Effect of chemical fertilizer and humic acid on cabbage leaves' N, P, K and S concentrations (Brassica oleracea var. capitata L.)

A field study was carried out in one of the fields of Jdeidet Al-Shatt district is, located 30 km from the center of Baquba in Diyala governorate, during the autumnal season 2021-2022 on silty loam soil classified to a level under the Typic Torrifluvent according to the modern American classification to know the effect of adding chemical fertilizer and humic acid on the availability of nitrogen, phosphorus and potassium concentrations for cabbage leaves, according to of randomized complete block design (RCBD) by using three replicates. The first factor was the chemical compound fertilizer NPK( 20:20:20 ) added at three different levels 0, 150 kg ha-1, 300 kg ha-1, while the second factor was humic acid at three levels 0, 15 kg ha-1, 30 kg ha-1. Fertilizers were added to the soil by making an incision around the plant and were added in two stages, the first when planting and the second 43 days after the date of the first batch. The results of the study showed that adding chemical fertilizer at a level of 300 kg ha-1 led to significant differences in the concentrations of nitrogen, phosphorous, potassium and sulfur elements in the inner leaves, where the concentrations of elements reached 2.55%,0.34%, 2.95%,1.36% respectively, the outer leaves. In contrast, the concentrations of nitrogen, phosphorous and potassium reached 4.00 %, 0.34%, and 2.67%, respectively, While the superiority of the humic acid at the level of 30 kg ha-1 to 2.33%, 0.32%, 2.77%,1.47% in the inner leaves, respectively, while in the outer leaves 3.80 %,0.31 %,2.49%.
 
Keywords: chemical fertilizer, humic acid, concentrations of N,P, K and S, cabbage.