Crop Yield and Soil Phosphorus as Affected by Liquid Swine Manure Phosphorus Application Using Variable-Rate Technology

摘要

Soil-test P (SIP) and crop P needs vary within fields and variable-rate technology can be used to apply P more effectively. The objective of this study was to evaluate within a corn (Zea mays L.)-soybean [Glycine max (L.) Mem] rotation grain yield and SIP response to fixed-rate (FR) and variable-rate (VR) liquid swine (Sus scrota domesticus) manure P application using strip-trials, global positioning systems (GPS), yield monitors, and geographical information systems (GIS). Treatments replicated four or five times were a control and manure P applied with FR or VR once before soybean of two rotation cycles in one field and three cycles in another. Strip width and length were 18.3 m and 605 to 660 m, respectively. Initial soil samples were taken from 0.3-ha cells and post-harvest samples were taken each year by treatment (0.1-ha cells). High N (for corn) and K rates were applied uniformly across all strips. Manure P increased strip-average grain yield (P <= 0.05) in eight of nine site-years but yield for FR and VR did not differ. The study of yield responses for field areas with different SIP showed that manure P always increased yield with SIP very low or low (<16 mg Bray-P-1 kg(-1)) and only in three site-years with STP optimum (16-20 mg P kg(-1)). Yield responses differed between FR and VR in very low areas of one site-year, where VR increased corn yield more than FR. The VR method reduced within-field SIP variability compared with FR with the exception of only one site-year. Although VR did not increase yield compared with FR, less manure P was applied to high-testing areas and it reduced SIP variability.