A simple, low-cost technique for in situ measurement of leaf P concentration in field-grown rice

Simple tools for diagnosing crop nutritional status are in great demand by agricultural extension staff, particularly in low-fertility environments. We developed the first practical method for in situ diagnosis of phosphorus (P) nutrition in field-grown cereal crops by using a handheld colorimeter. The concentration of P in extracts from fresh leaves of lowland rice grown under various P availabilities was closely correlated with that of oven-dried leaves measured with the standard molybdenum-blue method in the laboratory, over a range of values from 0.319 to 1.420 mg P g ⁻¹ DW (r = 0.885 ^** , n = 14). It takes only 3–5 min to estimate the P concentration of plant samples using the new technique. Although not as accurate as the laboratory method, the new method can easily detect P deficiency of rice in the field (and possibly other cereal crops) without requiring costly, off-site equipment. Thus, extension staff and agronomists can easily adopt this technique.