THE PIGEON PEA! CULTURE IN HAWAII. 21 
tices have longer or better stood the test of time than green manuring 
and the systematic rotation of crops. In Hawaii no other crop is 
known that will lend itself more readily to a large variety of condi- 
tions than the pigeon pea. On account of its ready adaptability to 
soil and climate, its drought-resistant properties, deep-rooting habit, 
heavy production of rich nitrogenous vegetation, perennial nature, 
and thrift under neglect, the pigeon pea is peculiarly well suited to 
follow the pineapple and sugar-cane crops after these have spent 
themselves. Resting the land is said to restore fertility, but a more 
effective means of restoring fertility is to change the use of the land 
by practice of rotation of crops. The cropping cycle of sugar cane, 
pineapples, and pigeon peas in terms of time is quite similar. On 
an average, the two great staple crops of Hawaii have a cropping 
cycle consisting of a plant crop and two ratoon crops, covering 
approximately five years. This is likewise true of pigeon peas. 
Not only is it good theory but actual experimental practice has 
demonstrated that worn-out pineapple lands may be restored to 
their original, or to improved, fertility by allowing a crop of 
pigeon peas to occupy the land for a period equal to the time such 
lands were cropped to pineapples, the pigeon peas then being turned 
under as green manure. This was demonstrated in a pineapple field 
two years old which yielded 20 tons of A No. 1 fruit during the 
1919 season. (.PL V, fig. 2.) Pigeon peas were grown on this field 
for three years and the entire crop was then turned under. The 
tonnage of vegetable matter, including the roots, woody trunks, and 
foliage, was approximately 50 tons per acre. In addition to this 
final green-manuring crop, much leafy matter was shed on the 
ground beneath the plants, so that in places a leaf mold an inch or 
two thick had accumulated. This leaf mold was difficult to estimate, 
but in three years it must have yielded fully 5 tons per acre of the 
richest kind of organic matter. Just before the pigeon peas were 
planted, the pineapple crop on the same land collapsed at the end 
of the first harvest. While the present crop (second, or first ratoon, 
crop) of pineapples succeeding the pigeon peas is only just now 
maturing, there is every indication that the crop will carry safely 
into the second ratoon crop. If this proves to be the case, then there 
has been evolved an extremely simple cropping system, the rotation 
of pineapples with pigeon peas, an 8 to 10-year rotation, allowing 
4 or 5 years to each crop. In this rotation each of the " crops " 
is a dominating factor for a permanent and profitable agriculture 
and therefore good farming. It is believed that what is apparently 
proving so beneficial to the pineapple crop will prove equally bene- 
ficial to the sugar-cane crop. Sugar planters will doubtless welcome 
a dependable cover crop that is not only suitable for green manur- 
