In regions with shallow water tables, ground water may have a positive (water supply) or negative
(waterlogging or salinization) impact on crops. Reciprocally, crops can influence ground water, altering
water table depth and chemical composition. We quantified these reciprocal influences along natural
gradients of groundwater depth in flat sedimentary landscapes of the Inland Pampas occupied by wheat,
soybean, and maize during two growing seasons (2006/2007 and 2007/2008). We correlated crop yield
and groundwater depth maps at the field level and made direct plant, soil and groundwater observations
at the stand level across topographic gradients. Water table level largely accounted for spatial crop yield
variation, explaining 20–75% of their variance. An optimumgroundwater depth range, where crop yields
were highest, was observed for all three crop species analyzed (1.40–2.45 m for maize, 1.20–2.20 m for
soybean, and 0.70–1.65 mfor wheat). The areas within these optimumbands had yields that were 3.7, 3
and 1.8 times larger than those where the water table was below 4 m for wheat, maize, and soybean,
respectively. As groundwater levels become shallower than these depth bands, crop yields declined
sharply ( 0.05 kg m 2 on average for every 10 cm increase in water table level), suggesting negative
effects of waterlogging, root anoxia and/or salinity. Groundwater levels below these depth bands were
associated with gradually declining yields, likely driven by poorer groundwater supply.
Crops influenced groundwater levels through their control of recharge and discharge fluxes. The
presence of active crops prevented recharge events (sharp water table level rises) observed during rainy
periods in fall and spring. Crops consumed ground water generating increasing discharge as the water
table depth decreased. This consumption led to rising soil and groundwater salinization towards
shallower water table positions as the growing season progressed. The electrical conductivity of ground
water for maize at maturity doubled the pre-sowing values ( 2.2 dS m 1 vs. 1.1 dS m 1, p when ground water was above 2-m depth, whereas negligible changes were observed when
groundwater depth exceeded 3.5 m. In flat humid landscapes, such as the Inland Pampas, crops and
shallow ground water may be closely connected and influence each other through different mechanisms,
posing both opportunities and risks for agricultural systems. Understanding these complex interactions
could help raise and stabilize yields and provide keys to regulate the labile hydrology of these plains.

Nosetto, M.D., Jobbágy, E.G., Jackson, R.B., Sznaider, G.A.
Land Use, Biofuels and Rural Development in the La Plata Basin (Latin America)
Utilisation des terres, biocombustibles et développement rural dans l'estuaire du río de la Plata (Amérique latine)
Published date
Friday, January 2, 2009 - 05:00
Open Access
Article Type
Keywords Raw