Management of Leucaena leucocephala (Lam.) de Wit for Maximwn Yield and Nitrogen Contribution to Intercropped Com

Abstract

The performance of the Hawaiian type (K341) of L. leucocephala (Lam.) de Wit was compared with that of a Salvador type (KB) in field experiments at North Kohala, Hawaii (130 m elevation, Typic Ustropepts). In a second experiment, leucaena (KB) was intercropped with corn (H610) to study their relative yields and the nitrogen contribution of leucaena to intercropped corn. Spacing, cutting regimes and climatic factors significantly affected the morphological development and yield of both varieties. Growth rate and yields were higher during periods of ·high solar radiation and night temperature values. The early flowering habits of K341 coupled with more lateral branching resulted in a shrubby type of growth; while the apically dominant KB assumed a single-shoot type of growth. The flowering of K341 was enhanced at the lower planting densities. The faster rate of growth of KB contributed to its more rapid increased interception of sunlight than K341 as both approached the cutting stages. At harvest, the light interception was about identical at 96 percent. The total annual dry matter yields were 17.8 t/ha for K341 and 15.2 t/ha for KB. These yields consisted of 12.0 tons of forage fraction (leaves+ succulent stems) for K341 (513 kg N/ha/yr) and 9.9 tons of forage fraction for KB (429 kg N/ha/yr). The remainder was hard stem. Yields decreased with frequent cutting and wider plant spacing. However, the percent forage fraction was higher -under more frequent cutting and wider plant spacing. Therefore, dense planting (15 cm x 50 cm) and cutting at approximately 1 m height at harvest were desirable management practices considering the forage yield, the percentage forage fraction, and the average cutting frequency (3-month interval). Nitrogen and mimosine contents of the forage fraction and stem on a dry weight basis were similar in all treatments. Forage fraction contained 4.30 percent nitrogen and 6.6 percent mimosine. The stems contained 1.5% N and 0.92% mimosine. Crude protein in the forage fraction and stem was comprised of about 24 percent and 10 percent mimosine, respectively. Based on forage fraction, K341 produced nearly 600 kg N/ha/yr while K8 produced about 500 kg N/ha/yr. The differences in the N yields among treatments were due to differences in dry matter yields. Unlike tillering grasses, leucaena was not able to compensate for the wider spacing by producing more stems. Therefore, optimum density at planting was critical in leucaena for maximum yield production. Stem diameter was similar for both varieties at harvest (8.2 mm overall average). Delayed cutting and wider plant spacing resulted in larger stem diameters. Forage production of leucaena was about 1/2 - 2/3 that of alfalfa. Weed control was more of a problem with leucaena than with alfalfa. However, leucaena production involved easier agronomic management than alfalfa because of less frequent harvests, greater harvest flexibility, freedom from disease infestations and longevity of stand. When leucaena was intercropped with corn, it made excellent growth, with yields on a unit area basis comparable to the monocropping experiment. The amount of leucaena plant material produced and added to the corn increased with delayed cutting, with double rows of leucaena and to a small degree, with decreased corn plant density. Percent nitrogen in the leucaena plant material decreased with delayed cutting because of the increased proportion of stem compared to forage fraction. The amount of leucaena-N applied to each corn crop varied from about 60 to 180 kg/ha. In the first corn crop, the yields of corn grain and stover were not influenced by the application of either urea or leucaena forage. This was due to residual soil nitrogen from a previous sorghtllll experiment and to the limited quantities of leucaena added to the soil. The grain yields of corn intercropped with a single row of leucaena cut at seedling (3.40 t/ha) or tasseling (3.56 t/ha) stage were comparable to the grain yields of the check plot (3.45 t/ha). The nitrogen content of the ear leaf samples of intercropped corn ranged from 2.3 - 2.7% with no differences due to treatments. This was similar to the ear leaf samples from the check plots which ranged from 2.42 - 2.9% nitrogen. In the second crop of corn, there was a significant response to both urea and leucaena forage application. Yields of corn seedlings, grain and stover in the corn-leucaena intercrop were generally higher than in the check. Corn seedlings yielded from 2.70 4.36 g/plant with leucaena-N compared to 1.48 - 1.86 g/plant in the check treatment. 'The grain yields of corn intercropped with leucaena averaged 2.39 t/ha - ' r' 23 percent higher than the check. Grain yields were higher when leucaena was cut at the early stage of corn than at later stages of growth because in the former, the nitrogen could not be effectively utilized by the corn. Yields of corn grain and stover from corn intercropped with double rows of leucaena were lower than corn from single leucaena row treatments on a field area basis, but double-leucaena-row treatments yielded higher on a corn area basis. Higher grain and stover production were obtained with close corn spacing (15 cm) than wide spacing (30 or 45 cm). The effects of various treatments on the Ncontents of the plant samples were similar to their effects on grain yields. Nitrogen content of the seedlings, leaf and whole plant samples increased with increasing rates of urea and leucaena forage application. In the urea-N treatments, plant spacing had a limited influence on the N content of the seedlings; a greater influence was observed at the later stage of plant growth. In the corn-leucaena intercrop, the nitrogen content of the corn plant tissue increased consistently under lower planting density. The nitrogen contribution of leucaena forage were estimated on the basis of: (1) the level of N nutrition in the corn plant tissue samples, (2) the weight of corn seedlings, and (3) grain yields. The equivalent urea-N levels in the intercropped corn were as follows: corn plant tissue samples, 9 - 28 kg N/ha; weight of seedlings, 32 - 58 kg N/ha; and grain yield, 0 - 12 kg N/ha. The efficiency of leucaena in supplying nitrogen to corn was about 38 percent of that of urea, based on the grain yield. Corn spacing accounted for most of the variation in yield in the leucaena treatments (r2 = 82%), but there was an improvement in the coefficient of determination when leucaena-N data were added to the spacing data (R2 = 88%). The total fresh forage production in corn-leucaena intercrop and in corn alone fertilized with 75 kg N/ha from urea was comparable, at 24 t/ha. This yield was twice the fresh forage yield of corn under zero nitrogen plot. Percent crude protein and crude protein yield of the forage were significantly higher in the corn-leucaena mixed forage compared to corn forage without leucaena. Percent crude protein of the cornleucaena ranged from 15.9 to 21.98% while under zero nitrogen and 75 kg N/ha treatments, the maximum percent crude protein concentrations were 9.90% and 12.07%, respectively. Crude protein yield in the cornleucaena treatment was 1.44 t/ha, twice the yield under 75 kg N/ha and three times the yield under zero nitrogen plot. Leucaena contributed significantly to reducing the nitrogen requirement of the intercropped corn. In addition to nitrogen, leucaena forage undoubtedly contributed other nutrients to corn. Forage nutrient values increased considerably when leucaena was mixed with the corn.