Soil Health

Eragrostis for Soil Health and Dry Matter Production

By | CONSERVATION AGRICULTURE, Nitrogen, Soil Health | No Comments

In recent years late spring rains and prevailing drought conditions have put many livestock farmers under severe pressure, especially those who have relied on post-harvest crop residues in combination with natural grassland (veld) to carry their stock. Reductions in maize planting and additional losses in dry matter from veld due to drought conditions have resulted significant deficits in fodder flows. In the light of the above, consideration should be given to the establishment of permanent pastures on marginal lands.  This would serve several purposes, including the conservation of the top soil by ensuring permanent ground cover, and also provide a source of early grazing in spring with the additional potential to harvest several cuts of hay during the summer months to ensure a fodder bank for winter. Eragrostis curvula( E. curvula) also known as “Weeping Love Grass” and “Oulandsgras” was one of four grass species that was selected as a result of the international recognition of the importance of grassland productivity and soil conservation, and is one of the most important pasture grasses in South Africa. E. curvula is easy to establish and generally persists longer than many other species. It has been used with great success for grazing, hay production, a lay pasture after pototo and tobacco production and has played an important role in the prevention of soil erosion by stabilisation of road verges and disturbed soil. There are numerous cultivars available in the market some of which include Ermelo, Agpal, Umgeni, PUK E3, PUK E436 and American Leafy. E. curvula is a tufted subtopical grass with an extensive root system which helps build soil structure. It will survive in areas receiving 400 -1000 mm of rainfall per year and can tolerate soil acid saturations in excess of 70%. It typically grows from September through to March as seen in Graph 1: A well managed pasture may yield four cuts per season if the prevailing conditions are condusive to growth while in drier areas one or two cuts may be achieved. E. curvula yield is a function of rainfall, temperature and nitrogen application and may vary due to geographic location ranging from an excess of 12 tons /ha in the northern areas of the Eastern Cape, Midlands and Northern Kwa Zulu Natal and the cooler areas in eastern Mpumalanga, 6-8 tons/ha in the Free State, 8-10 tons/ha in Gauteng and tapering to 4-6 tons/ha in the western regions of the country. Dry matter yields in excess of 14 tons per ha are attainable with a good fertilization program; even with erratic rainfall, reasonable dry matter and protein yields are attainable, as shown in Graphs 2 – 4 below: Application of N determines dry matter production and improves palatability; additionally, adequate potassium (K) is essential to ensure high yields are maintained. E. curvula is an efficient forager of K, it is important to carry out regular soil tests to ensure that soil K-levels are not ‘mined’ in high production pastures which will result in significant losses in production.  Furthermore, when planning N applications take into…

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By | Soil Health | No Comments

Soil compaction can be a serious yield-limiting factor in crop production, and indications are that this problem is more widespread than is generally perceived. Since compaction is below ground and, thus, not visible, its role in yield decline often goes unnoticed. Soil types Soils vary in their susceptibility to compaction. Research indicates that soils with higher sand and silt contents are more vulnerable to being compacted than loam and clay soils. In addition, the higher levels of organic matter in humic soils reduce their susceptibility to compaction. Causes Management practices that promote compaction include the following: Intensive tillage. Tillage may temporarily loosen the soil; however, in the long-term regular tillage increases the bulk density of soils through the weakening of soil structure and the depletion of soil organic matter. In addition, implements such as the mouldboard plough and disk harrow compact the soil beneath their working depth. Repeated use of these implements can result in the development of plough pans (compacted zones immediately below the ploughed layer (Figure 1, left). Wheel traffic. The wheels of vehicles used to apply fertilizers, lime and other products, harvest crops and pull implements, result in decreases in soil porosity and yield-limiting compaction (Figure 1, right). In the production of annual crops, 60% or more of the soil surface can be trafficked through cultivating, planting, fertilization, herbicide and other chemical applications (Mitchell & Berry, 2001). The in-field traffic associated with maize silage operations and the production of sugarcane frequently results in severe compaction problems (Figures 2 and 3) and associated yield losses. Animal hooves. The role of animals, particularly in intensive grazing systems, in promoting soil compaction is often overlooked. However, although animals are not as heavy as machinery, their weight is applied to the soil in a relatively small hoof-print, and so can cause significant compaction and damage to pastures, thereby decreasing forage yields and animal performance (Figure 4). Importantly, soils are most susceptible to being compacted when they are wet. Unfortunately, timing of farming operations, such as harvesting, fertilizing and rotating livestock, often makes it difficult to exclude machines and animals from soils when wet. Effects of compaction Detrimental impacts of compaction on soil health and plant growth are due largely to the decrease in the proportions of macro-pores in compacted soils. Effects associated with this include the following: Root penetration into compacted soil layers is restricted, and root and biological soil health compromised through water logging and anaerobic conditions in soils. Water infiltration as well as water-holding capacity of soils are reduced, and effective rainfall is diminished through increased runoff. Ponding on the soil surface after rain or irrigation is usually an indication of compaction. Nutrient uptake by roots is poor in compacted soils. This is due to, firstly, limited root development, and secondly, restrictions on the movement of nutrients to roots by mass flow. Yellowing of plants due to nitrogen deficiency is often associated with poor nitrogen recovery by roots in compacted soils. The picture in Figure 2 (left) provides clear…

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