Case Study on the Use of the Leaf-Count Method for Drip Fertigation in Outdoor Cucumber Cultivation in Reconstructed Fields Devastated by a Tsunami

Drip fertigation was tested in fields using a nitrogen fertilization method based on leaf increments, with the aim of increasing the cucumber yield in outdoor fields restored after the tsunami disaster in Rikuzentakata City, Iwate Prefecture, in 2011. The 2016 test site (Takata field) was restored as a paddy field, and there were problems with water retention and gravel contamination. The condition of the 2017 test site (Yonesaki field) was better than that of the 2016 site. The drip fertigation method increased cucumber yield by 93% and 27% in the Takata and Yonesaki fields, respectively, when compared to the yield from fields cultivated conventionally. Drip fertigation enables the constant supply of liquid fertilizer to the rhizosphere, and the easy application prevents the scarcity of fertilizer, especially at later stages of growth. In contrast, a real-time soil diagnosis, using the Dutch 1:2 soil–water extract method, was unsuccessful due to flooding, especially in the Takata field. As the purpose of this method is not to reduce the amount of nitrogen provided, but to increase the yield, and because it is difficult to precisely control the application of fertilizer due to precipitation, we suggest that the real-time soil diagnosis and feedback should be omitted to further simplify fertilizer application.

Determination of dissolved reactive and dissolved total phosphorus in water extract of soils

The simplified acid peroxydisulphate digestion of soil water extract was evaluated for determination of total dissolved phosphorus by molybdenum-blue colorimetry in comparison with direct P-detection in water extract by the ICP-AES technique. The research was conducted on 79 agricultural soils with different agrochemical characteristics. The results of the colorimetric P detection in water extract without digestion and ICP phosphorus detection were different. The median of values determined by ICP-AES was 1.7 times higher than that of colorimetry, but the correlations between the two measurements were quite close (r = 0.993). Differences between the colorimetric phosphorus and ICP-AES phosphorus were irregular, increasing as the phosphorus level in soils decreased. The simplified procedure of acid peroxydisulphate digestion is useful for routine determination of total water-extracted phosphorus in soils when the soil testing laboratory is not equipped with the ICP-AES technique. The two-tailed paired t-test did not prove any difference in the values between the direct ICP-AES P-detection in water extract of soils and colorimetric P-detection in the acid peroxydisulphate digest.  

Sodicity in irrigated soils in Saskatchewan: Chemistry and structural stability

Irrigation with sodic waters may damage soil structure, but neither the processes involved nor the critical levels of exchangeable Na have been well defined for prairie soils. We examined two irrigated soils from southern Saskatchewan on which sodicity damage had occurred to determine the processes and the chemical conditions (exchangeable Na and electrolyte concentration) that cause structural damage. Dispersion of clays in the upper 20 cm of the profile seemed to be the primary cause of structural deterioration. Examination of irrigated soil by scanning electron microscopy (SEM) showed that sand- and silt-size grains were stripped of binding colloidal particles and that large pore spaces had formed, creating very loose aggregates. In one of the soils, physical instability was observed at an exchangeable-Na percentage (ESP) of only about 10%, indicating that some soils in Saskatchewan are relatively sensitive to sodicity. With a 1:5 (wt vol−1) soil/water extract, the electrical conductivity (EC) needed to prevent clay dispersion when soil suspensions were mechanically agitated was about 0.2 dS m−1 in the absence of Na, increasing to 1.5–2 dS m−1 at a sodium adsorption ratio of 20 (mmolc L−1)0.5. Sodic conditions greatly altered soil chemical behavior, with the most sodic soil having an extremely high level of water-extractable P. In a laboratory experiment, addition of Ca (as CaCl2 or gypsum) to replace Na reduced water-extractable P from 78 mg kg−1 to less than 20 mg kg−1. The effect of sodicity on P solubility was likely due to a decrease in surface electrostatic potential as exchangeable Na increased. Increased solubility of P along with the potential for runoff and erosion from Na-affected soils could result in increased inputs of P to surface waters. Key words: Sodicity hazard, clay disperson, phosphate solubility

Seasonal variation of pH, aluminium, and manganese in acid soils from north-eastern Victoria

Seasonal variation in pH (measured in H2O or 0.01 mol CaCl2/L) and in Al and Mn extracted by 0.01 mol CaCl2/L are reported for north-eastern Victoria. Seasonal variation in pH(H2O) was significantly (P<0.05) greater than either the spatial variation or laboratory error. There was no significant (P<0.05) seasonal variation in pH(CaCl2). For pH (H2O), values were observed to increase after the autumn break, to peak at or near midwinter, and to decrease slowly over the spring and summer months to lowest values in late summer. Seasonal changes for pH(H2O) were significantly (P<0.05) related to the ionic strength of the 1 : 5 soil : water extract. Significant seasonal variations (P<0.05) occurred for extractable Al and Mn in a podsolised red earth and a red podsolic. Seasonal effects were a significant (P<0.05) source of variation for the methods used in this study and should, therefore, be considered in any comparative or predictive studies using these methods.

Simple water-balance models for simulating moisture, salinity and sodicity profiles in soils under wheat

SUMMARYExperiments were conducted in wheat planted in microplots at Hisar and Sirsa in Haryana state, India, to observe and simulate the depth distribution of moisture content, electrical conductivity in 1:2 soil-water extract (EC 1:2), and exchangeable sodium percentage (ESP) of soils after irrigation with water of high electrical conductivity (12–19 dS/m) and sodium adsorption ratio (20–80 (mmol/1)0·5). The three simulation models used differed in the procedure of estimation of evapotranspiration (models I and II, Reddy 1983; model III, Arora et al. 1987). In general, the means of the experimental moisture content profiles decreased and those of EC 1:2 and ESP increased with irrigation at both locations. Statistical analysis showed an overall good agreement between the experimental and simulated values of moisture content, EC 1:2 and ESP; the accuracy of simulation of the models followed the order model II = model III > model I, for moisture content and EC 1:2, but was identical for ESP.