Nutrient Uptake by Grass and Leaching Losses from Soluble and S-Coated Urea and KC1
- S. E. Allen,
- G. L. Terman and
- H. G. Kennedy2
Slow-release fertilizers should provide for more efficient nutrient use by the crop as well as reduce leaching losses. This study was conducted to measure crop response to N or K in uncoated urea, ammonium nitrate (AN), S-coated urea (SCU), KC1, and S-coated KC1 (SCK) and to relate leaching losses to NO3-Nan d cations. In one series, granular N sources to supply 200 or 400 kg of N/surface ha were mixed with the upper 20 cm of a 1:1 mixture of Norfolk s1 (Typic Paleudult) and builders sand contained in 15- ✕ 120-cm columns. A second series was similarly Fertilized with K sources to supply 100 or 200 kg of K/surface ha.
Soil columns were left fallow or planted to tall fescue (Festuca arundinacea Shreb. ‘Kentucky 31’) which was harvested six times at 4-week intervals. Following the sixth harvest of fescue, stubble and roots were incorporated into the soil along with a second application of N or K and cultures were planted to sorghum-sudangrass (Sorghum bicolor ✕ Moench Sorghum vulgare sudanense ‘Green M’), which was harevsted four times at 4-week intervals. Water was applied as required for crop growth and once during each growth period all columns (including fallow) were heavily watered to collect liters (10 cm) of leachate from each.
Total recovery of N by both crops was in the order: SCU-12 > split-AN > SCU-20 > urea > AN > no N. With cropping, 0 to 11% of applied N was found in drainage water. Under fallow, losses of N were much higher (29 to 72%) and were in the order: split-AN > SCU-12 = SCU-20 > AN = urea > no N. These results support the premise that slow-release fertilizers supply more N for crop response, but may not reduce leaching losses. leaching of cations was well correlated with loss of NO3-N (r = 0.83 to 0.90) under fallow, but was less correlated (r = 0.33 to 0.74) under grass.
Recovery of K by both crops was near 100%. Applied K decreased loss of NO3-N, Ca, and Mg under cropping and increased losses under fallow. Leaching of NO3-N and cations was highly correlated. Applied N and oxidation of S in S-coated products both contributed to acidification of the soil, which intensified leaching of Ca and Mg.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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