Abstract:
Cassava (Manihot esculenta Crantz) is an important food crop in the world, so nutrient management is necessary to increase the product of cassava to meet the consumption. Nitrogen (N) potassium (K) and sulfur(S) are required nutrients and promote productivity for cassava especially nitrogen. However, the application of nitrogen fertilizer may result in the change of potassium and sulfur form in the soil and those nutrient uptakes. The objective of this study was therefore to study the effect of nitrogen fertilizer rates on the transformation of nitrogen, potassium, and sulfur in soil and the interaction effects of nitrogen-potassium and nitrogen-sulfur on the growth and nutrients uptake of cassava. The study was divided into three experiments. Experiment 1: the study of the influence of nitrogen fertilizer rates on the transformation of nitrogen, potassium, and sulfur in sandy soil. Soil samples after harvesting from the experiment on the title the response of cassava to nitrogen fertilizer rates experiment in the research project title of development of nitrogen, phosphorus and potassium fertilizer rates. The experimental design was split plot with 3 replications. The soil after planting for cassava of 0-30 and 30-60 cm depth was analyzed nitrogen, potassium and sulfur form. Experiment 2 and 3 were conducted in a
greenhouse at the Faculty of Agricultural Technology, King Mongkuts Institute of Technology Ladkrabang. The experimental design was a 3×3 factorial arrangements in a randomized complete block design (RCBD) with 4 replications. Experiment 2; effects of interaction between nitrogen and potassium on the growth and nutrients uptake of cassava. Three different nitrogen rates (500 (N1), 1000 (N2) and 1500 (N3) μmol/L) were combined with three different potassium rates (500 (K1), 1000 (K2) and 1500 (K3) μmol/L). Experiment 3; effects of interaction between nitrogen and sulfur on the growth and nutrients uptake of cassava. Three different nitrogen rates same as experimental 2 were combined with three different sulfur rates (500 (S1), 1000 (S2) and 1500 (S3) μmol/L). The results from experiments 1 show that different rates of nitrogen fertilizers affect organic-N at 0-30 cm depth. Organic-N at the nitrogen fertilizer rate of 24 kg/rai was 624.77 mg/kg which significantly higher than the without nitrogen fertilizer treatment as 389.56 mg/kg. Moreover, the
nitrogen fertilizer application rate affected potassium content in the exchangeable-K form at 0-30 cm. Exchangeable-K in nitrogen fertilizer at the rates of 8 and 24 kg/rai were 32.23 and 30.90 mg/kg, respectively which significantly difference with a nitrogen fertilizer at the rate of 16 kg/rai (22.86 mg/kg). Total-K in without nitrogen fertilizer treatment was 1,737.1 mg/kg which highly significant with total-K in nitrogen fertilizer treatment at the rate of 16, 24, and 32 kg/rai as the values 1,328.8, 1326.4 and 1,206.4 mg/kg, respectively. While different rates of nitrogen fertilizers affected organic-S and total-S sulfur at 30-60 cm depth. Organic-S and total-S were highly significant with and without nitrogen fertilizer were 164.64 and 167.63 mg/kg, respectively and lowest at nitrogen fertilizer at the rate of 24 kg/rai were 69.01 and 71.20 mg/kg, respectively. The experiments 2 show that increasing nitrogen rates (Treatment N3) significantly increased plant height (206.92 cm), SPAD value of the upper and lower leaf (42.34 and 34.64), the total fresh and dry weight (1,101.62 and 339.48 g/plant). In addition, increasing nitrogen rates affected the concentration of nitrogen concentration in the youngest fully-expanded leaves, nitrogen uptake in all plant organs, potassium uptake in leaf blade, tuber and total uptake. While the concentration of total calcium, total magnesium, total manganese, total copper, and total molybdenum decreased significantly with increasing nitrogen fertilizer rates. Different potassium fertilizer rates affected the SPAD values in the lower leaves of cassava. SPAD values in the lower leaves highest in K2 were 33.75. In addition, increasing potassium rates affected nitrogen uptake in OSC, tuber and potassium uptake in all plant organs except leaf. Nitrogen and potassium uptake in leaf blade, stem+petio and tuber had a high positive correlation significantly with the correlation coefficient (r) was 0.86**, 0.84** and 0.87**, respectively. The positive correlation
significantly between nitrogen uptake with a fresh and dry weight of all plant organs except old stem cutting (OSC). The correlation coefficient (r) for fresh weight in the range of 0.40*- 0.82** and 0.35*-0.85** in dry weight. In addition, the results found that nitrogen uptake was positively correlated with potassium uptake in leaf, stem+petio, and tuber with a correlation coefficient in the range of 0.84 ** - 0.87 **. The experiments 3 show that increasing nitrogen rates (Treatment N3) significantly increased plant height (266.33 cm), SPAD value of the lower leaf (34.90), the total fresh and dry weight, (1,274.03 378.64 g/plant). In addition, increasing nitrogen rates affected the concentration of nitrogen and sulfur in youngest fully-expanded leaves, nitrogen uptake in leaf blade, tuber, root and total nitrogen uptake, sulfur uptake in leaf, tuber, root and total sulfur uptake. While the concentration of calcium, magnesium, manganese, copper, and molybdenum in the youngest fully-expanded leaves decreased significantly with increasing nitrogen fertilizer rates. Increasing sulfur rates (Treatment S3) affected the fresh and dry weight of tuber were 281.06 and 114.28 g/plant. In addition, increasing sulfur rates significantly increased the concentration of sulfur in the youngest fully-expanded leaves, total nitrogen uptake sulfur in root and total sulfur uptake. While the concentration of molybdenum decreased with increasing sulfur fertilizer rates. Nitrogen
and sulfur uptake in leaf blade, stem+petio and tuber had a high positive correlation significantly with the correlation coefficient were 0.97**, 0.68** and 0.96**, respectively. In addition, the results found that the positive correlation between nitrogen uptake and fresh and dry weight all plant organs were highly significant with the range of 0.48**- 0.76** and 0.37*- 0.74** for fresh and dry weight, respectively. Nitrogen and potassium uptake in leaf blade, stem+petio and tuber were positively correlated with statistically significant correlation coefficient at 0.67**- 0.98**.