using porous plastic tubing was designed for a field experiment to study the feasibility and operational techniques of drip irrigation and fertilization management in a highly weathered, acid Oxisol (Coto clay). Green pepper (Capsicum annuum L.), ‘Blanco del Pais’ was the test crop. A randomized, completeblock design was chosen to compare different fertilization techniques. In addition to the check plot, the three other treatments were: fertigation (drip irrigation and drip application of N and K, banded P); drip irrigation with banded N, P, and K; and drip irrigation with broadcast N, P, and K. All treatments, except the control plot, received a total amount of fertilizer equal to 56.8 g of 10-10-10 commercially available fertilizer per plant and all treatments were uniformly drip irrigated according to pan evaporation data.

Different moisture profiles during the wet (June-November) and dry (December-May) seasons were observed. Nutrient movement profiles suggested that the distribution of fertilizer under drip irrigation depended on the method of fertilizer placement. Root development patterns indicated that more than half of the root system (dry weight) was developed in the 5 to 15 cm layer. More fibrous roots were developed toward the porous drip tubing which supplied moisture and nutrients. Yield were significantly different among all treatments during the dry season and the fertigation, broadcast, and control during the wet season. Yields from broadcast fertilizer treatments were 15.8% lower than from fertigation, and 12.3% lower than from banded fertilizer. The results of this research indicates drip fertigation can be a promising alternative to currently used water-nutrient management methods for Oxisols in the wet-dry tropics.

Key Words: Water management • Fertigation • Soils of the tropics • Sweet pepper • Tensiometers • Soil moisture profile • Root development • Solute distribution

² Former graduate student, now research soil physicist at Land Resource Res. Inst., Ottawa, Canada; professor of soil science and former professor and soil scientist, Univ. of Puerto Rico, now consultant, Cornell Univ.

Received for publication August 7, 1978.