Additive intercropping of sunflower and soybean to improve yield and land use efficiency: Effect of thinning interval and nitrogen fertilization

摘要

An additive intercropping model was adopted to improve land use efficiency and productivity of two prominent oil crops grown in Egypt, that is, sunflower (Helianthus annuus L.) and soybean (Glycine max [L.] Merr.) A 2-yr field trial was conducted in Northern Egypt during the summers of 2017 and 2018. The effects on yield, crop components, and land use efficiency of the system were tested with three N fertilizer rates (70, 105, and 140 kg N ha-1) and three thinning intervals of 15, 30, and 45 d after sowing (DAS) for sunflower and 30, 45, and 60 DAS for soybean. Late thinning increased plant height in both crops, but reduced sunflower stem and head diameters and seed weight per head. The maximum seed yield occurred in the pure stands and reached 4.00 and 1.61 t ha-1 for sunflower and soybean, respectively. Early thinning positively affected seed yield and fresh and dry biological yields, while the effect of N rates was limited. Seed oil content of both crops was slightly affected by the treatments and generally averaged approximately 50% and 20% in sunflower and soybean, respectively. While the land equivalent ratio (LER) indicated the advantage of intercropping sunflower and soybean (LER 1), the DM equivalent ratio (DMER) provided a more realistic estimate as to the effect of intercropping compared with sole cropping in an additive model. Early and intermediate thinning intervals across all N fertilizer rates resulted in yield gain (DMER 1), while late thinning reduced yield (DMER 1). Intercropping sunflower and soybean crops is recommended for low input farming systems, particularly in developing countries.