Impact of soil water regimes and partial root-zone drying in field-grown papaya in semi-arid conditions.

This study aimed to evaluate in the papaya Tainung genotype, the effects of partial root-zone drying (PRD) technique on soil water regimes by using different frequencies of shifting irrigation-side of plant row and the effects of PRD technique on (1) crop agronomic performance, (2) titratable fruit acidity (TA), (3) total soluble solids (TSS), and TSS/TA ratio. Also, we analyze the spatial dynamic of papaya condition using normalized difference vegetation index (NDVI) from different satellite images. The study was conducted in the semi-arid region of Bahia (BA) and Minas Gerais (MG), Brazil. The combination of 100% (Full irrigation-FU), 50%, and 35% in the irrigation depth (WID) and frequencies of shifting plant-row side irrigation of 0 (Fixed Irrigation-FX), 7, 14, and 21 days were applied. Nine treatments were studied in BA and five in MG. The water available in the soil was reduced to 44% for frequencies of shifting plant-row side irrigation of 7 days, 50% for 14 days, and 85% for 21 days, compared to the soil water availability at field capacity. Partial water deficit in the soil through the PRD technique did not significantly reduce the total root length, effective root depth, and root effective horizontal distance of the papaya Tainung genotype. However, PRD treatments showed leaf abscission, which resulted in reduced leaf area and NDVI values, especially in the MG experiment. Papaya yield and fruit quality were not affected. However, except for PRD 21 35%, irrigation water depth reduced to 50 and 35% under PRD increased crop water productivity (CWP) in papaya plants. Thus, the PRD technique may save 35% of WID using the alternation of lateral shift irrigation of crop row every 7 days under water scarcity in semi-arid regions. The NDVI index was important to compare the papaya canopy vigor between the experimental areas studied. We also confirmed the potential of NDVI to monitor the vigor of papaya canopy, since we could notice the sensibility of NDVI to identify water stress in papaya in higher vapor pressure deficit (VPD) conditions occurred in October 2016 and January 2017 in Bom Jesus da Lapa-BA. Therefore, the PRD strategy can be a useful tool to save water in papaya cultivation under semi-arid conditions.

Salinity reduces nutrients absorption and efficiency of their utilization in cassava plants / Salinidade reduz a absorção e a eficiência de utilização de nutrientes em plantas de mandioca

ABSTRACT: The objective of this research was to evaluate the influence of salinity on the absorption and utilization of nutrients by cassava. For the study, cassava was submitted to four saline concentrations: 0, 20, 40, and 60mM NaCl. Results showed that the absorption of all nutrients, except nitrogen (N), was reduced by salinity, with highest reduction for potassium (K). However, all nutrients were maintained at concentrations which did not indicate mineral deficiency problem. The abnormal concentration of calcium in the tuberous roots may have been one of the factors that contributed to the lower growth of this organ and of the plant as a whole. Transports of nitrogen, potassium, phosphorus and sulfur from root to the aerial part was higher under salinity treatment. Efficiency in the use of all the nutrients, mainly N, was reduced due to salinity. Given that: (i) the absorption of K was the most impaired, (ii) there was abnormal accumulation of Ca in tuberous roots, and (iii) the efficiency in the use of N was the most affected, it is suggested to prioritize studies on these three issues, as a way to better understand the aspects related to the tolerance/sensitivity of cassava plants to salinity.

RESUMO: O objetivo deste trabalho foi o de avaliar a influência da salinidade sobre a absorção e utilização de nutrientes pela mandioca. Para o estudo, as plantas foram submetidas a quatro concentrações salinas: 0, 20, 40 e 60mM de NaCl. Os resultados mostraram que a absorção de todos os nutrientes, exceto o nitrogênio (N), foi reduzida pela salinidade, com maior redução para o potássio (K). No entanto, todos os nutrientes foram mantidos em concentrações que não indicaram problema de deficiência mineral. A concentração anormal de cálcio nas raízes tuberosas pode ter sido um dos fatores que contribuíram para o menor crescimento desse órgão e da planta como um todo. Os transportes de nitrogênio, potássio, fósforo e enxofre da raiz para a parte aérea foram maiores sob tratamento com salinidade. A eficiência no uso de todos os nutrientes, principalmente N, foi reduzida devido à salinidade. Considerando que: (i) a absorção de K foi a mais prejudicada, (ii) houve acúmulo anormal de Ca nas raízes tuberosas e (iii) a eficiência no uso de N foi a mais afetada, sugere-se priorizar estudos sobre estas três questões, como forma de melhor entender os aspectos relacionados à tolerância/sensibilidade das plantas de mandioca à salinidade.

Distribuição da umidade num perfil de solo irrigado por gotejamento superficial e subsuperficial / Humidity distribution in a soil profile irrigated by surface and buried drip systems

Conduziu-se o presente trabalho com o objetivo de avaliar a distribuição de água no perfil de um Latossolo cultivado com mamoeiro do grupo Formosa, irrigado por dois gotejadores por planta instalados a 0,30 m da mesma. Usou-se gotejamento superficial com emissores de vazão de 3,75 L.h-1 e subsuperficial com emissores de vazão foi 2 L.h-1 a 0,25 m de profundidade. Os valores de umidades foram obtidos por meio de sondas de TDR instaladas e distribuídas em perfis de solo. As leituras foram realizadas em intervalos de dez minutos, durante dois ciclos de irrigação, utilizando um sistema de aquisição de dados composto por uma TDR, um datalogger e quatro multiplexadores. Os dados foram analisados a partir de isolinhas de distribuição de umidade e os resultados mostraram que o sistema de gotejamento subsuperficial apresentou uma menor variação da umidade concentrada na direção do sistema radicular do mamoeiro e o armazenamento de água no sistema subsuperficial foi 17 por cento superior ao superficial.

This work aimed at evaluating water distribution in a Latossol profile cultivated with papaya of Formosa group, irrigated by two drippers per plant installed at 0.30 m from the plant. Surface drip irrigation with emitters of 3.75 Lh-1flow rate and subsurface drip with emitters of 2 Lh-1 at 0.25 m depth were used. The humidity values were obtained by means of TDR probes installed and distributed in soil profiles. The readings were performed in a ten-minute interval during two irrigation cycles, using a data acquisition system composed by a TDR, one datalloger and four multiplexers. The data were analyzed from isolines of humidity distribution and results showed that the subsurface drip system had a smaller variation of humidity concentrated in the direction of papaya root system. The water storage for the subsurface system was 17 percent larger than the one for surface system.