Reducing fertilizer use in cabbage production with a combined high speed ridger and double banding fertilizer applicator

Abstract

Banding fertilization supplies nutrients to plant more effectively than broadcast fertilization. However, when fertilizer is too close to the plants, the high concentration of salts affects them adversely. On the other hand, when it is too far from the plants, plant growth is delayed. Coated fertilizers have solved these problems. Many researchers have shown that band placement of slow-release coated fertilizers increases nitrogen use efficiency and cabbage (Brassica oleracea var. capitata) yields, making possible a reduced application of fertilizer. But coated fertilizers leave microplastics in the soils, which is a disadvantage. We should refrain from using coated fertilizers containing plastic. Therefore, we cultivated cabbage by using a newly developed double layer banding applicator and compound fertilizer. Using this machine, a small amount of NPK is fertilized in the upper layer and the rest in the lower layer, perhaps making possible a reduced application of fertilizer.

Four field experiments were conducted at the National Agriculture and Food Research Organization (NARO) farm in Tsukuba between 2021 and 2023, to examine the effects of double banding fertilization (upper and lower layers) and reduced application of fertilizers on spring sowing (2022 and 2023) and summer sowing (2021 and 2023) cabbage yields. A newly developed, combined high speed ridger and double banding fertilizer applicator was used (upper layer 0-5 cm depth and lower layer about 15 cm depth). The current recommendation (N-P₂O₅-K₂O) for cabbage in Ibaraki prefecture indicates a 250-250-250 kg ha^-1 split application (preplanting broadcast of 200 kg ha^-1 and top dressing of 50 kg ha^-1 on the row several weeks after planting). It was treated as a control. In the experiments we used a NPK compound fertilizer (14-14-14) and the cabbage variety ‘Okina SP’ (Takii & Co., Ltd.). The soil was classified as Allophanic andosols. The test treatments of fertilizer application reduced by 30% were: broadcast (four-fifths of total fertilizer before planting and one-fifth after planting); and double banding (one-fifth of total fertilizer in the upper layer and four-fifths in the lower layer). As additional treatments, a 50% reduction of double banding application using 14-14-14 or a manure containing chemical fertilizer ‘Ecolet’ (Asahi Agria Co., Ltd.) in the lower layer were included in the 2023 spring and summer sowings. All treatments had three replicated plots. Cabbage seedlings grown for five weeks were transplanted. Spacing between rows was 0.6 m and spacing within rows was 0.4 m. At harvest, 15 or 16 plants per plot were sampled. Cabbage head weight, height, and diameters of the long and short axes were measured. Multiple comparisons between treatments were made by Tukey-Kramer test.

The results showed that when the amount of fertilizer applied was reduced by 30%, double banding (regardless of lower fertilizer type) produced equal cabbage yields in spring and summer sowing as that of the control treatment in four experiments, although broadcast fertilization decreased yields in three experiments. When fertilizer application was reduced by 50%, the spring sowing yield decreased significantly but the summer sowing yield did not decrease, regardless of the lower fertilizer type. In summary, the double layer banding application of NPK compound fertilizer improved the efficiency of fertilizer use and made it possible to reduce the amount applied by 30% and to omit a split application in cabbage cultivation.