The effect of chemical, organic, biological and integrated fertilizer systems on soil fertility and nutritional status of rapeseed (Brassica napus L.)

Overused chemical fertilizers not only is associated with negative impacts on the environment and human health, but also by reducing of agricultural lands yield and crops quality. Therefore, the combined use of organic fertilizers with chemicals ones has been considered as a method of integrated plant nutrition management. The objective of this study was to investigate the effect of separate and combined application of different organic, biological and chemical fertilizers on the concentration of nutrients in the seeds and leaf of transplanted rapeseed (Brassica napus L.) and soil under cultivation.

An experiment in a randomized complete block design with eleven treatments and three replications in the field crop year 2019-2020 on the lands of the Iraqi Agricultural Research Station (IARS) in Gorgan (Gorgan, northern Iran) was performed. Treatments included: 1) Control (T1), 2) NPK chemical fertilizer (T2), 3) NPK+Fe+Zn chemical fertilizers (T3), 4) poultry manure (T4), 5) Compost (T5), 6) Biofertilizer + Fe and Zn chemical fertilizers (T6), 7) NPK chemical fertilizer+ humic acid (T7), 8) 50% poultry manure + 50% Compost + 50% NPK+ Fe and Zn chemical fertilizers (T8), 9) 25% poultry manure + 25% Compost + 100% NPK + Fe and Zn chemical fertilizers (T9), 10) 50% poultry manure + 50% Compost + 50% NPK + Fe and Zn chemical fertilizers + Biofertilizer (T10) and 11) direct sowing of seeds + NPK chemical fertilizer (T11). At the end of the cultivation period, macroelements (N, P, K) and microelements (Fe and Zn) in plants and soil were measured.

The results showed that the application of biofertilizer + Zn + Fe (T6) increased the production of N and soil phosphorus, and decreased pH and EC and the combined application of organic and biofertilizers with chemical fertilizers (T8, T9 and T10) increased the availability of K, Fe and Zn in soil. Also, application of biofertilizer + Fe + Zn (T6) caused a significant increase (P<0.05) in N, P, K and Zn on the leaf and also the content of N, P and K of seed compared to other treatments and control by the lowest amount of these elements. Concentrations of Fe in rapeseed leaf and seeds increased significantly (P<0.05) compared to the control treatment with the combined use of organic and biological and chemical fertilizers (T8, T9 and T10).

T6, T8, T9 and T10 treatments were the most effective treatments in increasing nutrient production and nutritional needs of rapeseed. Therefore, the combined application of chemical fertilizers with organic and biofertilizers probably due to the improvement of physical conditions, biodiversity and availability of plant nutrients, caused soil fertility, environmental health and rapeseed nutritional needs.