The use of SPAD-502 chlorophyll meter for dynamically optimizing the nitrogen supply in potato crop: First results

An experiment was conducted on potato cv. 'Primura' to test the usefulness of SPAD threshold values in decision making for supplemental nitrogen supply in 2000. A non-fertilized control was compared with nine fertilized treatments receiving 30 kg ha-1 of N (urea 46% N) at crop emergence plus supplementary nitrogen which was applied as follows: i) five treatments provided increasing rates of N (30, 90, 150, 210 o 270 kg N ha-1, urea 46% N) distributed 18 days after emergence, (conventional fertilization, CF); ii) four treatments provided supplemental nitrogen application (urea, 46% N) when the SPAD values fell below the critical value of 39 SPAD (dynamic fertilization, DF). This critical level corresponds to 10% deviation from threshold value of 45-45 SPAD calculated in a previous work. Each time, increasing rates of N were distributed to the soil (30, 60 or 90 kg N ha-1 - 30 DF, 60 DF and 90 DF), or 9.2 kg N ha-1 was applied via foliar spray (foliar DF). In these treatments, the number of N applications and the total amount of N distributed to the crop were 4, 3, 3 and 5, and 120, 150, 210 and 76 kg N ha-1, respectively. Yield response to CF treatments were optimum with 180 kg N ha-1 (180 CF = 30+150 kg N ha-1). Yield of DF treatments did not differ from 180 CF. These results, particularly 30 DF and foliar DF treatments had amount of N distributed reduced by 30% and 60% as compared to 180 CF.