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Soil Nitrate and Water Dynamics in Sesbania Fallows, Weed Fallows, and Maize

Univ. of Technology, Dep. of Agriculture, Private Mail Bag, Lae, Papua New Guinea

B.H. Janssen

Dep. of Soil Science and Plant Nutrition, Wageningen Agricultural Univ., P.O. Box 8005, 6700 EC Wageningen, the Netherlands

R. J. Buresh^* and Bashir Jama

International Centre for Research in Agroforestry (ICRAF), P.O. Box 30677, Nairobi, Kenya

*Corresponding author (r.buresh{at}cgnet.com).

ABSTRACT

We hypothesized that the integration of trees into agricultural land-use systems can reduce NO₃ leaching and increase subsoil N utilization. A field study was conducted on a Kandiudalfic Eutrudox (Ochinga site) and a Kandic Paleustalf (Muange site) in the subhumid highlands of Kenya to measure changes in soil NO₃ and water to 200-cm depth for one rainy season in four land-use systems (LUS): (i) planted tree fallow using Sesbania sesban (L.) Merr., (ii) unfertilized maize (Zea mays L.), (iii) weed fallow, and (iv) bare fallow. Subsoil (50-200 cm) NO₃-N at the start of the season ranged from 58 to 87 kg ha^-1 for the four LUS and two sites. In maize, subsoil NO₃-N differed by <5 kg ha^-1 between planting and harvest at both sites. In sesbania, subsoil NO₃-N decreased by 22 kg ha^-1 at both sites, whereas in weed fallow subsoil NO₃-N decreased by 26 and 38 kg ha^-1 at Ochinga and Muange, respectively. At both sites, subsoil water contents at the start of the season were similar in the four LUS; but at the end of the season, soil water at 100 to 200 cm was significantly lower for sesbania than for maize. Adsorption of NO₃ increased with soil depth. Sorbed NO₃ at 100 to 200 cm was about 60% in the Kandiudalfic Eutrudox and about 15% in the Kandic Paleustalf. Rotation of maize with either a sesbania fallow or a weed fallow can result in more effective subsoil NO₃ and water utilization than maize monoculture.

Received for publication March 1, 1995.

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