de θ e Ïs foram feitas metro a metro ao longo de 200 m usando uma sonda de ... variabilidade temporal e espacial, ciclos de umedecimento/secagem, sonda de.
SPATIAL AND TEMPORAL PATTERNS OF SOIL WATER CONTENT AND BULK DENSITY CHANGES IN A FIELD DURING WET AND DRY PERIODS L. C. TIMM1, L.F. PIRES2, R. ROVERATTI2, R.C. J. ARTHUR2, K. REICHARDT2, J.C.M. OLIVEIRA2, O.O.S. BACCHI2 1
Prof. Adjunto, Depto. de Engenharia Rural, FAEM/UFPel, Pelotas – RS, (0XX53) 2757259, e-mail: lctimm@ufpel.edu.br 2 Laboratório de Física do Solo, CENA/USP, Piracicaba - SP Escrito para apresentação no XXXIV Congresso Brasileiro de Engenharia Agrícola 25 a 29 de julho de 2005 - Canoas - RS
ABSTRACT: Soil water content (θ) and bulk density (ρs) greatly influence the important soil and plant processes. Based on this, questions related to the spatial and temporal variability of θ and ρs during different periods of the year and different development phases of the crop become of fundamental interest. This work had as objective the characterization of spatial and temporal patterns of θ and ρs during different climatic periods of year at the soil surface layer when submitted to wetting and drying cycles. The field experiment was carried out in a coffee plantation in Piracicaba, SP, Brazil, on a soil classified as a Rhodic Kandiudalf, clayey texture. Using a neutron/gamma surface probe, θ and ρs were measured meter by meter along a 200 m spatial transect. Results showed that during the wet period there was no difference of spatial patterns of soil water content while during the dry period a difference of spatial patterns of soil water content data sets was observed. It was also observed that adjacent ρs observations present a higher spatial dependence range in the dry period as compared to the wet period. KEYWORDS: spatial and temporal variability, wetting/drying cycles, neutron/gamma surface probe. PADRÕES ESPACIAL E TEMPORAL DE MUDANÇAS DA UMIDADE E DENSIDADE DO SOLO NO CAMPO DURANTE PERÍODOS ÚMIDOS E SECOS RESUMO: Umidade (θ) e densidade do solo (ρs) influenciam importantes processos no solo e planta. Baseado neste fato, questões referentes à variabilidade espacial e temporal de θ e ρs para diferentes períodos do ano e diferentes fases de desenvolvimento da cultura do café tornam-se de extremo interesse. Este trabalho teve como objetivo caracterizar padrões espaciais e temporais de θ e ρs medidos na superfície do solo submetida a ciclos de umedecimento/secagem durante diferentes períodos do ano. O experimento foi conduzido em uma área cultivada com café pertencente a ESALQ/USP, Piracicaba/SP, em um solo classificado como Nitossolo Vermelho Eutrófico . Medidas de θ e ρs foram feitas metro a metro ao longo de 200 m usando uma sonda de superfície nêutron/gama. Resultados mostram que durante o período úmido não houve padrões de diferença espacial para θ enquanto que para o período seco o contrário foi observado. Foi também observado que observações adjacentes de ρs apresentaram uma faixa de dependência espacial maior no período seco quando comparado ao úmido. PALAVRAS-CHAVE: variabilidade temporal e espacial, ciclos de umedecimento/secagem, sonda de superfície nêutron/gama.
INTRODUCTION: Among the edaphic, the soil physico-chemical attributes in which the crop grows are of great importance because they affect directly the dry matter accumulation in different periods of the year and in all development phases of the crop. Tominaga et al. (2002) showed that on a tropical soil physical attributes of soil water content and bulk density greatly influence the important soil and plant processes such as water movement (Reichardt and Timm, 2004), soil compaction (Logsdon and Karlen, 2004), soil aeration (Stepniewski et al., 1994), and plant root system development (Boone and Veen, 1994). Based on this, questions related to the spatial and temporal variability of soil water content and bulk density during different periods of the year and different development phases of the coffee crop become of fundamental interest. Grayson et al. (1997), commented that an important question for hydrology is “how does the temporal variation in soil water content affect their spatial patterns”. Wendroth et al. (1999) monitored the soil water pressure heads in surface horizons at two field sites, a sandy loam and a heavy clay soil, between April and November 1995 in north-east Germany. They concluded that with decreasing soil water pressure head the variance of log10(-h) decreased to a critical value, for which a spatial correlation structure disappeared. On the other hand, with further drying, its variance increased again, and a spatial range of correlation appeared. Based on these facts, this work had as objective the characterization of spatial and temporal patterns of soil water content and bulk density at the surface soil layer when submitted to wetting and drying cycles during different climatic periods of year, in an area cultivated with coffee under a tropical climate. This information should help optimize the management of the coffee crop through appropriate fertilizer and cultural practices, or guide site-specific management. MATERIAL AND METHODS: The field experiment was carried out in a coffee plantation, belonging to ESALQ/USP, Piracicaba, SP, Brazil (22o 42’ S; 47o 38’ W, 580 m above sea level), on a soil classified as a Rhodic Kandiudalf, clayey texture (Embrapa, 1999). The coffee plants (variety Catuai Red IAC44) were planted in May 2001, in rows 1.75 m apart, with 0.75 m between plants. Using a neutron/gamma surface probe, soil water content and bulk density were measured meter by meter along a 200 m spatial transect. Measurements were made along the interrow which follows a contour-line, totaling 200 evaluations of each, during two distinct climatic periods: i. April to May 2003, a wet period: 1st measurement MW1: 04/24/2003; 2nd measurement MW2: 05/07/2003; 3rd measurement MW3: 05/23/2003; and ii. July to August 2003, a dry period: 1st measurement MD1: 07/04/2003; 2nd measurement MD2: 07/18/2003; 3rd measurement MD3: 08/02/2003. To evaluate soil water content θ (m3.m-3) and soil bulk density ρs (Mg.m-3) a neutron-gamma surface gauge (SG) was used. This gauge, Model MC-3, manufactured by CPN, is based on the neutron moderation, gamma attenuation and back scattering interactions in the soil. This gauge geometry allows θ and ρs evaluations within a semi-sphere of radius of about 0.15 m, located in the soil surface layer just below the probe. The SG was calibrated for this particular soil through a simulation of new parameters for the calibration equation (Cássaro et al., 2000), using soil bulk densities obtained by the volumetric ring (VR) method and the new soil bulk density values obtained by the SG, which were only 2 % different from those obtained by the VR. RESULTS AND DISCUSSION: Figs. 1A, C and E presents the spatial distribution, meter by meter, of the three soil water content data sets of the wet period (56.4 mm) along the 200 m spatial transect in the 0-0.15 m depth layer: MW1 04/24/2003 (Fig. 1A), MW2 05/07/2003 (Fig. 1C), and MW3 05/23/2003 (Fig. 1E). Each data set was first analyzed using classical statistics to obtain descriptive parameters such as means, standard deviations (SD) and coefficients of variation (CV). Fig. 1A (MW1), shows soil water content ranging from a maximum of 0.291 m3.m-3 to a minimum value of 0.144 m3.m-3, with an amplitude of 0.147 m3.m-3 and a mean of 0.210 m3.m-3. For MW2 (Fig. 1C), data ranged from 0.369 to 0.233 m3.m-3 with a mean of 0.304 m3.m-3, and for MW3 (Fig. 1E) the mean value of 0.179 m3.m-3.was found, corresponding to the lowest soil water contents measured along the spatial transect in the rainy period. To verify whether precipitation events change the spatial correlation structure among the adjacent θ observations in the wet period, autocorrelograms of each spatial series were calculated (Nielsen and Wendroth, 2003). Figs. 1B, D and F presents the spatial dependence of θ data sets in relation to their neighborhood for different dates.
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Figure 1. Soil water content θ (m3.m-3) distributions along the transect and autocorrelation functions (ACF) for soil and θ data sets for dates: (A-B) MW1 (04/24/2003); (C-D) MW2 (05/07/2003); and (EF) MW3 (05/23/2003). Fig. 1B (MW1) shows that adjacent θ observations are spatially dependent up to 2 m (2 lags in this study), i.e., based on the t test at the 5 % probability level observations separated by a distance of less than 2 m would be expected to yield approximately equal values of soil water content. For the date of MW2 (Fig. 1D) in which the highest θ values were measured θ at any location is representative for a nearly 10-m circular domain. Fig. 1F indicates that adjacent θ observations on MW3 are spatially dependent up to 4 m using the same statistical test. Analyzing Figs. 1B, D and F it is not possible to identify a relation between the soil water content and the spatial pattern of θ along the transect for the wet period since the spatial correlation structure presented in Figs. 1D (MW2) and 1F (MW3) were similar. Simultaneously to θ measurements, soil bulk density (ρs) data sets were also obtained, meterby-meter, along the spatial transect at the same depth and dates. The autocorrelation function ACF for the ρs data sets are shown in Fig. 2. From Figs. 2A to C, using based on the t test at 5 % probability, it can be verified that adjacent ρs observations are spatially correlated only up to 1 m for the dates of MW1 (Fig. 2A) and MW2 (Fig. 2B), with no spatial correlation for ρs at MW3 (Fig. 2C), indicating a random behavior at this date. The same θ and ρs analysis were made for the dry period (18.6 mm):
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dates of MD1 (07/04/2003), MD2 (07/18/2003), and MD3 (08/02/2003). The results showed that adjacent ρs observations present a higher spatial dependence range in the dry period as compared to the wet period. This fact was also observed for the θ measurements. From the soil water content autocorrelograms shown for wet (Figs. 1B, D and F) and dry (not presented here) periods it is verified that the spatial correlation structure of θ measurements is not unique along the transect for the different dates, i.e., it is time-dependent, not being unique within the field. This can be attributed to the fact that θ is rarely in hydraulic equilibrium in the soil profile, being constantly under redistribution within the profile as a result of plant root extraction, evaporation and infiltration at the soil surface. Therefore, autocorrelograms of soil water properties and attributes are not expected be unique within a field (Nielsen and Wendroth, 2003). 0.40
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Figure 2. Autocorrelation functions ACF for soil bulk density (ρS) sets for dates: (A) MW1 (04/24/2003); (B) MW2 (05/07/2003); and (C) MW3 (05/23/2003). CONCLUSIONS: Results showed that during the wet period there was no difference of spatial patterns of soil water content while during the dry period a difference of spatial patterns of soil water content data sets was observed. It was also observed that adjacent ρs observations present a higher spatial dependence range in the dry period as compared to the wet period. Both results can be associated to precipitation events altering therefore spatial correlation structure among soil water content adjacent observations as well as among soil bulk density adjacent observations. REFERENCES: Boone, F.R., Veen, D.E., 1994. Mechanisms of crop responses to soil compaction. In: Soane, B.D., Van Ouwerkerk, C. (Eds.) Soil compaction in crop production. New York: Elsevier. pp. 237-264. Cássaro, F.A.M., Tominaga, T.T., Bacchi, O.O.S., Reichardt, K., Oliveira, J.C.M., Timm, L.C., 2000. Improved laboratory calibration of a single-probe surface gamma-neutron gauge. Aust. J. Soil Res. 38, 937-946. EMPRESA BRASILEIRA DE PESQUISA AGROPECUÁRIA-EMBRAPA. Centro Nacional de pesquisa de Solo. Sistema Brasileiro de Classificação de solos. Brasília: CNPS, 1999. 412p. Grayson, R.B., Western, A.W., Chiew, F.H.S., 1997. Preferred states in spatial soil moisture patterns: local and nonlocal controls. Water Resour. Res. 33, 2897-2908. Logsdon, S.D., Karlen, D.L., 2004. Bulk density as a soil quality indicator during conversion to notillage. Soil Till. Res. 78, 143-149. Nielsen, D.R., Wendroth, O., 2003. Spatial and temporal statistics: sampling field soils and their vegetation. Reiskirchen: Catena Verlag. 398p. Reichardt, K., Timm, L.C., 2004. Solo, planta e atmosfera: conceitos, processos e aplicações. Barueri: Manole. 478p. Stepniewski, W., Glinski, J., Ball, B.C., 1994. Effects of compaction on soil aeration properties. In: Soil compaction in crop production. New York: Elsevier. pp. 167-169. Tominaga, T.T., Cássaro, F.A.M., Bacchi, O.O.S., Reichardt, K., Oliveira, J.C.M., Timm, L.C., 2002. Variability of soil water content and bulk density in a sugarcane field. Aust. J. Soil Res. 40, 605-614. Wendroth, O., Pohl, W., Koszinski, S., Rogasik, H., Ritsema, C.J., Nielsen, D.R., 1999. Spatiotemporal patterns and covariance structures of soil water status in two Northeast-German field sites. J. Hydr. 215, 38-58.
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