Residual effects of potassium placement for conservation-till corn on subsequent no-till soybean

Biannual surface application of potassium (K) fertilizer prior to corn (Zea mays L.) in a corn–soybean (Glycine max (L.) Merr.) rotation has been common in conventional-till crop production in North America; however, whether this traditional K management practice is effective for soybean when both corn and soybean are grown with conservation tillage is largely unknown. This study evaluated the residual effects of spring K fertilizer placement in conservation tillage systems applied to previous corn on subsequent no-till soybean. Experiments involving a corn–soybean rotation were conducted from 1997 to 2000 on a silt loam soil (Albic Luvisol) with 12 years of continuous no-till management near Paris, Ontario, Canada. The fields had low initial soil-test K levels (<61 mg l−1) and evident soil K stratification in the top 20 cm. In the “corn” years from 1997 through 1999, spring K fertilizer placement methods of deep band (76 cm centers), surface broadcast, broadcast plus shallow band, and no K were evaluated for no-till, spring zone-till, and spring mulch-till tillage systems (1997 and 1998) but for no-till alone in 1999. From 1998 to 2000, soybean was no-till planted in 19 cm row widths on the respective previous-year corn treatments without further K fertilizer application. Soybean leaf K concentrations responded more frequently and positively to K application in no-till corn than in zone-till and mulch-till corn. Deep band and surface broadcast K placements were similar in their residual effects on soybean leaf K. Positive soybean yield responses to residual K fertilizer were observed in only 1 out of 3 years despite consistent increases in both soil K and soybean leaf K concentrations where K was applied to previous corn. On long-term no-till fields with low soil K levels, interrupting a continuous no-till corn–soybean system with mulch-till corn production provided residual benefits in soil K availability and leaf K nutrition for subsequent no-till soybean. Furthermore, the residual effects of K fertilizer applied to previous corn on subsequent no-till soybean were not affected by K placement method.