http://vasat.icrisat.ac.in/?q=node/188 

Groundnut pod development takes place in the soil making it difficult to correctly judge the maturity of the crop. It is god to have considerable experience and great vigilance to carry out the harvesting operations efficiently without much loss of quality and yields.A proper time to commence the harvest is when a good number of pods are fully developed and are fairly intact.Maturity of pods is normally achieved when the vine begins to turn yellow and leaf shedding starts.

                                              Groundnut plant ready for harvest

The actual maturity of the pod is determined when they attain normal size with prominent veins, the inside of the shell turns dark and the kernels reach maximum growth accompanied by good coloration of the seed coat.
A fully mature pod can often be difficult to split open with the pressure of the fingers.
An immature pod can be split easily revealing the white inside surface of the pod which appears also to be spongy in texture.
These criteria may help in assessing the correct stage of the harvest of groundnut crop.
Delay in maturation may occur because of late-season drought stress.
Long periods of rain immediately prior to harvest may result in both yield loss and deterioration of quality of groundnuts.
Harvesting at the proper time ensures that a high percentage of mature pods remain on the plants and the maximum number of pods has attained their greatest weight.
Following are the tips for maturity testing:

• Select five to ten plants from representative areas of the field.

• Pull out all pods from the plants.

• Break open each pod to examine internal hull and seed coat color to identify maturity of the pods. Separate mature pods from immature pods.

• Count the number of mature and immature pods.

Following are the tips for maturity testing:

•  Calculate the percentage of mature pods i.e.

% mature pods =  (mature pods X 100) / (mature + immature pods)

•   To harvest, the percentage of mature pods need to be:

Bunch type:   75 to 80 percent                    Runner type:  70 to 80 percent
Other considerations for harvesting:

• If leaf spot or other diseases are problem in the field, do not delay harvest.

• If there is a weather forecast that would delay the harvest, this must be taken into account.

• Harvesting must be done when sufficient labor and adequate equipment are available.

• Failure of peg strength and well-filled pods with pink seed coat indicate maturity in large-seeded Virginia type.

• Signs of weakening peg strength indicate immediate need for harvest if excessive losses are to be avoided.

• Check groundnut crop closely as the average number of days to maturity approaches.

 Hand pulling of groundnut plants 

Harvesting usually consists of a series of operations comprising digging, lifting, windrowing, stocking and threshing. Among the field operations concerned with groundnut cultivation, harvesting is the most laborious and costly endeavor.

The actual method of harvest employed depends upon the type of groundnut grown. In bunch types, pod development is confined to the base of the plant and the pegs carrying the pods into the soil are thick and strong. Almost all the pods are recovered with the plants when they are pulled out of the soil. The bunch type of groundnut is mostly harvested by pulling out the plants with manual labor in India (Fig.). Usually 12 to 14 laborers can harvest one-hectare area of groundnut crop in one day.

                   Bunch type of groundnut                                                      Hand pulling of groundnut

The spreading or semi -spreading (Fig.) groundnut types produce pods all along the running stem. This type of groundnut is harvested either manually or by using a blade harrow (Fig.) or even a country plough. The soil should be sufficiently moist for easy harvesting and without loosing pods in the soil.

                                                                                                         Harvesting groundnut using blade harrow 

Harvesting may sometimes become a problem especially when the crop has passed the stage of full maturity and the soil has hardened. In this case, it is customary to lift the plants by loosening the soil either by working a hand hoe, a plough or a blade harrow along the plant rows. If after lifting the crop manually it is observed that a good percentage of the pods have been left in the soil, the same implements may be used to pick the leftover pods. In certain areas, the vines are uprooted with country ploughs and the vines and pods are picked by manual labor. The pods left over in the soil are picked by hand. Groundnut diggers drawn by a pair of bullocks or by tractor are available in market. The bullock-drawn groundnut digger can harvest groundnut crops over an area of 0.75 ha in 8 hours. Some farmers use conventional 76 inches blades attached to cultivator frame to dig groundnut.
The harvested plants are kept in the field for drying and curing. Because of common usage, the terms curing and drying are often used interchangeably. Curing is the process of water removal such that the basic flavor quality of groundnut is optimum after harvest.

                        Drying groundnut in the field

Extremely high temperatures, while the harvested crop is in the field, can promote far too rapid drying and may contribute to the development of off-flavors. After proper curing and drying, the pods are separated from the plants.
This operation is called stripping.Stripping of pods is performed manually by the small farmers. Also groundnuts meant for seed purpose are stripped manually (Fig.).

                        Stripping of pods manually                                                       Stripping of pods with a stripper

Large quantities of bunch type of groundnuts can be stripped using groundnut strippers. In some areas in India the plants are first lifted out of the soil, dried in the field and then the pod ends of the plant are knocked against a crossbar to dislodge the pods. In this process some pods will be damaged though this method of stripping is cheaper.

In the case of runner types, the plants are first allowed to dry, then are beaten with flails and the pods are separated from the beaten mass by winnowing. The pods left over on the vines are handpicked. This method of stripping is not preferred as it is considered to reduce the fodder value of the vines. When groundnuts are harvested they contain wide range of foreign material like dust, rock pieces, sticks/ previous crop residues, immature pods, pops, leaves, stems and hulls etc. This impacts quality, beginning with airflow restrictions and uneven moisture distribution during curing. Foreign material at 5 percent and above brings down the value of groundnut brought to market. Hence, proper cleaning of the pods from the foreign material will fetch a better price to the produce.