Effects of water table depth on nitrogen accumulation and pod yield of peanut

ABSTRACT:

Peanut is an important leguminous row crop in the Coastal Plain of the southeastern US. Its growth and yield are dependent upon dinitrogen fixation, a biological process that is adversely affected by water deficits or excesses. Drought and excessive rainfall in the same growing season present special problems for crop production in this region. A two-year field experiment was conducted to assess the effects of controlled drainage/subirrigation on peanut nitrogen accumulation and pod yield. The experiment was located on a lateral of the main channel in a PL-566 drainage district that was equipped with a water table management structure. Water table depths (WTD) were obtained from natural variations in the surface elevation; four, nonrandomized blocks contained WTD of 0.61, 0.76 0.91, 1.07, and 1.22 m (2, 2.5, 3, 3.5, and 4 ft). Plots consisted of eight 15 m (49 ft) rows on 0.91 m (3 ft) spacings. Peanuts (Arachis hypogaea L., CV Florigiant) were planted during the second week in May. Shoots and roots were sampled from 0.30 m (1 ft) of row; shoots were analyzed for total nitrogen, and roots were assayed for dinitrogen fixation by acetylene reduction. Yields were taken from 30 m (98 ft) of row. Rainfall accumulations were 406 and 634 mm (16 and 25 in) in the first and second year, respectively. Pod yields ranged from 3.5 to 5.5 Mg ha⁻¹ (1.6 and 2.5t ac⁻¹) and were > 4.0 Mg ha⁻¹ (1.8t ac⁻¹), if WTD were < 0.91 m. dry matter accumulation, acetylene reduction, and peanut pod yield were negatively correlated with WTD in the first year (R² values > 0.37), but there were no meaningful correlations between plant characteristics and WTD in the second season because sufficient rainfall had eliminated peanut water stress. However, differences in the partitioning of dy matter between the peanut vegetation and fruit produced differences in estimated net soil nitrogen accumulation. When dinitrogen fixation was assumed to provide 45 percent of the total N, estimated net N accumulations were negative and poorly correlated to depth (R² of 0.02) in the drier year. In the wetter year, estimates of net soil nitrogen accumulation ranged from 64 to 4 kg ha¹ (57 to 3.6 lb ac⁻¹), and the R² and slop of the linear regression of net N and WID were 0.40 and -1.05, respectively. Thus, water table management and controlled drainage/subimgation may offer a method that will reduce excess nitrogen and the associated nitrate pollution potential as well as stabilize peanut yield.