Evaluating Nitrogen Behavior in Sugarcane after Fertilization Using Leaf and Sap Extract Analyzes

Nitrogen (N) fertilization is important for sugarcane crops, for both agronomic and environmental reasons. Better use of N from fertilizer is required for crop management, and in order to achieve it, adequate N nutrition monitoring is necessary. Sap extract analysis is a sensitive technique that has been adopted in other crops to tackle this objective, and can be used for sugarcane. The aim of this study was to evaluate the behavior of N and the response of sugarcane after N fertilization, using sap and leaf tissue analysis. The study was undertaken in two experimental areas in 2012/2013 season, using ratoon cane, following application of 0, 50, 100, and 150 kg&middotha-1 of N. The youngest visible leaves were sampled from sugarcane at five time points between 0 and 150 days after fertilization, to evaluate the nitrate, ammonium, and total N content of sap extract, and total N content of leaf tissue. At the first sampling point (30 days after N fertilizer application), mineral N in sap increased as a result of N fertilization in medium-textured soil, and remained high until 120 days after fertilization in clayey soil. The total N content of sap followed a similar behavior. Stalk yield was only observed to increase in sugarcane grown in the clayey soil. Sap analysis proved to be an efficient method for monitoring N status in sugarcane grown in different soil types.

Nitrogen fertilization and potassium requirement for cereal crops under a continuous no-till system

Nitrogen(N)and potassium(K)are the most required nutrients for corn and wheat production.Increasing the N application rate usually boosts crop yields.However,many uncertainties remain for K management.Potassium deficiency results in yield losses,but K application rate based on the percentage of K+in the cation exchange capacity(CEC)is doubtful,especially in soil with high CEC.A field trial was conducted to examine the effects of KCl application before sowing corn and wheat,by raising the percentage of K+in CEC at pH 7.0(CECpH7.0)to approximately 2.5%,3.5%,and 4.5%,and adding N as a topdressing(75,150,and 225 kg ha-1 to corn and 40,80,and 120 kg ha-1 to wheat)on the nutrition and yield of corn and wheat under a continuous no-till system(30 years).Exchangeable K+content increased in the topsoil(0–20 cm depth)up to 7.2 mmolc dm-3 after K application at the highest rate,which,however,did not result in significant increases in nutrient uptake and yields for both corn and wheat.The N application rate positively affected the uptake and removal of all macronutrients by corn and wheat.Applying N as a topdressing increased yields of corn and wheat by up to 83%and 22%,respectively.Our results suggest that in the soil with a high CECpH7.0(162.1 mmolc dm-3),the recommendation for K application made by considering the percentage of K+in the CECpH7.0 may result in excessive application of K fertilizer to crops with high K-recycling potential grown under a continuous no-till system.