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Root Zone Water Balances of Three Low-Input Millet Fields in Niger, West Africa

Payne, Dep. of Soil and Crop Sci., Texas A&M Univ., College Station, TX 77843

C. W. Wendt and R. J. Lascano

Texas Agric. Exp. Stn., Rt. 3, Lubbock, TX 79401.

^* Corresponding author.

It is often assumed that pearl millet [Pennisetum americanum (L.) Schum.] production is limited by water supply despite the fact that little published data exist on water balances of low-input millet fields. The objectives of this study were to: (i) quantify components of the field water balance of three sites, each in a different rainfall zone, and (ii) determine whether water supply was the primary limiting constraint to production at each site. The study was conducted on sandy soils in Niger, West Africa, during the 1985 growing season. Fields were near the villages of Chikal, N'Dounga and Kala Paté, which received 223, 344 and 428 mm of total rainfall, respectively. Soils were classified as Ustic Torripsamment at Chikal, Psammentic Paleustalf at N'Dounga, and Alfic Ustipsamment at Kala Paté Water balances were calculated to the depth of maximum root penetration, which was determined at harvest by digging pits. Measurements were made using a field calibrated neutron probe and nonrecording rain gauges. Results indicate that depth of maximum root penetration was not correlated with rainfall received after planting. Seasonal crop water supply was greatest at N'Dounga, where root development was greatest. Drainage below the zone of maximum root penetration was significant at Kala Paté at 43 d after sowing, when cumulative rainfall was only 143 mm, but negligible at the other sites. Drainage could not be separated from evapotranspiration at Kala Paté 67 d after sowing and thereafter. Total evapotranspiration was 272 mm at N'Dounga and 201 mm at Chikal. Cumulative change in water storage in the zone of maximum root penetration was 0 mm at Chikal, 39 mm at N'Dounga, and 46 mm at Kala Paté. Based on the amount of water held above – 1500 kPa in the zone of maximum root penetration and profile water distribution, we conclude that water was the primary limiting constraint only at Chikal in 1985. Water supply did not appear to be the primary limiting constraint at N'Dounga and Kala Paté. Similar conclusions were obtained using the amount of root zone water held above – 100 kPa. The study suggests that water supply may not be assumed a priori to be the primary production constraint to low input millet fields such as those studied here.

Received for publication May 1, 1989.

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