INTRODUCTION

In Kona, Hawaii, coffee is dormant from December to February. Water is critical for spring vegetative growth, on which next year's flowers are produced. Water stress reduces extension growth, node number, and leaf area of coffee, and irrigation increases internode extension and node production.

The objective of this study was to determine the effect of the amount and frequency of irrigation on vegetative growth on coffee

PROCEDURE

Seeds of Coffea arabica 'Typica' were planted in a 1 vermiculite : 1 perlite medium (by volume) in flats in a saranhouse (32% shade). Seedlings were transplanted to 15-cm pots in a 1 soil : 1 peatmoss : 1 vermiculite : 1 perlite medium (by volume) to which was added 6.7 kg Osmocote 16N-7.1P-13.3K per m³ of medium. Plants were grown in a saranhouse, where they attained a height of 40 to 50 cm before the start of the experiment.

In the first experiment, a randomized complete block design with five blocks and five treatments, consisting of 10, 25, 50, 100, or 200 ml of water/day/plant was used. Plant height was measured weekly for 4 weeks. In the second experiment, a randomized complete block design with five blocks and four treatments was used. The watering treatments were: 700 ml once a week, 350 ml twice a week, 175 ml four times a week, or 100 ml daily (total 700 ml/plant/week).

Stem diameter midway on the plant and plant height were measured weekly for four weeks. After four weeks, leaf disks were cut from each of two opposite leaves located midway on the plant. The fresh weight, saturated weight, and dry weight of the leaf disks were determined. The leaf area of each plant was determined using a LI-COR LI-3100 Area Meter. Abscised leaves were not included in the leaf area measurements. Leaves and stems were dried at 60° for four days, and dry weights were taken.

RESULTS AND DISCUSSION

The 10- and 25-ml treatments resulted in negative height differences after three and four weeks due to wilting and necrosis of the terminal shoot. The 50-ml treatment did not increase height after two weeks, but with the 100- and 200-ml treatments plant height increased throughout the four-week period.

Height differences after four weeks were not significantly different amount treatments (Table 1). Leaf disk fresh weight, dry weight, water content, and relative water content were not significantly different.

The once-a-week watering treatment decreased leaf area significantly. Although the coffee leaf disk water content and relative water content for the once-a-week watering treatment were not significantly different compared to the other treatments, the plants still may have been under sufficient water stress to result in leaf abscission. Leaf dry weight for the once-a-week watering treatment was significantly reduced.

Table 1. Effect of frequency of watering on growth of potted coffee plants after four weeks. A total of 700 ml of water was applied per plant per week.