Corn and soybean planting is progressing very slowly across the state. The starting soil conditions (temperature, water, nitrogen) however are very different from last year. In this blog we’ll benchmark soil conditions using simulated data from the well-calibrated APSIM model.
The 4-inch soil temperature (Figure 1) is below normal across Iowa and much lower than 2021 (up to 20oF lower). Of interest, the 2022 topsoil soil temperatures are approaching record low levels for the first week of May. As a result, the rate of soil N mineralization is below normal in 2022 (Figure 2). Additionally, below normal soil temperatures will slow down the rate of emergence.
Figure 1: 4-inch soil temperature benchmarks. Data are from model simulations, aggregated at crop reporting district.
Figure 2: Soil N mineralization benchmarks. Data are from model simulations, aggregated at crop reporting district.
Soil moisture at 0 to 1.5 feet is above normal for eight of the nine crop reporting districts in Iowa (Figure 3). Northwest Iowa is at normal after a long period of being below normal. In all regions, soil moisture is trending upwards – the opposite direction from May 2021. While it takes a few inches of rain to reverse the current trends, overall, the soil moisture is adequate to support high crop yields and buffer possible droughts later in the season.
Figure 3: 0-1.5 feet soil moisture benchmarks. Data are from model simulations, aggregated at crop reporting district.
The depth to water table has been decreasing from March to early May 2022, except in Northwest Iowa which is stable (Figure 4). As of May 5, the water table depth is near normal in five crop reporting districts, below normal in two crop reporting districts, and above normal in two crop reporting districts. The water table provides an additional buffering capacity to drought as it can supply up to 50% of the crop water needs if the water table depth is near the root zone. Also, the depth to the water table drives water (and nutrient) movement to subsurface tile drainage.
Figure 4: Depth to the water table benchmarks. Data are from model simulations, aggregated at crop reporting district.
Both topsoil moisture and subsoil (water table) moisture are influenced by precipitation inputs and evapotranspiration losses. The building of overall soil moisture over the last two months is because the input exceeds the output. In Central Iowa for example, the precipitation over the last two months is above normal, while temperature and radiation energy is below normal over the last month, which has led to lower evapotranspiration. As a result, soil moisture is increasing.
In summary, the 2022 growing season is starting at very different soil conditions than the last two years. Concerns of low soil moisture availability have been minimized. The next challenge is timely and uniform crop emergence. The forecasted above normal temperatures for next week will help.