Impact of Summer Fallow Replacement Crops on Winter Wheat

Impact of Summer Fallow Replacement Crops on Winter Wheat

August 10, 2007

Research Update

In 2004, a study was initiated to determine the relationship of crop grain or forage yield to plant available soil water at planting. The study was conducted on silt loam soils in 2004 and 2005 at Sidney and at Akron, Colo. A range of soil water levels was established with supplemental irrigation prior to planting. Four crops (spring triticale for forage, dry pea for grain, proso millet for grain and foxtail millet for forage) were no-till seeded into corn residue in a split-plot design with four replications per location.

Results of this study indicated that the amount of plant available soil water at planting may be a suitable indicator of yield potential for selected short-season spring-planted crops. The forage crops in the study, spring triticale and foxtail millet, demonstrated a linear relationship of dry matter accumulation to soil water availability at planting. Proso millet also showed potential as a grain crop for use in a flexible summer fallow cropping system based on soil water at planting. Dry pea did not appear to be suited for such a system. Dry pea yields are unstable and sensitive to temperature and water stress near flowering.

The effect of these four summer fallow replacement crops on the subsequent winter wheat crop was evaluated in a continuation of the above study. The results suggest that the amount of soil water available when the summer fallow replacement crop is planted also impacts the subsequent winter wheat crop, although perhaps not to the extent that it affects the summer crop (Table 1). This makes the decision to plant a summer crop or summer fallow prior to winter wheat that much more critical.

The selection of a short-season summer fallow replacement crop may not be as critical as the decision to plant a crop or not, but it still can influence the performance of the subsequent winter wheat crop and the financial return to the farmer. The high cost of dry pea seed, combined with the lack of consistent response of dry pea to soil water at planting, makes dry pea a poor choice for a flexible summer fallow cropping system, despite the agronomic benefits that a legume may provide.

Although it was only observed at Sidney in 2005-2006, it is intuitive that soil water at winter wheat seeding is likely to be greater following early- rather than late-planted summer crops as a result of the increased time between harvest and winter wheat seeding for the former compared to the latter. It is also likely that soil water at wheat seeding would be greater after a forage crop compared to a grain crop as a result of reduced water use over the shorter growing season and subsequent increased time from harvest to wheat seeding. Since increased soil water at winter wheat seeding is usually positively related to winter wheat yield, it would be reasonable, although not always true, that winter wheat yield would be greater after an early-planted forage crop like triticale compared to a late-planted grain crop like proso millet.

Collectively, these studies suggest that a flexible summer fallow cropping system may be feasible for the northern High Plains. Determining a threshold soil water level at which to plant a summer fallow replacement crop will be critical to the success of the system since it will not only influence the performance of the summer crop but also that of the subsequent winter wheat crop.

The flexible summer fallow cropping system appears to be most applicable when using short-duration summer annual forage crops, such as triticale and foxtail millet. Forage yield is more readily estimated by soil water at planting than is grain yield and the shorter duration of forage compared to grain crops tends to leave more soil water for the subsequent winter wheat crop. However, grain crops such as proso millet, with low seed cost and a relatively good grain price, may also be feasible if a grower is willing to accept a greater variability in economic return, i.e., greater risk.

Drew Lyon
Extension Dryland Cropping Systems Specialist
Panhandle REC, Scottsbluff

Table 1. Influence of previous summer crop and its starting soil water level on the grain yield of the subsequent winter wheat crop at Akron, Colo and at Sidney in 2004-2005 and 2005-2006.
 
Akron, CO
Sidney, NE

Treatment

2004

2005

2004

2005

Crop

(bu/ac)

Triticale

10.2

25.6

22.8

28.6

Dry pea

11.0

 

25.3

 

28.3

 

24.7

Foxtail millet

5.6

---

---

33.5

Proso millet

8.9

---

---

33.2

Soil water level

 

 

 

 

Low

4.7

20.4

18.5

27.8

Medium

10.2

23.7

23.1

30.7

High

11.8

32.3

35.1

31.5

— — Contrasts— —

Early vs late***

*

---

---

**

Triticale vs dry pea

NS

NS

NS

NS

Foxtail vs proso

NS

---

---

NS

Low vs high

**

**

**

NS

* and ** indicate a significant difference at the 10% and 5% probability levels; NS indicates no significant difference; --- indicates that summer crop failure prevented these comparisons.

***Triticale and dry pea were planted in early April while foxtail and proso millets were planted in early June.

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