Effect of phosphate fertilizer on yield and nutrient uptake by girasole (Helianthus tuberosus) under irrigation with seawater in Laizhou' sea beach

Seawater irrigating agriculture is one of effective measures in reasonable using and exploitating seawater, saline soils and salt-tolerant plants. In 2003, the field experiments were carried out to study the effect of phosphate fertilizer on girasole (Helianthus tuberosus) irrigated with different concentration of seawater in mudflat along the coast of Laizhou (Shandong Province). The results were as follows: 1) The increased yields of tuber and aerial parts were more in the treatment with phosphorus fertilizer with the seawater irrigation than in the treatment with the fresh water. The effect of phosphate fertilizer on yield increased with increasing of seawater concentration and was largest in the treatment with irrigation of 50% seawater (W3). For example, the tuber yield in the treatments with P2(P2O5 30 (kg/hm2)), P3 (P2O5 60 (kg/hm2)) and P4 (P2O5, 90 (kg/hm2)) was 39.2%, 105.3%, 73.0% higher than that of the treatment with P1 (P2O5 0 (kg/hm2)) under W3 (50% seawater) irrigation respectively. 2) Phosphorus fertilizer could enhance absorption of K+, Ca2+ and Mg2+, especially the selectivity ratio of SK,Na (root/stem) and SK,Na (root/leaf) and decline the absorption of Na2 and Cl-. And the effect increased significantly with the augments of seawater concentrations up to 75% seawater. The contents of K+, Ca2+ and Mg2+ were higher in leaves than in stems and in roots, while the contents of Na+ and Cl- were higher in roots than in stems and leaves. The selectivity ratio, SK,Na (root/leaf), in the treatment of P3 (P2O5 60 (kg/hm2)) was, respectively, 52.7%, 65.8%, 68.5% and 68.9% higher than in control ( P2O5 0 (kg/hm2), P1) under irrigation with W1 (fresh water), W2 (25% seawater), W3 (50% seawater) and W4 (75% seawater). 3) Phosphate fertilizer significantly increased N content in roots of girasole (Helianthus tuberosus). For example, the N contents in roots in the treatment of P3 (P2O5 60 (kg/hm2)) was 0.43%, 0.64%, 0.64%, 0.51% higher than in control (P2O5, 0 (kg/hm2), P1) under irrigation with W1(fresh water), W2 (25% seawater), W3 (50% seawater) and W4 (75% seawater), respectively.