Fall Seeded Crucifers for Soil Improvement Before Cucumbers

Crucifer plants produce glucosinolates, which upon cell damage degrade into biologically-active compounds including isothiocyanates. Crucifers have been studied as biofumigants crops for suppression of weeds and phytopathogens. Our previous research found that crucifer cover crops did not consistently suppress weeds and could not replace preemergent herbicides. But forage turnip and oilseed radish may reduce soil compact. The objective was to evaluate crucifers for their ability to reduce weeds, decrease soil compaction, and increase cucumber yields. On September 28, 2009 and August 26, 2010, 15 by 6 m plots were established in a randomized split- block design (crucifer cover crop was the main plot and tillage was the subplot factor) with 4 replications. The crucifer cover crops were: 1) oil seed radish (13.4 kg/ha) [Raphanus sativus var. Oleiferus]; 2) ‘Dwarf Essex’ Rape (6.7 kg/ha) [Brassica napus L.]; 3) ‘Appin’ forage turnip (6.7 kg/ha) [Brassica rapa L.]; 4) ‘Pasja’ Hybrid Forage Turnip (6.7 kg/ha); 5) ‘Nemat’ arugala (9 kg/ha) [Eruca sativa]; 6) ‘Red Giant’ mustard (6.7 kg/ha) [Brassica juncea]; 7) ‘Ida Gold’ mustard (11.2 kg/ha) [Sinapis alba]; and 8) control (no cover crop). On the Cruse Tract Research Farm in Champaign, IL, crucifer seed was has broadcast by hand, and worked in with a culti-packer. Crucifers germinated within 7 days and grew rapidly. Immediately before the first hard freeze, the cover crop in the fall tillage treatment was incorporated with a disk. In the other tillage treatment, the cover crops shoots were allowed to winter-kill. 'Eureka’ cucumbers were transplanted into a single row in the center. The forage turnip and oilseed radish produced more dry biomass than ‘Nemat’ arugula or ‘Red Giant’ mustard. Crucifer cover crop biomass was not correlated with weed suppression in April. The weed communities were dominated by winter annual weeds, especially purslane speedwell. The forage turnip and oilseed radish reduced soil compaction. Cucumber yield in the crucifer cover crop treatments were similar to the weed-free control.