Watermelon Response to Soluable and Slow Release Nitrogen Fertilizers

A field experiment with subsurface drip irrigated watermelon was conducted on a Casa Grande s.l. soil at the Maricopa Agricultural Center in 1992 to evaluate the field performance of two slow release nitrogen (SRN) fertilizers in comparison to a conventional soluble N source, urea, ammoniumnitrate (UAN -32). Single, preplant applications of 0, 100 and 200 lbs N /acre supplied from methylene urea (Nutralenes) or 100, 150 and 3(X) lbs N /acre from a methylene urea ammonium sulfate mixture (MUAS) were evaluated in comparison to treatments of UAN -32 containing from 52 to 445 lbs N /acre made in five split applications. Yield response to N rates above 100 lbs/acre were similar for all three N sources, indicating that a single, preplant application of a suitable SRN material at an adequate rate could provide N efficiently over the entire growing season. The highest numerical yield (49.3 tons/acre) was obtained with a N rate of 150 lbs N /acre from the MUAS material. Monitoring of petiole nitrate levels throughout the season indicated that N release from the MUAS was more rapid and more complete than from the methylene -urea product. At suboptimal N rates, i.e. < 150 lbs N /acre, split applications of UAN -32 appeared to be somewhat more efficient than the slow -release products.