Interaction between P Fertilizer and Sewage Sludge on Availability and Fractions of P and maize (Zea Mays L.) Indices in a Calcareous Soil

The deficiency of available phosphorus (P) is considered as a main problem in Iran’s soils. In order to increase the available P, chemical fertilizers are used. However, P in chemical fertilizers are transformed into less available forms over time. To improve the efficiency of P fertilizers, organic amendments could be effective. Sewage sludge contains an abundance of organic matter and nutrients and is used to improve the productivity of farmland and enhance yield. This study conducted to investigate the effect of the interaction of sewage sludge and P fertilizers on availability and mineral of P and maize (Zea Mays L.) indices in a calcareous soil.

This study was conducted based on factorial experiment in a completely randomized design with 3 replications. The experimental factors were chemical fertilizer (0 and 50 mg/kg of KH2PO4) and sewage sludge (0 and 1 % w/w). The treated soils were kept in 80% of the field capacity in greenhouse condition for one month. The maize (single cross 704) was planted in 3 kg pots under greenhouse of Shahrekord University. After 2 months planting, shoot was removed and maize indices (P concentration, dry matter, and uptake) were determined. Also, after planting, soil sampled from pots and the various fractions of P including (soluble P, Fe-Al bonded P, Ca bonded P, residual P, and organic P) and available (P Olsen and CaCl2 0.01 M methods) were determined.

The results showed that interaction between P fertilizer and sewage sludge on P extracted by Olsen method wasnot significant (p>0.05), while in P extracted by CaCl2 0.01 M was significant (p<0.05). The results revealed that by addition the 50 mg/kg P, P-Olsen and P-CaCl2 increased 21.4 and 60%, respectively, while 1% sewage sludge application P extracted by Olsen and CaCl2 0.01 M methods increased 83.2 and 200%, respectively. The effect sewage sludge (except residual P) and chemical fertilizers on all P fractions were significant (p<0.01). In addition, the interaction between chemical fertilizer and sewage sludge was only significant on Ca -bound P (p <0.05). The effect of sewage sludge on P fractions was more remarkable than chemical fertilizer and their interaction effect. By addition 50 mg/kg P fertilizer, P concentration in maize and the dry matter increased 8.2 and 25.9%, respectively. Similarly, in comparison with without sewage sludge, by sewage sludge application these indices increased 4.9 and 194%, respectively. The interaction of sewage sludge and P fertilizers was significant on maize uptake (p<0.05). The P uptake increased 32.5% in sewage sludge + 50 mg/kg P fertilizer compared to 1% sewage sludge and increased 170 % compared to 50 mg/kg P fertilizer.

The results showed that the effect of chemical P fertilizer application on extracted P by Olsen method wasn’t related to sewage sludge application. In treated soil with sewage sludge, available P considerably increased compared to treated soils with P fertilizer that could be attributed to different impact of treatments on P fractions. Also, the effect of chemical fertilizer application on uptake of P was related to sewage sludge rates.