Effect of Tillage Systems on Proso Millet Production

Proso millet (Panicum miliaceum L.) is well-adapted for the Central Great Plains and could be planted in a winter wheat (Triticum aestivum L.)-millet-fallow rotation, resulting in two crops in 3 yr. To determine the most suitable tillage system for proso millet production within this rotation, seven tillage management systems were evaluated over a 6-yr period (1972-1977). The research was conducted on a mesic Pachic Arguistill soil on the Central Great Plains Research Station near Akron, CO. Comparisons included fall vs. spring tillage and replacing a tillage operation with herbicides. Controlling fall weed growth by tillage alone or with atrazine (2-chloro4-ethylamino-6-isopropylamino-5-triazine) increased grain yield of proso millet and protein content of the grain more than spring tillage for weed control. Increased millet production from fall tillage was attributed to increased soil NOj~-N levels and increased soil water use by millet. Water use efficiency by millet was also increased with fall tillage. Adding N fertilizer decreased millet grain production. Additional index words: Panicum miliaceum L., Nitrogen, Atrazine, Water use efficiency, Grain protein. T DEVELOPMENT of more efficient cultural practices for storing soil water during fallow periods would increase the potential of producers to grow two crops in 3 yr in the Central Great Plains, rather than one crop in 2 yr. One possible two-crop in 3-yr scheme could be proso millet (Panicum miliaceum L.) planted after winter wheat (Triticum aestivum L.), resulting in a wheat-millet-fallow rotation. Proso millet is welladapted for the Great Plains, being a short-season crop with a low water requirement (Briggs and Shantz, 1913). Maximum water demand during the growing season for proso millet in the Central Great Plains is 300 to 350 mm compared with 500 to 550 mm for corn (Zea mays L.) or grain sorghum (Sorghum bicolor L. Moench) (Greb, 1979). Management systems in wheat-fallow rotations affect soil water and NO^-N levels. Wicks and Smika (1973) reported that half of the total weed growth in 1 Contribution from the USDA-ARS, Mountain States Area. Received 25 Nov. 1985. Research agronomist, USDA, Assistant professor of Agronomy, Colorado State Univ., and soil scientist (deceased), USDA, Akron, CO 80720. Published in Agron. J. 78:589-592 (1986). a tillage system for fallow occurred in the fall after wheat harvest. The fall weed growth can use up to 76 mm of stored soil water (Good and Smika, 1978). Thus, control of fall weeds would increase soil water storage. Greb and Zimdahl (1980) reported that decreased tillage during the fallow season increased soil NOf-N levels (weeds being controlled by herbicides). Greb et al. (1974) reported that uncontrolled fall weed growth can consume up to 36 kg/ha of available N. Fallow programs, in which fall weed growth was controlled, increased the protein content of winter wheat grain. Researchers have evaluated spring tillage systems for proso millet production. Nelson and Fenster (1983) compared four methods of preparing a seedbed (burn, plow, stubble mulch, and no-till) in combination with three types of planting on proso millet production. Their results indicated that neither the seedbed nor planter influenced proso millet grain yield. Fertilizer requirements within different tillage systems for proso millet have not been determined. Hinze (1977) speculated that proso millet might respond to N fertilizer if planted into wheat stubble, but not when grown on summer-fallowed land of medium to heavy texture. To determine the optimal proso millet production system, this experiment was conducted (i) to evaluate the effect of tillage systems in wheat stubble on fall weed growth, soil water storage, soil NOj-N level, and proso millet production, and (ii) to determine N fertilizer influence on proso millet production following wheat in different tillage systems. MATERIALS AND METHODS The effects of tillage systems on proso millet production were evaluated in five cropping sequences from 1972 to 1977. The experiment was conducted on a Rago silt loam (fine, montmorillonitic, mesic Pachic Argiustoll) at Akron, CO. The soil contained 13 g/kg organic matter and the pH was 7.4. The experimental design was a randomized complete block with five treatments replicated four times. Plot size was 10 m wide by 24 m long, being established in wheat stubble each year. The treatments evaluated over the duration of the study are shown in Table 1. Tillage system no. 1, spring disking, represents the normal production scheme followed in the Central Great Plains. Disking was performed with a 4-m 590 AGRONOMY JOURNAL, VOL. 78, JULY-AUGUST 1986 tandem disk, while a V-blade was used for sweep plowing. Herbicides were applied at 2.8 X lo4 kg/m2 in 187 L/ha of spray solution with a 4-m boom plot sprayer. The general dates for each cultural operation during the study are shown in Table 1. 'Leonard' proso millet was planted with a deepTable 1. Description of tillage system treatments. Tillage system Cultural operations 1 Spring disk twice (early April and early May), mulch-tread, and plant millet (early June) Spring sweep plow twice (early April and early May), mulch-tread, and plant millet (early June) Fall sweep plow once (July), spring sweep plow (early May), mulchtread, and plant millet (early June) Fall sweep plow twice (July and September), mulch-tread, and plant millet (early June) Fall sweep plow once, atrazine at 0.56 kg/ha (July), mulch-tread, and plant millet (early June) Fall sweep plow once, atrazine at 1.12 kg/ha (July), mulch-tread, and plant millet (early June) Fall sweep plow once, 2,4-D butyl-ester at 2.24 kgiha (July) mulch-tread, and plant millet (early June) 2