Evaluation of NO3-N Leaching in Commercial Fields of Leafy Vegetables by the Soil Nitrogen Balance Estimation System

Nitrogen (N) is one of the most important element limiting nutrients for plant growth and one of the largest energy-input in agricultural production systems is through N fertilizers. Intensive crop production involves the application of inorganic and organic N fertilizer forms to supplement the soil resource base (Christian and Riche, 1998). Over-fertilization and inappropriate timing of fertilizer application may enrich soil water with nitrate-N (NO3-N) (Christian and Riche, 1998) and result to NO3-N leaching that is economically and environmentally undesirable (Asadi and Clemente, 2003; Luce et al., 2011). Several strategies of managing soil N that may reduce or prevent NO3-N leaching in intensive crop production systems have been proposed and experimented (Horiuchi, 2001; Di and Cameron, 2002; Qiaogang et al., 2008; Zupanc et al., 2011). However, in intensive leafy vegetable production systems, excessive application of N in the form of chemical fertilizers to achieve maximum yield per cultivated area is usually accompanied by NO3-N leaching (Mishima, 2001). NO3 -N leaching below the rooting zone results to point and non-point-source pollution and high cost-benefit ratio of agricultural production are sustainability issues that have been addressed for decades (Kumazawa, 1999; Maeda et al., 2003; Bergström et al., 2005; Schoolman et al., 2011). NO3-N leaching has been evaluated using lysimeters (Ogawa et al., 1979; Kobayashi et al., 1995; Suzuki and Shiga, 2004), porous ceramic cups (Williams and Lord, 1997; Christian and Riche, 1998), ion-exchange-resin cartridges (Predotova et al., 2011) and well calibrated computer models. Traditionally, a technique for monitoring salts in the soil of which NO3-N is not exempted involved core sampling (Patriquin et al., 1993; Eigenberg et al., 2002) or the use of suction probes (Williams and Lord, 1997; Christian and Riche, 1998) and subsequent laboratory analyses. Monitoring solutes in the soil has evolved through destructive and a series of non-destructive methods whose applicability is dependent upon the study objectives. Soil resistivity techniques such as resistance probes, low frequency capacitance probes (Aimrun et al., 2009; Scudiero et al., 2012), time-domain reflectometry (Payero et al., 2006; Krishnapillai and Ranjan, 2009; Persson and Dahlin, 2010), soil water samplers (Higashi et al., 2005), tracers (Shibano and Ohno, 1988) and morphological techniques (Eigenberg et al., 2002) have also been employed to monitor the pathway of solute movement in the soil. Computer models have also been developed for scientific research based on ecosystem management principles