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Legume Contributions to Yields and Compositions of Desmodium Spp.-Pangolagrass Mixtures¹

A field experiment on a Humic Latosol at 640-m elevation compared pure pangolagrass (Digitaria decumbens) and mixtures of (a) pangolagrass plus uninoculated Desmodium canum, (b) same but inoculated, (c) pangolagrass plus D. intortum in 90 cm rows, and (d) same as (c) but D. intortum in 45 cm rows. All treatments were tested under limed and unlimed conditions. Dry matter yields over a 2-year period averaged: pure pangolagrass 3,780, (a) 6,840, (b) 7,510, (c) 10,810, and (d) 11,960 kg ha^-1 yr^-1. Percentage legume was low in (a) and (b), and over 50% in (c) and (d). Percentage crude protein was also highest in (c) and (d). The CP yields of the mixtures were approximately equivalent to pure pangolagrass fertilized with N (as (NH₄)₂SO₄) at the following rates: (a) 210, (b) 240, (c) 440, and (d) 525 kg N ha^-1 yr^-1.

Apparent N-fixation in (b) was 97 kg ha^-1 yr^-1, and inoculation of D. canum [(b) — (a)] gave a nonsignificant benefit of approximately 17 kg N ha^-1 yr-1. D. intortum fixed approximately 213 kg ha^-1 yr^-1 in (c) and 264 kg in (d). The total amount of fixed N transferred to the grass was higher for D. intortum, but a higher percentage of the fixed N was transferred from D. canum.

There were wide seasonal variations in dry matter yields and percentage crude protein, but the ranking of the treatments was quite consistent throughout the 2-year period for both of these characteristics. D. canum growth was reduced at average night temperatures below 16 C while D. intortum was affected little until average night temperatures fell below 15 C.

There was no benefit for liming in any of the treatments. Yields of D. intortum were depressed when exchangeable potassium was approximately 0.1 meq/100 g of soil.

Key Words: N-fixation • N-transfer • average night temperature • potassium requirement

² Assistant Agronomist and Associate Soil Scientist, Hawaii Agricultural Experiment Station, University of Hawaii.

Received for publication February 19, 1969.