IMPACT OF ORGANIC AND INORGANIC NITROGEN FERTILIZERS ON WASHINGTON NAVEL ORANGE TREES. I. VEGETATIVE GROWTH, YIELD AND SOIL PROPERTIES

Abstract

Poultry manure has a salutary effect on soil fertility, increase plant nutrients and improving the soil conditions for citrus growth, productivity and ensure economic yield with a good quality.  Therefore, a field experiment was conducted during 2017 and 2018 seasons on 20 year old Washington navel orange trees grown in a private orchard in Kafr El Sheikh Governorate, Egypt. This study aims to evaluating the effect of poultry manure and ammonium sulphate alone or in combination on soil chemical properties, vegetative growth and yield of Washington navel orange trees. The treatments consist of T1 (100% inorganic nitrogen), T2 (66.6% inorganic nitrogen + 33.3% organic nitrogen), T3 (50% inorganic nitrogen + 50% organic nitrogen), T4 (33.3% inorganic nitrogen + 66.6% organic nitrogen) and T5 (100% organic nitrogen). Results indicated that, combined application of organic and inorganic nitrogen fertilizer  especially T4 (203.8 kg/feddan ammonium sulphate + 3.64 ton/feddan poultry manure) and T3 (305.8 kg/feddan ammonium sulphate + 2.73 ton/feddan poultry manure) resulted in significant increase in NH4+ N, NO3- N, organic matter and Zn; and decreased pH, cadmium, lead and electrical conductivity of soil. Moreover, the treatments increased leaf content values of N, P, K, Ca, Fe, Mn and Zn in both seasons. Data also indicated that application of 305.8 kg/feddan ammonium sulphate + 2.73 ton/feddan poultry manure (T3) and application of 203.8 kg/feddan ammonium sulphate + 3.64 ton/feddan poultry manure (T4) gave the highest values of tree size and vegetative growth in terms of shoot number/branch, shoot length, leaves number per shoot and leaf area of Washington navel orange trees compared to mineral nitrogen fertilizers only. As for yield and fruit quality, treatment of T3 (50% inorganic nitrogen + 50% organic nitrogen), T4 (33.3% inorganic nitrogen + 66.6% organic nitrogen) produced the highest yield and improve fruit quality in terms of fruit weight, fruit size and fruit firmness. This treatment also increased SSC%, SSC/acid ratio and vitamin C and reduced acidity, nitrate and nitrite in fruit juice. In general, combined application of 305.8 kg/feddan ammonium sulphate + 2.73 ton/feddan poultry manure (T3) was recommended for improving soil chemical properties and the best growth, yield, fruit quality and nutritional status of Washington navel orange trees.