Grain and Forage Legume Yields, With or Without Intercropping and the Effect of Leucaena Green Leaf Manuring on Nitrogen Economy of Corn

Field: Agricultural and Biological Sciences (Life Sciences)

Field experiments involving growing of two grain legumes and two forage legumes with or without corn were conducted during five consecutive seasons in a very fine, kaolinitic, isohyperthennic, Vertie Haplustoll soil in Hawaii to evaluate the yield potentiality and N economy of these Cropping Systems. Grain legumes evaluated were mungbeans (Vigna radiata) and soybeans (Glycine~). Corn grain yields increased in intercrops as compared to the grain yields in control plots of corn (no N application). The increases in intercropped corn grain yields over grain yields in control plots were 158, 163, and 163% in season 1, and 181, 146, and 118% in season 3 in corn/determinate mungbeans, corn/indeterminate mungbeans, and corn/soybean intercrops, respectively. Grain yields of mungbeans and soybeans were slightly depressed in intercroppings as compared to their monocroppings. Harvest indices and plant heights of intercropped corn and legume crops were not significantly different than those of their monocrops. Total biomass produced by corn/grain legume intercropped plots (6.11 to 10.88 Mg ha-1) were much higher than the biomass produced by control plots (3.08 to 4.33 Mg ha-1) of corn. Total grain produced by corn/grain legume intercroppings (1.58 to 3.45 Mg ha-1) were 4 to 6 times higher than the grain produced by control plots of corn (0.39 to 0.55 Mg ha-1). LAI increased in corn/legume intercrops as compared to their monocrops. LER values in these intercropping systems were in the ranges of 1.9 to 2.2 in season 1 and 1.6 to 1.9 in season 3. The grain yields and the plant heights of corn following grain legume plots in season 2 and season 4 were comparable with those of corn monocrops at 33 to 67 kg ha-1 levels of N application. Nitrogen contributions from grain legumes to associated corn crop were none in season 1 and 10 to 25 kg N ha-1 in season 3. N contributions from legumes to the following corn, however, were 40 to 58 kg N ha-1 in season 2 and 31 to 75 kg ha-1 in season 4. The residual N contribution to the following corn was the highest by indeterminate mungbeans (58.0 to 75.0 kg N ha-1) followed by soybeans (40.0 to 62.5 kg N ha-1) and determinate mungbeans (35.0 to 47.0 kg N ha-1). Nitrogen fixation by mungbeans and soybeans were not depressed in intercroppings as compared to their monocroppings, except in soybeans in season 1 where soybeans were shaded by corn. Forage legumes evaluated were leucaena (Leucaena leucocephala) and desmodium (Desmodium intortum), Grain yields of corn intercropped with leucaena were slightly higher than in control plots in all seasons except season 2, where corn was shaded by leuceana. Grain yields of corn intercropped with leucaena were 128, 60, 122, and 102% of control plots of corn in season 1 to 4, respectively. Grain yields of corn intercropped with desmodium were slightly lowerthan the control plots of corn in all seasons except season 4. Grain yields of corn intercropped with desmodium were 72, 71, 91, and 118% of control plots of corn in season 1 to 4, respectively. In general, corn did better with leucaena than with desmodium. However, corn seemed to perform better with leucaena during summer and better with desmodium during winter periods. Seasonal forage yields of leucaena and desmodium were not different in intercrops than in their monocrops. Total biomass produced by corn/forage legume intercropped plots (4.5 to 17.0 Mg ha-1) were much higher than the biomass produced by control plots (3.08 to 4.33 Mg ha-1) of corn. LAI was higher in intercropping than in the control plot of corn. Total LER values in corn/leucaena and corn/desmodium intercrops were in the ranges of 1.40 to 2.10 and 1.60 to 1.81, respectively. Nitrogen produced by leucaena was from 630 to 653 kg ha-1 yr-1 and by desmodiurn was from 508 to 608 kg ha-1 yr-1. Total N yields obtained from corn/leucaena intercroppings were 7 to 21 times and from corn/desmodium intercroppings were 7 to 14 times as much as the N yields obtained from the control plots of corn. N contributions from forage legumes to associated corn were none in season 1 and season 2, however, there was some N contribution from legume to associated corn in season 3 and season 4 (19 to 30 kg N ha-1 from leucaena and 9 to 17 kg N ha-1 for desmodium). Corn following forage legumes in season 5 received residual N of 21 to 31 kg ha-1 from leucaena plots and 23 to 30 kg ha-1 from desmodium plots. In another field experiment, leucaena forage was incorporated into soil as green manure for corn and the residual effects were evaluated in the second season. Corn grain yields obtained from the leucaena green manuring at the rates of 47, 94, and 141 kg N ha-1 were equivalent to corn grain yields obtained from the urea-N rates of 18, 35, and 58 kg N ha-1, respectively. The efficiency of leucaena green manure to increase corn grain yield as compared to urea-N applications were 37 to 41%. The amount of residual N from leucaena green manure to the following crop of corn were equivalent to urea-N application rate of 13 to 30 kg N ha-1. Recoveries of N from urea-N were 39.4 to 47.0% and from leucaena-N were 26.3 to 30.5% in season 1. Recoveries of residual leucaena-N in season 2 were 5.0 to 7.1%. The total N recovered from the applied leucaena green manure were 31.7 to 37.6% by the two crops of corn. A pot experiment was conducted where 15N-tagged mungbean plant materials, shoot, root, and shoot+ root, were applied to a wheat crop and a second crop of wheat was grown to evaluate the residual 15N remaining. Total dry matter yields and total N uptake by the first crop of wheat increased with increasing rates of mungbean-N. Total dry matter and total N yields by wheat crop 1 obtained from the 100 kg N ha-1 rate of all sources of mungbean-N were comparable with those from 33 kg ha-l rate of urea-N. Except the higher rates of mungbean-N applied (at and above 100 kg N ha-1), the residual effects from all other mungbean-N treatments were not different than the control plot. In both the wheat crops, straw overyielded the grain at all levels and from all sources of N applied. In contrast, N uptake by grain was always higher than that by straw of wheat. Wheat N derived from mungbean-N increased with increasing rates of mungbean-N applied and were higher (10.9 to 70.4%) by the first crop of wheat and lower (5.4 to 43.5%) by the second crop of wheat. Most of the mungbean-N applied were recovered by the first crop of wheat (11.1 to 33.9%) and only less than 6% of the N was recovered by the second crop of wheat. Recoveries of N were higher from shoot than from root treatments. Of the two methods used, the difference method overestimated the N recovery over the isotopic method.