Effects of Subsoiling Frequency and Irrigation Frequency on Delta Corn

Investigators: Jacob Rix, Himmy Lo, Drew Gholson, Lyle Pringle, Dave Spencer, and Gurbir Singh

Date: 2022

Project Summary

Introduction

In historically cotton-growing soils of the Delta, hardpans are prevalent as a consequence of long-term intensive tillage and equipment traffic. These compacted layers restrict root development and water infiltration. To combat this problem, subsoilers have been used to fracture hardpans once every year or longer. The goal is to enhance crop access to soil water and nutrients, thus improving yield on rainfed fields and reducing irrigation frequency on irrigated fields. In previous research on Delta cotton, the combination of annual subsoiling and high-frequency irrigation decreased yield and profit because of excessive soil water. More information is needed on how subsoiling frequency and irrigation frequency jointly affect Delta corn.

Methods

Scientists at NCAAR analyzed the corn portion of a corn-cotton rotation experiment near Tribbett, Mississippi. The soil was classified as silty clay loam, with a hardpan around 8-12 inches below the surface. Replicated across five blocks over five years, each of the 12 treatments in this experiment represented a unique combination of one in-row subsoiling frequency and one furrow irrigation frequency. The four evaluated subsoiling frequencies were no subsoiling (NS), subsoiling only before cotton (CS), subsoiling only before corn (MS), and every-year subsoiling (ES)-all using the low-till parabolic subsoiler in the fall or winter. The three evaluated irrigation frequencies were no irrigation (NI), low-frequency irrigation (LI), and high-frequency irrigation (HI).

Soil water was monitored using a set of Irrometer Watermark 200SS sensors at the depths of 6, 12, 18, and 24 inches in each NS x HI and ES x LI plot. Grain yield was measured using a weigh wagon and was adjusted to a standard moisture content of 15.5%. Profitability was compared assuming corn price of $4.30 per bushel, subsoiling cost of $11 per acre per year, fixed irrigation cost of $44 per acre per year, and variable irrigation cost of $2 per acre-inch.

Results and discussion

Subsoiling before corn increased the infiltration of irrigation water for irrigated corn. More soil water was maintained even with lower irrigation frequency. However, soil water data did not show that subsoiling before corn increased the infiltration of in-season rainfall for irrigated corn. Instead, heavy rains tended to reduce soil water differences between the NS x HI and ES x LI treatments. These findings were exemplified in Figure 1 and were confirmed statistically using pairwise t tests.

At each irrigation frequency, NS and CS were statistically indistinguishable in corn yield just as MS and ES were statistically indistinguishable in corn yield (Figure 2). Without irrigation, subsoiling before corn maximized corn yield. Without subsoiling, high-frequency irrigation maximized corn yield. Low-frequency irrigation and high-frequency irrigation resulted in statistically indistinguishable corn yield only if subsoiling occurred before corn.

Subsoiling before corn and irrigation each increased average profit and decreased profit variability for corn production (Figure 2). The highest average profit was achieved by the MS x LI treatment, whose profit variability was also relatively small. By subsoiling before corn, similar profits could be earned with lower irrigation frequency.

Conclusion

To reap the benefits of subsoiling in Delta corn, subsoiling should be performed every off-season that precedes a corn crop. Subsoiling before corn is strongly recommended for both nonirrigated and irrigated corn in the Delta as an effective practice to preserve farm profits while conserving water resources.

Project Photos

• Topic:
• Cover Crops
• Tillage
• Soil