Evidence for the Ability of Active‐Optical Sensors to Detect Sulfur Deficiency in Corn

Agronomy Journa l • Volume 108 , I s sue 5 • 2016 I n the United States, soil S levels are decreasing and reports of S defi ciency in crops is increasing in part due to decreased emissions from gaseous S-emitting industries (Schwab, 2008; Franzen, 2015a). Greater S demand from higher crop yields and continued loss of topsoil through wind and water erosion has also contributed to greater frequency and severity of S defi ciency in corn and other crops. Predicting S defi ciency in soils is diffi cult due to the poor relationship between the S soil test and crop response (Pagani and Echeverria, 2011; Franzen, 2015a, 2015b). Presence of S defi ciency in corn can be better determined at physiological maturity with plant tissue analysis (Weil and Mughogho, 2000; Pagani and Echeverria, 2011), but its value to a corn grower at that growth stage is mostly academic, because there is little ability to correct the S defi ciency and increase crop yield. Th ere is minimal literature that documents an interaction between N and S application from low plant available S soils. Some studies have attempted to determine the interaction of N with low S soil levels (Pagani et al., 2009); however, the lack of corn grain yield response with added S indicates that although the researchers tried to fi nd sites where S defi ciency was present, they were unsuccessful. Th e authors of this note have observed a tendency for corn fertilized with high N rates in some experiments to be more yellow in color at V5 and until maturity than lower N and control N treatments in previous years, but there was no attempt to record color diff erences. Malhi and Gill (2007), working on a low S availability Gray Luvisol soil in Saskatchawan documented in a S and N application study in canola (Brassica napus L.), that at the control S rate canola yield declined with N rate at four sites. Only when suffi cient S was applied to overcome the S defi ciency did N rate increase yield. In an Australian N and S rate study (Brennan and Bolland, 2008), canola grain yield decreased at the 0 kg ha–1 S rate when N was applied. Only when S was applied (13–34 kg ha–1) did N rate increase yield. Active-optical sensors have not been utilized in diagnosing S defi ciency to date. Active-optical sensor research has mainly focused on its use to help direct N fertilizer rates in-season for various crops. Th e two main approaches to the use of AO Evidence for the Ability of Active-Optical Sensors to Detect Sulfur Defi ciency in Corn