Long-term N fertilization reduces uptake of N from fertilizer and increases the uptake of N from soil.

Long-term supply of synthetic nitrogen (N) has the potential to affect the soil N processes. This study aimed to (i) establish N response curves to find the best balance between inputs and outputs of N over four ratoons; (ii) use 15N-labeled fertilizer to estimate the N recovery efficiency of fertilizer applied in the current season as affected by the N management in the previous three years. Nitrogen rates (control, 60, 120, and 180 kg ha-1 N) were applied annually in the same plots after the 1st, 2nd, 3rd, and 4th sugarcane cycles. Sugarcane yield, N uptake, and N balance were evaluated. In the final season, 100 kg ha-1 of 15N was also applied in the microplots to evaluate the effect of previous N fertilization on N derived from fertilizer (NDF) and N derived from soil (NDS). Sugarcane yields increased linearly with the N rates over the four sugarcane-cycles. The best balance between the input of N through fertilizer and N removal by stalks was 90 kg ha-1 N in both the 1st and 2nd ratoons, and 71 kg ha-1 N in both the 3rd and 4th ratoons. Long-term application of N reduced NDF from 41 to 30 kg ha-1 and increased NDS from 160 to 180 kg ha-1 N. A key finding is that long-term N fertilization has the potential to affect soil N processes by increasing the contribution of soil N and reducing the contribution of N from fertilizer.

X-ray Spectroscopy Fostering the Understanding of Foliar Uptake and Transport of Mn by Soybean (Glycine max L. Merril): Kinetics, Chemical Speciation, and Effects of Glyphosate.

Increasing the yield of soybean is a challenge to humankind dependent on several management practices, such as fertilizing and weed control. While glyphosate contributes to controlling weeds, it can interfere with spray mixture stability and, supposedly, complex with micronutrients within the plant tissue. This study investigated the effects of glyphosate on soybean foliar uptake and transport of Mn supplied as MnSO4, MnHPO3, Mn-ethylenediamine tetraacetic acid (EDTA), and MnCO3. These fertilizers induced ultrastructural changes in the leaf cuticle, regardless of the glyphosate mixture. Except for MnCO3, all tested sources increased the Mn content in the petiole. The mixture of glyphosate impaired Mn transport from MnSO4 and MnHPO3, but no evidence of Mn-glyphosate complexation within the plant was found. Manganese is rather transported in a similar chemical environment regardless of the source, except for Mn-EDTA, which was absorbed and transported in its pristine form. Interferences of glyphosate seem to be related to complexations in the tank mixture rather than affecting nutrients' metabolism.

In Vivo Evaluation of Zn Foliar Uptake and Transport in Soybean Using X-ray Absorption and Fluorescence Spectroscopy.

Understanding the mechanisms of absorption and transport of foliar nutrition is a key step towards the development of advanced fertilization methods. This study employed X-ray fluorescence (XRF) and X-ray absorption near edge spectroscopy (XANES) to trace the in vivo absorption and transport of ZnO and ZnSO4(aq) to soybean leaves (Glycine max). XRF maps monitored over 48 h showed a shape change of the dried ZnSO4(aq) droplet, indicating Zn2+ absorption. Conversely, these maps did not show short movement of Zn from ZnO. XRF measurements on petioles of leaves that received Zn2+ treatments clarified that the Zn absorption and transport in the form of ZnSO4(aq) was faster that of ZnO. Solubility was the major factor driving ZnSO4(aq) absorption. XANES speciation showed that in planta Zn is transported coordinated with organic acids. Because plants demand Zn during their entire lifecycle, the utilization of sources with different solubilities can increase Zn use efficiency.

Agronomic efficiency of NBPT as a urease inhibitor: A review.

Urea is the most widely used nitrogen (N) fertilizer, with a projected increase in annual demand of 1.5% in the coming years. After its application to soil, urea undergoes hydrolysis via the urease enzyme, causing increases in the soil pH in the surrounding area of the granules and resulting in NH3 losses that average 16% of N applied worldwide and can reach 40% or more in hot and humid conditions. The use of urease inhibitors is an effective way to reduce NH3 losses. Several compounds act as urease inhibitors, but only N-(n-butyl) thiophosphoric triamide (NBPT) has been used worldwide, being the most successful in a market that has grown 16% per year in the past 10 years. Only in the past three years other compounds are being commercially launched. In comparison to urea, NBPT-treated urea reduces NH3 loss by around 53%. Yield gain by NBPT usage is of the order of 6.0% and varies from -0.8 to 10.2% depending on crop species. Nitrification inhibitors usually increase NH3 volatilization and mixing them with urease inhibitors partially offsets the benefits of the latter in reducing NH3 loss. The efficacy of NBPT to reduce NH3 loss is well documented, but there is a need for further improvement to increase the period of inhibition and the shelf life of NBPT-treated urea.