Effects of band placement and nitrogen rate on dry matter accumulation, yield and nitrogen uptake of cabbage, carrot and onion

Abstract

Adequate nitrogen (N) nutrition is essential for producing high vegetable yields of good quality. Fertilizer N not taken up by the plants is, however, economically wasteful and can be lost to the environment. Therefore the efficient use of N fertilizer, involving accurate estimation of crop N demand, choice of application method and timing of N fertilization, is an important research area. The effects of band placement and rate of N fertilization on inorganic N in the soil and the dry matter accumulation, yield and N uptake of cabbage, carrot and onion were studied in a three-year field experiment between 1993 and 1995. The plants were sampled during the growing season to determine the dry matter accumulation and plant N concentration. The inorganic N in the soil was determined during the growing period and after harvest. The N uptake was 3.8 kg, 1.6 kg and 2.5 kg per ton of edible yield of cabbage, carrot and onion, respectively. At the highest yield levels the N uptake including crop residues was 300 kg ha-1, 150 kg ha-1 and 120 kg ha-1 in cabbage, carrot and onion, respectively. In cabbage, almost 50% of N was in crop residues, whereas in carrot and onion only about 30% of N was in crop residues. Nitrogen uptake from non-fertilized soil varied from 29 to 160 kg ha-1, depending on the growing season and the crop. Cabbage and carrot utilised soil N efficiently, usually taking up more than 100 kg ha-1 from non-fertilized soil. Onion, on the contrary, utilised soil N relatively poorly, usually less than 50 kg ha-1 from non-fertilized soil. The rate of N uptake was low with all crops in early summer. After one month, N uptake increased in cabbage and onion. This uptake continued until harvest, i.e. mid-August for onion and early September for cabbage. Nitrogen uptake by carrot started rapidly only two months after sowing and continued until harvest at the end of September. High N rates often resulted in high N concentrations and N uptakes, but growth was not necessarily increased. One month after fertilization, most of the N placed was still near the original fertilizer band and at the depth of 5-10 cm. At that time, broadcast N was at a depth of 0-5 cm. After harvest the soil mineral N content was generally low, i.e. below 25 kg ha-1 at the depth of 0-60 cm. Onion was an exception with poor growth in 1994, when soil mineral N after the highest N rate was 80 kg ha-1 at a depth of 0-60 cm after harvest. The placement distance in the cabbage experiment, 7.5 cm in the side and 7 cm below cabbage transplants, resulted in lower plant growth and N uptake than broadcasting of N at the beginning of the growing periods 1993 and 1994. Towards harvest differences between application methods decreased, although in 1993, placement of N still led to 6% lower cabbage yields than broadcasting of N. In 1993, high N rates increased cabbage dry weight and N uptake towards harvest, and this effect was more pronounced when N was broadcast. In 1994, soil N mineralisation was high, and only non-fertilized cabbages took up less N than fertilized plants. Carrot was remarkably insensitive to N fertilization. Carrot yields were similar with and without N fertilizers. Band placement and N rate did not affect carrot growth and N uptake. In 1993, band placement and high rates of N increased onion growth and bulb yield more than broadcasting. In 1994, onion growth was poor and treatments did not affect plant N concentrations or growth. Apparent recovery of fertilizer N was increased in 1993 by low N rates or band placement. This result that band placement of N does not much affect vegetable growth is in agreement with most previous studies. With onion, probably due to the sparse root system, positive effects of N placement are most likely to be found.;