Causes of Peanut Empty Shells and Control Measures

A high rate of empty peanut pods directly leads to a significant decline in both yield and quality, resulting in substantial losses for farmers. So, what causes empty peanut pods? What are the underlying reasons, and what preventive and control measures can be taken? Let’s take a look!

I. What causes peanut shells to be empty?
1. The main varietal difference is that the large‑peanut series is prone to empty shells, whereas the small‑peanut Pearl series rarely exhibits this issue.

Geographic Distribution and Soil Characteristics: The primary areas of occurrence include Jiangxi, Hubei, Jiangsu, Shandong, as well as small portions of Henan and Hebei. The soils are acidic or slightly acidic, such as lateritic red soils and yellow-brown soils, and generally exhibit low levels of available calcium; for instance, Wang Minglun of Qingdao Agricultural University found that the available calcium content in the soil of hollow‑shelled peanut fields in Qixia, Shandong, was at a “trace” level.

At present, the yield of large‑seed peanuts has generally increased from less than 200 kg per mu to over 300 kg per mu. Meanwhile, the issue of empty shells—previously rare at low yield levels—has become increasingly pronounced under high‑yield conditions.

The current fertilization practice, driven by the pursuit of yield, sees most peanut-growing regions applying excessive nitrogen fertilizer, which not only impairs rhizobial nitrogen fixation but also leads to overly vigorous vegetative growth. Organic fertilizers are applied sparingly. Moreover, the majority of phosphorus fertilizers now used have shifted from traditional calcium superphosphate to diammonium phosphate and high‑concentration ternary compound fertilizers, a change that is highly detrimental to the replenishment of micronutrients and the maintenance of nutritional balance in peanut fields.

2. Calcium deficiency in pods can lead to empty peanut shells.
Peanuts are a calcium‑requiring crop; for every 100 kg of pods produced, approximately 2.7 kg of calcium is needed. In particular, during pod development, adequate calcium is essential to fill the kernels and enhance kernel fullness. However, peanuts have limited capacity to uptake calcium: in the early growth stage, aboveground stems and leaves rely on the absorption of calcium by young, non‑sclerified root tips. Because calcium exhibits very poor translocation through the phloem, after the peg‑to‑pod stage, the substantial calcium demands of the underground pods cannot be met by root‑absorbed calcium alone; instead, the pods and developing fruits must depend primarily on their own ability to take up soil‑borne calcium.

Numerous domestic and international studies have shown that, during the pod‑setting stage following the penetration of the fruiting peg into the soil, even when the underlying soil is not calcium‑deficient, the calcium absorbed by the roots is often unable to be transported to the developing pods. At the time of pod formation, more than 90% of the calcium required is taken up directly from the surrounding soil by the fruiting pegs and young pods. This means that over the roughly 70 days from peg emergence to full seed filling, any severe calcium deficiency or inadequate calcium supply in the soil layer where the pods develop will directly impair pod formation: in mild cases, this reduces the kernel yield and leads to lower production; in severe cases, it can result in empty pods and total crop failure. As farmers across various regions have repeatedly reported by phone, even though the aboveground stems and leaves remain lush, the harvested pods are often underdeveloped or completely empty.

Many years ago, in the acidic soils of southern China, applying lime not only neutralized soil acidity but also supplied calcium, thereby reducing the incidence of empty peanut pods. In the early 1990s, the Henan Academy of Agricultural Sciences conducted trials on calcareous alluvial soils in the Yellow River floodplain, where gypsum application significantly increased peanut yields—typically by 1.6 kilograms of peanut pods per kilogram of gypsum applied. Early foreign studies reported that gypsum is a commonly used calcium fertilizer for peanuts in the United States, and its direct application during the flowering stage can help prevent the problem of empty pods.

Furthermore, studies have reported that calcium uptake varies among different parts of the pod: 15.5% in the pedicel, 59.5% in the young fruit peel, 7.5% in the young seed, and only 1.5% in the early‑developing seed, indicating that the seed exhibits the lowest calcium‑absorbing capacity. Moreover, this capacity declines progressively as the pod develops, making calcium deficiency more likely during the late pod‑setting stage and leading to issues such as empty pods and shriveled seeds in peanuts.

II. What should be done about empty peanut shells?
1. Increase the application of calcium fertilizer; superphosphate should be mixed with high-quality farmyard manure and composted for 15–20 days before being applied to the soil.
2. Apply potassium fertilizer deeply, placing it below the fruiting layer to prevent excessive potassium in that layer, which can inhibit calcium uptake and increase fruit rot.
3. Calcium nitrate or calcium chloride may be applied to arable land to supply calcium fertilizer.
4. Increase the application of chemical fertilizers to reduce the loss of calcium fertilizer in acidic soils and enhance its availability.
III. What measures can be taken to prevent empty peanut pods?
1. Increase the application of organic fertilizers. Since organic fertilizers provide a well-rounded nutrient profile, apply 3,000–4,000 kg per mu of well-rotted organic fertilizer as a base fertilizer. If the quantity is substantial, it can be incorporated throughout the entire plow layer; if the amount is limited, it may be applied as a seedbed fertilizer.

2. Apply superphosphate. Superphosphate not only contains phosphorus but also a substantial amount of gypsum, which is calcium sulfate and can supply calcium to the soil. Typically, apply 30–40 kilograms per mu as a base fertilizer.

3. Foliar application of boron fertilizer. Boron is an essential nutrient for the normal development of floral organs and reproductive structures in plants. In sandy soils or severely boron-deficient soils, apply 1 kg of borax per mu as a base fertilizer or seed dressing. For typical soils, during the early flowering stage, conduct 2–3 foliar sprays with a 0.2%–0.3% borax solution.

Apply molybdenum fertilizer via foliar spray. Molybdenum fertilizer promotes the development of peanut root nodules, results in dark green foliage, vigorous growth, and well‑filled pods. During the initial flowering stage or the pegging–pod‑setting stage, apply a 0.3%–0.5% ammonium molybdate solution as a foliar topdressing per mu.

Apply potassium fertilizer deeply. Apply it below the fruiting layer to prevent excessive potassium in that layer, which can inhibit calcium uptake and increase the incidence of fruit rot.

4. If peanut seedlings exhibit weak growth and pale foliage, apply a solution of 0.3% urea and 0.3% potassium dihydrogen phosphate every 7–10 days, repeating the spray 2–3 times. This can reduce the rate of empty pods, increase pod set, and typically boost yield by more than 10%.