Abstract
Small analytical systems enabling rapid on-farm analysis may be useful for monitoring crop and soil nutrient status. Two commercially available, rapid analysis systems were evaluated for analysis of (NO3-) in aqueous standard solutions (AS), and in soil solution (SS), plant sap (PS) and fertigation nutrient solutions (NS) obtained from tomato crops. The systems were the Merck RQFlex reflectometer and the Hanna Instruments C115 Grow Master colorimeter. (NO3-) in AS covered the analytical range of each instrument, being 0.3-3.2 and 0.3-16.1 mmol/L, respectively, for the reflectometer and colorimeter. (NO3-) were 5-14 mmol/L for SS, 2.3-33 mmol/L for NS, and 63-158 mmol/L for PS. Accuracy was evaluated using linear regression against (1) known concentration for AS, and (2) laboratory analysis for SS, PS and NS. For the reflectometer with AS, SS and PS, the linear regression had slopes of 1 +/ - 0.08 and intercepts of /= 0.94. The reflectometer was generally accurate for all media examined; it was rapid (1 min per analysis) and simple to use. The colorimeter was generally similarly accurate; however, it was slower, required reagent preparation and was subject to colour interferences. This work demonstrated that the reflectometer can provide rapid and accurate on-farm measurement of (NO3-) in SS, PS and NS.
Highlights
Intensive vegetable production systems are generally characterised by high inputs of nitrogen (N) and low recovery of applied N by vegetable crops (Pratt, 1984; Balusubramanian et al, 2004)
Two portable rapid analytical systems were evaluated for their accuracy in the analysis of NO3- in aqueous standard solutions, soil solution obtained with ceramic cup suction samplers, plant sap and fertigation nutrient solutions
There was a linear response across the concentration range of 0.3 to 3.2 mmol L-1 (Fig. 1a, Table 2), this range is very similar to the stated operating range of 0.1 to 3.6 mmol L-1
Summary
Intensive vegetable production systems are generally characterised by high inputs of nitrogen (N) and low recovery of applied N by vegetable crops (Pratt, 1984; Balusubramanian et al, 2004). The combined use of (i) drip irrigation, (ii) fertigation systems and (iii) programmable controllers is increasing in intensive vegetable production systems Such combined systems are commonly used in substrate-based production (Adams, 2002), and are being increasingly adopted in soil-based vegetable production such as in the greenhouse-based vegetable production system of south-eastern Spain (Carreño and Magan, 1999; Pérez-Parra and Céspedes, 2001). These combined systems enable frequent application of precise volumes of water with specified concentrations of selected nutrients, providing vegetable growers with the technical capacity to “spoon-feed” nutrients to crops. To take advantage of the technical capacity of combined drip irrigation/fertigation systems for precise N application, the adoption of improved N management practices is required
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