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A B S T R A C TSince there is no information in the green belt of Córdoba, Argentine, about the use of instruments to measure leaf area index (IAF) through light interception in potato crop (Solanum tuberosum L.), a study was developed with the objectives of: i) evaluating the employment and capacity of an optic instrument to determine IAF in a potato crop; ii) verifying IAF and ground cover (%C) using alternative measurements of crop canopy development to estimate intercepted radiation (fAPAR). The measurements were carried out during 2005 (from February 4 to June 1), in a plantation density experiment near Córdoba (31 0 30' S lat, 64 0 08' W long, 402 m.a.s.l.), with three treatments, in pl m -2 : 6.0 ± 0.6 (TDC); 3.9 ± 0.2 (TDB) and 7.9 ± 0.7 (TDA). IAF was estimated by means of an optic instrument (ceptometer) and ground cover (%C) through digital pictures. The IAF values measured with the ceptometer were compared with photogrametric determinations obtaining an acceptable correlation (R 2 = 0.80; P < 0.01). The relationship between IAF and fAPAR remained uniform, in the sense of comparing plantation densities, likewise during different moments of the cycle. Until the crop reaches maximum covering, the relationship between %C and fAPAR was linear, with a highly significant (R 2 = 0.93; P < 0.01) coefficient of adjustment, although it shifts slightly away from a 1:1 relationship. R E S U M E NDebido a que no existen antecedentes en el cinturón verde de Córdoba, Argentina, del uso de aparatos para medir el índice de área foliar (IAF) a través de la intercepción lumínica en el cultivo de papa (Solanum tuberosum L.), se desarrolló un trabajo con estos objetivos: i) evaluar el empleo y capacidad de un instrumento óptico para determinar el IAF; ii) verificar la utilización del IAF y de la cobertura del suelo como mediciones alternativas del desarrollo de la parte aé-rea del cultivo, a fin de estimar la fracción de radiación interceptada (fAPAR). Las mediciones se realizaron durante la campaña de papa semitardía del año 2005 (del 4 de febrero al 1 de junio), en un ensayo de densidad de plantación ubicado próximo a la ciudad de Córdoba (31°30' lat. Sur, 64°08' long. Oeste, 402 m.s.n.m.), que consistió de tres tratamientos, en pl m -2 : 6,0 ± 0,6 (TDC); 3,9 ± 0,2 (TDB) y 7,9 ± 0,7 (TDA). El IAF se midió por medio de un interceptómetro óp-tico y el porcentaje de cobertura del suelo (%C) a partir de fotografías digitales. Los valores de IAF calculados con las mediciones del interceptómetro se contrastaron con determinaciones fotogramétricas, obteniendo una correlación aceptable (R 2 = 0,80; P < 0,01) entre ambos. La relación entre IAF y fAPAR se mantuvo uniforme, tanto en el sentido de comparar las densidades de plantación, como así también durante diferentes momentos del ciclo. Hasta que el cultivo alcanza cobertura máxima, la relación entre %C y fAPAR es lineal, con un coeficiente de ajuste altamente significativo (R 2 = 0,93; P < 0,01), si bien se aparta ligeramente de la relación 1:1.Palabras clave: papa, densidad ...

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AquaCrop model estimates the crop productivity decrease in response to water stress, determining the biomass (B) based on water productivity (WP) and accumulated transpiration (ΣTr); and the yield (Y) is calculated according to B and the harvest index (HI). AquaCrop was evaluated considering different WP values for 2010 late growing season to simulate crop yield of potato (Solanum tuberosum L.) cv. Spunta, in a commercial production field of 9 ha located in the green belt of Cordoba city (31˚30'S, 64˚08'W, 402 m asl), while monitoring in 2009 was used to verify the model. Canopy cover estimation by AquaCrop was adjusted using observed field data obtained from vertical digital photographs acquired at 2.5 m height. WP values of 15.8 and 31.6 (for C 3 and C 4 species, respectively) and two intermediate values 21 and 26.3 g·m −2 were considered to evaluate the model performance. While linear function between observed tuber yields and estimated by AquaCrop had always a correlation coefficient greater than 0.94 (p < 0.001), using WP = 26.3 and WP =31.6 g·m −2 presented overestimation, whereas with 15.8 g·m −2 had an opposite behavior, while WP = 21 g·m −2 was the value that produced the lowest estimation error. In addition, soil moisture from this estimated value of WP was highly correlated with measured water content in different areas of production field. The verification test shows that while the model slightly underestimates canopy cover, biomass was overestimated. After setting the coefficients of canopy cover development, the AquaCrop crop model estimated adequately potato yield for high production values that are less affected by lack of water, but in both years showed a tendency to overestimate the lowest yields, as was observed for other crops. Meanwhile, the dispersion between the observed and estimated yield was higher in the verification test because the sampling this year was more random.

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