Estimation of Nitrogen Fixation by the Natural15N-abundance Technique and Nitrogen Uptake by Pigeonpea Genotypes of Different Maturity Groups grown in an Inceptisol

Over 2 tons of dry matter per acre were obtained from pure seedings of timothy and of brome in the seeding year with an application of 100 pounds of nitrogen per acre. Nitrogen at 200 and 400 pounds per acre produced no further significant yield increase. In the second year, yields were significantly increased by each increment of nitrogen applied in the seeding year up to and including 400 pounds per acre with brome and 200 pounds per acre with timothy. Nitrogen content of grasses increased with each increment of nitrogen in the seeding year but this effect was not consistent in the second year. Over the 2-year period grasses recovered approximately 65 per cent of the applied nitrogen at the 100- and 200-pound levels and about 40 per cent at the 400-pound level.Red clover and alfalfa seeded in mixture with timothy and with brome were about equal in yield to grass alone plus 100 pounds of nitrogen in the seeding year and were much superior in the second year. Application of 100 pounds of nitrogen to grass-legume mixtures increased both yield and nitrogen content in the first cutting. In subsequent cuttings, total yield and legume fraction of the yield were often depressed by nitrogen treatment; exceptions were noted where legume stands were weak.Apparent nitrogen fixation by the legumes was consistently reduced by nitrogen treatment. Vigorous legume stands had an apparent nitrogen fixation of 60 pounds per acre in the seeding year and up to 200 pounds in the second year.

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Response of Azolla Caroliniana and Rice to Phosphorus Enrichment of the Azolla Inoculum and Phosphorus Fertilization During Intercropping

Experimental Agriculture ◽

10.1017/s0014479700024972 ◽

1995 ◽

Vol 31 (1) ◽

pp. 21-26 ◽

Cited By ~ 6

Author(s):

D. P. Singh ◽

P. K. Singh

Keyword(s):

Nitrogen Fixation ◽

Nitrogen Uptake ◽

Phosphorus Content ◽

Dry Weight ◽

Phosphorus Fertilization ◽

Higher Plant ◽

Phosphorus Enrichment ◽

Straw Yield ◽

Azolla Caroliniana ◽

Nitrogen Yield

SummaryThe effects of phosphorus enrichment of Azolla inoculum and phosphorus fertilization during intercropping on the growth, nitrogen fixation and phosphorus content of Azolla caroliniana and the grain yield, straw yield and nitrogen uptake of rice were studied for four consecutive seasons. The phosphorus-enriched Azolla maintained a higher plant phosphorus content and produced a greater biomass and nitrogen yield than the unenriched Azolla. Application of phosphorus during intercropping significantly increased the dry weight, nitrogen yield and phosphorus content of both unenriched and phosphorus-enriched Azolla. The differences between the enriched and unenriched Azolla declined as increasing levels of phosphorus were applied during intercropping. The grain and straw yields and nitrogen uptake of rice were increased both by phosphorus-enrichment of Azolla inoculum and by phosphorus fertilization during intercropping.La gestión de fósforos para la siembra simultánea del Azolla y el arroz

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