Utilization of applied fertilizer nitrogen and irrigation water by drip-fertigated squash as determined by nuclear and traditional techniques

Field experiments were conducted to evaluate utilization of applied nitrogen (N) and irrigation water to squash in response to method of fertilizer application and rates of fertigation N. The following treatments were studied in a randomized complete block design with four replications: zero N (N0), 50 (N1), 100 (N2) and 150 (N3) mg N L-1 in the irrigation water (IW). Additional soil application treatment (NS) equivalent to N2 was included. The fertilizers were either injected into IW by means of an injection pump for the fertigation treatments or applied directly to the soil followed by irrigation for the soil application treatment. Squash was planted in plots with four rows per plot. Each plant row had its own irrigation line and each plant its own dripper. Irrigation was applied to replenish 80% of the Class A pan evaporation twice a week. Neutron probe readings were taken before and after each irrigation at 15, 30, 45, 60 and 90 cm soil depth. 15N labeled fertilizers were applied to microplots which contained four plants within each plot. At harvest, plant samples were taken from the microplots for the 15N measurements and from the mainplot for yield determination and chemical analysis. Nitrogen uptake and % of N derived from fertilizers (%Ndff) increased with fertigation compared to soil application treatment. N uptake dff had a similar trend as the Ndff. Fertilizer N utilization efficiency (FNUE) by fruits as determined 15N was lower with the soil application than with fertigation treatments and tends to decrease with increasing N fertigation rates. FNUE values calculated by the difference method were higher than those determined by 15N data. All components of FNUE except the recovery efficiency decreased with the soil application method and with increasing fertigation N rates. FNUE correlated positively with squash yield in both seasons but was stronger in the second season. Water consumption increased with increasing N rates. Water use efficiency increased with N application and was higher with fertigation treatment. Water depletion was maximum in the 30 cm topsoil, suggesting the depth of maximum roots growth. It was concluded that yield, FNUE and WUE increased with N fertigation compared to soil application. The difference method tends to give higher FNUE values under relatively less favorable climatic conditions compared to those measured by 15N data. Overall, the results indicate that fertigation is a more efficient technique for fertilizer application to squash.