Japanese (Forage) radish, a crop that is taking root

By Delia Thomson, Agronomist, PANNAR SEED
Contact details: delia.thomson[at]pannar.co.za of 060 970 0717

Japanese radish (Raphanus sativus), from the Brassicaceae (or Cruciferae) family, has become a well-known and utilized autumn or winter crop in the cooler, cropping areas in the country. Japanese radish is used widely both in pure stands or in mixed pasture systems. Planting times do vary across the country with some cool areas able to plant as early as mid-December. For most areas, with relatively reliable rain the recommended planting window is from January until early March. Seeding rates are between 2 – 3.5kg/ha in rows. If planted too early there is a risk that the seedlings could be damaged by hot weather as well as plants switching into reproductive phase and flowering early. However, keep in mind that it is normal for a percentage of Japanese radishes to flower earlier and change to seed formation. Insects can damage seedlings, be on the lookout for them and apply the necessary spray. Conversely if planted dryland too late the risk of missing the last rains and having lower soil moisture content resulting in lower yields is higher.

Above: Thomas Fortmann, near Estcourt, with a very nice plant of Endurance Japanese Radish. This cool season crop can produce a huge amount of feed.

Japanese radish is a crop that is gaining popularity due to its many advantages some more well-known and obvious than others. Firstly, are the advantages associated with its properties as a forage. It fits in well with mixed farming operations and makes an excellent rotation crop with maize and soy. It has an established and well-known cold and drought tolerance making it a popular choice in filling fodder flow gaps over autumn and winter. These are winter hardy plants; however, it must be noted that leaf injury and deterioration can occur at temperatures less than 0 °C. Japanese radish can bulk up a large amount of forage per hectare. The production potential can vary dramatically depending on time of planting, soil potential and rainfall. Under irrigation and high potential soils 14 ton/DM/ha can be achieved. Under dryland conditions tonnage ranges between 4 - 10 ton/DM/ha depending on parameters mentioned (see table 1). The stocking rate on Japanese radish is outstanding for a winter crop, with 6 ton/DM able to carry 50 small stock units for 120 days (see table 1).

Table 2 shows yield results of trials carried out at Cedara for both Endurance and Nooitgedacht (both available in PANNAR’s product package), at different harvest dates through the season. The variety, Endurance, is the result of a long and intensive breeding program run at Cedara, between the ARC-API Cedara and PGW New Zealand. The aim of this breeding program was to produce a high yielding, late-flowering fodder radish variety. The data collected over the years showed Endurance achieving the objectives set. The most notable difference with Endurance is its late flowering trait as compared to other varieties in the market. In addition to these attributes Endurance also has soft relatively hairless leaves and moderate to good resistance to rust infection. PANNAR has the exclusive marketing rights to Endurance in Southern Africa.

There can be some misunderstanding on the feed value of Japanese radish with many still believing that the; “nutritional value is all in the leaves and the tubers are just water”. This is a half-truth, it is true that the tubers do have a high-water content of about 90%, however, on a dry matter (DM) basis they are easily digestible and energy rich. Crude protein values in the roots vary from 18-20% and 20-30% in the leaves. The combination of the energy in the roots and the protein in the leaves make it excellent for animal production. It is important to note that if utilized in late winter and the leaves have deteriorated or been grazed before (lowering the protein levels) protein supplementation maybe necessary.
Utilization of Japanese radish is either by grazing or lifted and fed out. Lifting and feeding out does result in less loss and can increase yield fed out by about 30%. Sheep performance has been shown (trials done in Ermelo) to improve when grazed rather than pulled and fed out, however they do utilize pulled radish, thus in times of forage shortage it would maximize forage fed out. Chopping radish once lifted is not recommended as it can become a choking hazard in cattle. In grazing systems, strip grazing does result in the best utilization with less wastage and trampling when compared to open grazing. Timing of Japanese radish utilization is advantageous in that it can be utilized as it is ready or left as a bulk forage store for later in the winter. This adaptability sets it above some other winter crops as well as filling the mid-winter forage gap in cold areas. If the plants begin to flower the tuber quality deteriorates and becomes pithy.
Being a member of the brassica family there are management factors to be aware of when utilizing it. A few to consider are: introduction of livestock to the pasture slowly; do not put hungry animals on to a brassica pasture especially if unaccustomed to it; ensure livestock have access to hay or grass pasture (interseeding with forage cereal grain is an option); it is important to manage the nitrogen in the system and fertilize according to the recommendations. Excessive nitrogen can result in nitrate build up in the leaves and cause nitrate poisoning. Although there are management factors to consider when growing a crop from the Brassicaceae family, Japanese radish is a product that will fill the gap in cool season fodder flows with good yields and quality forage.

Japanese radish in a crop rotation also have soil conservation and health benefits. Before utilization the large tap root and foliage help protect the soil against erosion. The large tap root of radishes allows these crops to penetrate and break up shallow layers of compacted soils or plough pans. This is where the common nickname of “biodrills” comes from. This action promotes increased infiltration of water into the soil profile and promotes deeper rooting in subsequent crops. Research (Maryland) found four times as many corn roots penetrated compacted subsoil after a forage radish cover crop than after leaving it fallow. If planted early enough (preferably 6 weeks prior to frosts) radish can produce an aggressive growth habit that will spread out and canopy which outcompetes autumn and winter weeds. This foliage also helps with the infiltration of any late rainfall into the soil. If unutilized and left to decay in field, water infiltration and surface drainage improves due to channels left by the large decaying roots.

Over the past few seasons, with lower rainfall levels across the country Japanese radish’s lower water requirements and ability to produce high yields and quality forage compared to other winter crops has increased its popularity and it is indeed taking root. Endurance with its later flowering, smoother leaves and good rust tolerance is adding significantly to the already long list of advantages of growing this crop. If you are interested in trying some in your production system give your nearest PANNAR territory representative a call.