By SJOERD WILLEM DUIKER
Soils are already dry in many parts of the state and rain is not in the forecast for the coming weeks. Crops are suffering and we wonder what can be done to avoid drought risk in rainfed crop production?
Drought stress is being reported in different parts of the state. What are some key factors to reduce drought stress in crop production?
Key Factors to reduce drought stress
1. Some soils store a lot more moisture than other.
Using soil characterization data, I calculated the plant available water (PAW), which is the water the soil is able to hold between permanent wilting point and field capacity, for each layer in the rootable zone of four typical soils in Pennsylvania. The results are shown here:
| Soil series | Parent material | Key factors | Plant Available water in root zone (inches) | 50% of Plant Available Water in Root Zone (inches) | # Days until drought symptoms in summer |
|---|
| Hagerstown silt loam | Limestone | Deep soil | 6.85 | 3.43 | 17 |
| Opequon silt loam | Limestone | Shallow soil | 2.48 | 1.24 | 6 |
| Andover silt loam | Colluvium | Fragipan at 23" | 2.75 | 1.43 | 7 |
| Berks silt loam | Shale | High rock fragment content, shallow | 1.84 | 0.92 | 5 |
The Hagerstown is a typical deep limestone soil. We assumed roots would grow to 50" depth. The Opequon is a soil that is typical of rock outcroppings in limestone country – in this case rooting depth was only 17". The Andover is a poorly drained soil with a seasonally high water table due to presence of a fragipan, limiting rooting depth. These soils are common on the sides of the mountains in the Ridge and Valley Region, and can also be found in western and northern Pennsylvania. Berks soils are well-drained soils developed from shale. They are very droughty because of high rock fragment content. Typically, crops will start showing drought symptoms when PAW is 50% depleted. Assuming 1.4 inches of water use per week (typical of a corn crop in July), the stark differences between soils now becomes very evident, because on a deep limestone soil it may take 17 days of no precipitation before drought symptoms appear while on the other soils it takes less than a week! Key message is that especially on the droughty soils it becomes crucial to use drought-mitigating strategies.
2. Diversity in the crop rotation
Drought risk can be spread out by growing a diversity of crops on the farm. The peak of moisture demand of corn (about 1.4 in/wk) is in July and early August when it needs about 1.4 inches per week, while that of small grains like wheat (about 1.7 in/wk) falls in June. Because temperatures tend to be higher in July/August, drought risk is greater in corn than in small grains. Further, corn is highly sensitive to drought at silking increasing yield reduction risks due to drought. Growing corn after deep-rooted crops like alfalfa results in deeper rooted corn also – this is one of the main reasons for higher corn yields in rotations with perennial forages. Some farmers have stopped growing corn on droughty soils and moved to more drought-resistant crops like forage sorghum or sorghum-sudangrass.
3. Plant early
It is crucial to develop a deep root system before summer droughts hit your farm. Late planted corn is much more sensitive to drought than early planted corn because of a smaller root system at the beginning of July.
4. Grow cover crops for grazing or forage instead of double-cropped soybeans
In a study comparing grazing of cover crops after small grains we found that grazing cover crops can be more profitable than double-cropped soybeans, especially on drought soils.
5. Reduce runoff and evaporation losses by leaving mulch cover
Crusting and sealing are common phenomena on exposed soil, and runoff can be greatly reduced by keeping soil covered with crop residue. On top of that, the residue conserves moisture by reducing water evaporation from the soil surface. In a study in Eastern Ohio, 16% of annual precipitation was lost due to runoff in conventional tillage, while it was virtually nil in continuous no-till that had high crop residue cover.
6. Improve soil health
Roots don't develop well when soil is compacted. It becomes therefore very important to avoid soil compaction to reduce drought risk. Improve soil organic matter content by using liquid dairy or packed manure, leaving crop residue in the field instead of removing it, and avoid disturbing the soil with tillage. Use cover crops after main crop harvest to improve soil properties. Stimulate deep burrowing earthworms by leaving crop residue cover and avoiding soil tillage. These practices help improve the water holding capacity of the soil and improve porosity so water can easily infiltrate and percolate to deeper layers. The residue helps reduce runoff and evaporation.
Source : psu.edu