A quick review of subsoil moisture during the fall of 1999 and the spring of 2000 shows that subsoil moisture did not recharge much from October 30, 1999 to April 10 of 2000 (table 1). The five subsoil moisture sites gained from 0.6 to 4.2 inches of moisture during the late fall and early spring. The locations near Newell and Schaller only gained 0.6 and 2.4 inches of subsoil moisture.
Table 2 shows the April 11 to September 1 rainfall was almost normal in Milford, Estherville, Spencer and Pocahontas. However, rainfall at the Sac City and Storm Lake weather reporting stations was 8.4 and 9.5 inches below normal, respectively.
Therefore, this lack of subsoil moisture and summer rainfall impacted county corn grain yields. Corn grain yields as reported by USDA NASS were in the 150 bu/a range for several northwest Iowa counties. However, corn yields for Buena Vista and Sac counties were 136 and 128 bu/a, respectively (table 3).
This information shows that continued dry weather in the spring and summer of 2021 could impact corn and soybean grain yields. Subsoil moisture levels that are not replenished by early summer make corn and soybean crops become more dependent on summer rainfall. Summer rainfall in the year 2000 supplied the needed moisture for normal corn and soybean yields in Dickinson, Emmet, Clay, and Pocahontas counties – but not in Buena Vista and Sac counties.
Table 1. Subsoil moisture from fall 1999 and the spring of 2000.
October spring April
30, county 10, moisture
County site 1999 crop 1999 average 2000 gain
-------inches, plant available moisture---------
Dickinson Spirit Lake soybean 1.8 7.8 4.1 2.3
Emmet Estherville corn 5.5 7.9 6.6 1.1
Clay Rossie soybean 4.3 7.5 8.5 4.2
Buena Vista Newell corn 3.7 7.5 4.3 0.6
Pocahontas Rolfe corn 2.0 7.6 3.9 1.9
Sac Schaller. soybean 2.3 7.7 4.7 2.4.
Table 2. Rainfall from April 10 to September 1, 2000.
Actual normal difference
------------------ inches ------------------
Milford 17.0 17.7 -0.7
Estherville 18.6 17.8 +0.8
Spencer 14.7 17.8 -3.1
Storm Lake 10.4 19.9 -9.5
Pocahontas 18.1 19.1 -1.0
Sac City 10.8 19.2 -8.4
Table 3. County USDA NASS corn, soybean grain yields, 2000.
County ----bu/a----
Dickinson 151 46
Emmet 156 43
Clay 153 49
Buena Vista 136 38
Pocahontas 156 43
Sac 128. 34
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