CROP RESPONSES TO APPLIED MOLYBDENUM AND COPPER ON PODZOL SOILS

Abstract

Experiments were conducted to determine the response to applied Mo and Cu of several crops grown on selected Podzol soils under greenhouse conditions. An application of Mo resulted in percent yield increases of 2000–5000 for cauliflower, 400–900 for spinach, 20–400 for barley, 90–400 for timothy, and 150–400 for alfalfa, depending on the soil series. The average Mo contents of these crops ranged from 0.05 to 0.85 from the untreated soils, and from 0.64 to 6.62 ppm from the Mo-treated soils, respectively. After the harvest of the last crop, 81 to 86% of the applied Mo was accounted for in the crop tissues and as exchangeable Mo in the soil. The original exchangeable Mo content of soils and the Mo content of crops from Mo-treated soils showed highly significant positive correlation coefficients with the yields of crops grown on untreated soils, and were negatively correlated with the yield response to Mo treatment.None of the four crops tested responded significantly in yield to applied Cu, although there was an increase in kernel yield of Hudson barley on three of the investigated soils. The Cu content of plant tissues, however, increased by about 50% in spinach and Herta barley straw, and 400% in Hudson barley kernels, as a result of Cu application. The average Cu contents of spinach, Herta and Hudson barley kernels, and alfalfa ranged from 2.5 to 8.5 and from 6.6 to 13.2 ppm from the untreated and Cu-treated soils, respectively. These Cu contents appeared to be in the optimum range. After the harvest of the last crop, 85 to 94% of the applied Cu was recovered from the plants and as exchangeable Cu in soils. There was no apparent relationship between the exchangeable Cu content of soils and the Cu content of the crops.