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The First Large Absorption Survey in H i (FLASH): I. Science goals and survey design
- James R. Allison, E. M. Sadler, A. D. Amaral, T. An, S. J. Curran, J. Darling, A. C. Edge, S. L. Ellison, K. L. Emig, B. M. Gaensler, L. Garratt-Smithson, M. Glowacki, K. Grasha, B. S. Koribalski, C. del P. Lagos, P. Lah, E. K. Mahony, S. A. Mao, R. Morganti, V. A. Moss, M. Pettini, K. A. Pimbblet, C. Power, P. Salas, L. Staveley-Smith, M. T. Whiting, O. I. Wong, H. Yoon, Z. Zheng, M. A. Zwaan
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- Journal:
- Publications of the Astronomical Society of Australia / Volume 39 / 2022
- Published online by Cambridge University Press:
- 21 March 2022, e010
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We describe the scientific goals and survey design of the First Large Absorption Survey in H i (FLASH), a wide field survey for 21-cm line absorption in neutral atomic hydrogen (H i) at intermediate cosmological redshifts. FLASH will be carried out with the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope and is planned to cover the sky south of $\delta \approx +40\,\deg$ at frequencies between 711.5 and 999.5 MHz. At redshifts between $z = 0.4$ and $1.0$ (look-back times of 4 – 8 Gyr), the H i content of the Universe has been poorly explored due to the difficulty of carrying out radio surveys for faint 21-cm line emission and, at ultra-violet wavelengths, space-borne searches for Damped Lyman- $\alpha$ absorption in quasar spectra. The ASKAP wide field of view and large spectral bandwidth, in combination with a radio-quiet site, will enable a search for absorption lines in the radio spectra of bright continuum sources over 80% of the sky. This survey is expected to detect at least several hundred intervening 21-cm absorbers and will produce an H i-absorption-selected catalogue of galaxies rich in cool, star-forming gas, some of which may be concealed from optical surveys. Likewise, at least several hundred associated 21-cm absorbers are expected to be detected within the host galaxies of radio sources at $0.4 < z < 1.0$ , providing valuable kinematical information for models of gas accretion and jet-driven feedback in radio-loud active galactic nuclei. FLASH will also detect OH 18-cm absorbers in diffuse molecular gas, megamaser OH emission, radio recombination lines, and stacked H i emission.
DURATION OF SESBANIA FALLOW EFFECT FOR NITROGEN REQUIREMENT OF MAIZE IN PLANTED FALLOW–MAIZE ROTATION IN WESTERN KENYA
- M. R. Rao, M. N. Mathuva, E. Gacheru, S. Radersma, P. C. Smithson, B. Jama
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- Journal:
- Experimental Agriculture / Volume 38 / Issue 2 / April 2002
- Published online by Cambridge University Press:
- 28 March 2002, pp. 223-236
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The duration of the residual effect of sesbania (Sesbania sesban) fallow on subsequent crops will determine the interval at which sesbania must be grown to replenish N in a planted fallow–crop rotation cycle. An experiment was conducted from 1995 to 1998 (seven cropping seasons) on two farms in western Kenya, an area subject to a bimodal annual rainfall pattern. The aim was to compare the effect of a single-season sesbania fallow with continuous annual cropping with and without phosphorus fertilizer, on a P-deficient soil. Phosphorus was applied at a rate of 500 kg ha−1 in a single application to meet the phosphorus needs of subsequent crops for the next five to ten years. Sesbania was established simultaneously with maize by direct seeding in the first rainy season of 1995 and allowed to grow as a pure fallow through the second rainy season. Following the harvest of this fallow crop, sole maize in the first post-fallow season and maize-bean intercrops in the subsequent four seasons were grown with and without nitrogen at a rate of 100 kg ha−1. Added phosphorus on average increased maize yields by 3.7 times over the control, indicating that phosphorus fertilizer is essential for good yields. The amount of phosphorus recycled by sesbania fallow was inadequate to meet the crop needs in P-deficient soils. While continuously cropped maize in the presence of phosphorus responded to nitrogen in all seasons, the crop following sesbania responded only from the third season. In the first post-fallow season, sesbania increased maize grain yields over continuous maize by 1.4 t ha−1 with phosphorus fertilizer and by 1.3 t ha−1 without phosphorus fertilizer. The residual effect of sesbania with phosphorus fertilizer lasted for two seasons, while without phosphorus it lasted for only one. In these Kenyan highlands, farmers who can afford fertilizer should buy phosphorus fertilizer and rely for nitrogen on planted fallow with species such as sesbania grown for one season every two years. For farmers who cannot afford fertilizer, one-season fallow every year may be more attractive because of labour savings and the firewood produced by sesbania.