What to Do About Empty Peanut Shells? Full Analysis of Causes and Control Measures

Peanuts are a food we eat quite a lot of in our lives. We generally buy ready-made peanuts on the market, and friends who have no contact with farm work rarely know how peanuts grow. Peanuts are highly nutritious and can be pressed for oil to produce peanut oil. So what causes empty peanut shells? What should be done about empty peanut shells? What measures prevent empty peanut shells?

I. What causes empty peanut shells?

1. Variety differences: mainly the large peanut series is prone to the empty shell problem, while the small peanut pearl series rarely is.

Regions of occurrence and soil characteristics: the main regions of occurrence include Jiangxi, Hubei, Jiangsu, Shandong and small parts of Henan and Hebei; the soils include latosols and yellow-brown earths and other acidic or slightly acidic soils, whose content of active calcium is generally low. For example, Wang Minglun of Qingdao Agricultural University found through soil tests on empty-shell peanut fields in the Qixia area of Shandong that the active calcium content was “trace”.

Yield level: at present the per-mu yield level of large peanuts has generally risen from less than 200 kg to more than 300 kg. The empty shell problem, which rarely appeared at low yield levels, is becoming increasingly prominent under high-yield conditions.

Current fertilization situation: in pursuit of yield, most peanut-growing areas apply a lot of nitrogen fertilizer, which is neither conducive to nodule nitrogen fixation nor causes the aboveground stems and leaves to become overly luxuriant; organic fertilizer is allocated very little; and most of the phosphorus fertilizer varieties applied today have changed from the previous superphosphate to diammonium phosphate and ternary high-concentration compound fertilizers. This is very unfavorable for the supplementation of medium and trace elements and nutritional balance in peanut fields.

2. Calcium deficiency in pods can cause empty peanut shells

Peanut is a calcium-loving crop. For every 100 kg of pods produced, about 2.7 kg of calcium is needed. Pod development in particular needs calcium to fill out the kernels and thereby improve plumpness. But peanut is also a crop with limited calcium-absorbing capacity. In the early stage, the growth of aboveground stems and leaves relies on unsubterized young root tips for absorption. Because calcium has very weak transport capacity in the phloem, the large amount of calcium needed by the underground pods after the pegging stage cannot possibly use the calcium absorbed by the root system, and mainly depends on the pegs and young pods themselves absorbing calcium from the soil to meet the need.

Many studies at home and abroad have found that during the pod-setting stage after the pegs grow downward, even if the lower soil layer where the roots are located is not calcium-deficient, the calcium absorbed by the roots is difficult to transport to the pods. When peanut pods form, more than 90% of the calcium must be taken up directly from the surrounding soil by the pegs and young pods. This means that during the more than 70 days from peg entry into the soil to kernel plumpness, as long as severe calcium deficiency or insufficient calcium supply occurs in the soil layer where the pods form, it will directly affect pod formation; in mild cases the kernel outturn rate declines and yield is reduced, and in severe cases it leads to the empty peanut shell problem and total crop failure. As farmers from various places have said in many phone calls, although the aboveground stems and leaves of the peanut are still luxuriant, the harvested pods are often not plump or even empty.

Many years ago, in the acidic soils of southern China, applying lime both neutralized acidity and supplemented calcium, which could reduce the empty peanut shell rate. In the early 1990s, the Henan Academy of Agricultural Sciences applied gypsum to calcareous alluvial soils in the Yellow River flooded area, and the yield increase was also very obvious: generally each kg of gypsum could increase peanut pod yield by 1.6 kg. Early foreign research reports noted that gypsum is a commonly used calcium fertilizer for peanuts in the United States, and direct application at the flowering stage can prevent the empty shell problem.

Other research reports note that the intensity and capacity of calcium absorption differ among different parts of the pod: 15.5% for pegs that have entered the soil, 59.5% for the pericarp of young pods, 7.5% for the kernels of young pods, and 1.5% for the kernels of initially formed pods, showing that the calcium absorption intensity of kernels is the lowest. Moreover, their calcium-absorbing capacity gradually declines with the pod development process. This makes calcium deficiency more likely in the late pod-setting stage, resulting in empty peanut fruits, shriveled fruits, and so on.

II. What should be done about empty peanut shells?

1. Increase Ca fertilizer application. Superphosphate should be mixed with high-quality barnyard manure and composted for 15-20 days before being applied to the soil.

2. Apply potassium fertilizer deeply. Apply K fertilizer below the podding layer to prevent the podding layer from containing too much K, which affects calcium absorption and increases rotten fruits.

3. When plowing, calcium nitrate or calcium chloride can be applied to supplement calcium fertilizer.

4. Increase chemical fertilizer application to reduce the loss of calcium fertilizer in acidic soil environments and increase the activity of calcium fertilizer.

III. What measures prevent empty peanut shells?

1. Increase organic fertilizer application. Because organic fertilizer is comprehensive in nutrients, generally 3000-4000 kg of decomposed organic fertilizer per mu is applied as base fertilizer. If the amount of base fertilizer is large, it can be applied throughout the plow layer; if the amount is small, it can be applied as seed fertilizer.

2. Apply superphosphate. Because superphosphate contains not only phosphorus but also a large amount of gypsum, and gypsum is also called calcium sulfate, it can add calcium fertilizer to the soil. Generally 30-40 kg of superphosphate per mu is applied as base fertilizer.

3. Spray boron fertilizer. Boron is a nutrient element necessary for the normal development of plant flowers and reproductive organs. In sandy soils and soils severely deficient in boron, 1 kg of borax per mu can be applied as base fertilizer or seed fertilizer. In ordinary soils, a 0.2%-0.3% borax solution can be used for foliar topdressing 2-3 times at the early flowering stage.

Spray molybdenum fertilizer. Molybdenum fertilizer can promote well-developed peanut root nodules, dark green leaf color, vigorous growth, and full, plump fruits. At the early flowering stage or the pegging and pod-setting stage, a 0.3%-0.5% ammonium molybdate solution is used for foliar topdressing per mu.

Apply potassium fertilizer deeply. Potassium fertilizer should be applied deeply below the podding layer to prevent the podding layer from containing too much potassium, which affects calcium absorption and increases rotten fruits.

4. If peanut seedlings grow weakly and the leaf color is pale, a 0.3% urea and 0.3% monopotassium phosphate solution can be added, once every 7-10 days, sprayed continuously 2-3 times, which can reduce the empty peanut shell rate and improve the seed-setting rate, generally increasing yield by more than 10%.