growth and production of sorghum and millets

GROWTH AND PRODUCTION OF SORGHUM AND MILLETS

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GROWTH AND PRODUCTION OF SORGHUM AND MILLETS P.V. Vara Prasad and Scott A. Staggenborg Department of Agronomy, Kansas State University, Manhattan, KS 66506 Keywords: Barnyard millet, crop management, drought stress, finger millet, foxtail millet, genetic resources, growth and development, kodo millet, proso millet, sorghum. Contents 1. Introduction 2. Sorghum 3. Pearl Millet 4. Finger Millet 5. Proso Millet 6. Foxtail Millet 7. Little Millet 8. Barnyard Millet 9. Kodo Millet 10. Conclusions Acknowledgements Related Chapters Glossary Bibliography Biographical Sketches Summary Sorghum and millets are important crops for food security in semi-arid and arid regions due to their high nutritional quality, tolerance to stresses (abiotic and biotic) and their performance in marginal lands with relatively low fertility. Utility of these crops is diverse (food, brewing, feed, forage, fodder, biofuel, and building material). In Africa and Asia sorghum grain is mainly used as food, while, in the United States and Australia it is used to feed cattle. More recently in India and Africa, it is being used as poultry feed. Sorghum and millets are also gluten free and can be important food sources to millions of people who are intolerant to gluten (celiac disease), including diabetic patients, in both developed and developing countries. Sorghum also shows high potential as a bioenergy crop due to its high biomass production, photoperiod sensitivity and sweet stalks. Millets have a wide range of crop cycles, and some have even a very short cycle, which makes them fit quite well in several cropping systems. Under subsistence farming sorghum and millets are grown with limited resources. However, both crops generally respond well to fertilizer inputs and can provide interesting economic yield benefits. Despite high yield potential, the productivity of sorghum and millets in farmers’ fields is low, mainly since these crops are being pushed to more marginal farmlands. Sorghum and millets will continue to play a key role in providing food security in subsistence cropping systems of Asia and Africa, and in improving economic returns to

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large farmers in the assured rainfall regions of the world. Research and extension activities towards crop improvement, intensified cropping systems and improved management of soil, water, nutrients and weeds will help produce higher yields. 1. Introduction Sorghum and millets are important food crops in semi-arid and arid regions of Africa and Asia, where they perform rather well under harsh climatic conditions in marginal lands with low fertility. Besides their function as a food crop to the local populations they are also used, especially in developing countries, as cattle and bird’s feed, forage and fodder, and more recently as bioenergy crops. Sorghum is a staple cereal food crop for more than 500 million people. Sorghum grain is mostly consumed for food purpose (55%) as flat bread and porridges in several countries of Asia and Africa. In dry season the sorghum stalks are used as feed for livestock, especially in Asia. In America, grain sorghum is an important animal feed in addition to forage sorghum. Millet is a collective term commonly referred to a number of small seeded annual grass grain crops. Millet production is generally limited to fields with low soil fertility and poor rainfall conditions. Although millet production is only about 2% of the world cereal production, it is an important staple food crop in semi-arid regions. Asia and Africa account for about 95% of the total millet production in the world. Asia accounts for 40% of millet production, mainly contributed by India and China. Africa accounts for 55% of total production, mainly concentrated in Nigeria, Niger, Burkina Faso, Mali, and Kenya. Very limited quantities of millet are produced in developed countries primarily for high value specialty markets for human nutrition or bird feed. The most common species of millet include pearl millet (Pennisetum glaucum), finger millet (Eleusine caracana), proso millet (Panicum miliaceum), foxtail millet (Seteria italica), little millet (Panicum sumatrense), barnyard millet (Echinochloa colona) and kodo millet (Paspalum scrobiculatum). Sorghum and millet’s genetic resources are conserved at many centers around the world. One of the major organizations which maintain sorghum and millet germplasm and that has a global mandate for sorghum and millet improvement is the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) located in Patancheru, Andhra Pradesh, India. At global level sorghum germplasm collections consists of about 168,500 accessions. ICRISAT has the largest single collection of sorghum (about 22% of the global total germplasm) with a total of 36,774 accessions from 91 countries. This collection is estimated to represent about 80% of the variability present in sorghum. Other organizations include the National Plant Germplasm System (NSPS) in USA, Ethiopia, Sudan, South Africa, India, and China. Despite the large accessions of sorghum, only a very small proportion (12 h). Similarly, photoperiod-sensitive temperate cultivars have longer photoperiod requirements (around 13.5 h) and would, thus, not flower in tropical regions. As the photoperiod changes with latitude (both north and south), as well as with time of the year in temperate regions, care should be taken while selecting cultivars or hybrids based on photoperiod sensitivity, and duration of critical photoperiod. 2.4.2. Temperature Average soil temperature for seed germination ranges from 4.6 to 16.5ºC. Optimum soil temperature for germination ranges from 21 to 35ºC, with a maximum temperature up to 40-48ºC. For leaf appearance, the minimum temperature ranges from 7 to 12 °C, with an optimum between 26 and 34°C. Temperatures above the optimum decrease the rate of leaf appearance. Leaf elongation rate linearly increases from 13 to 32°C and declines above 34°C. The minimum and maximum temperatures for leaf elongation are 15.5 and 43°C, respectively. The base temperature for panicle initiation is from 6.8 to 10.4°C, and the optimum is from 25.9 to 27.3°C; maximal allowed temperatures range from 36.8 to 58.9°C. The response to temperatures above or below the optimum is linear and delays panicle initiation. Grain yield is a product of grain number per unit area and grain weight. Grain number per unit area is determined by number of plants and number of grains per plant. Grain number per plant is determined during panicle initiation and flowering stage (GS2). High or low temperatures during this stage significantly influence flower production and the ability of flowers to set seed. High temperatures above 32/22ºC (daytime maximum/nighttime minimum) cause abortion of flowers resulting in lower seed-set and grain numbers. The two stages of grain sorghum reproductive development most sensitive to high temperature stress are flowering and 10 days before flowering. High temperature stress during these periods in the growth cycle cause maximum reduction in seed-set, seed numbers, and seed yields. Early seed-filling periods are relatively more sensitive to high temperature stress compared with later periods. Seed yield losses during post-flowering stages are mainly due to decreases in seed size. The maximum potential grain number is set by the end of GS2 and final grain yield is dependent upon number of filled grains and individual grain weight. Grain weight is a product of two factors: rate of grain filling and duration of grain filling process. Both these processes are highly sensitive to temperature. High temperatures (>36/26 °C) decrease both the rate of grain filling and grain filling duration, and result in lower yields. Similarly, cool temperatures ( 800 mm coupled with adequate distribution (spread coinciding with panicle initiation, flowering and grain filling stages). Adequate soil moisture is required for proper germination and establishment. Although the amount of water taken up during emergence and seedling establishment is low, it is critical for initial plant population. Soil water use gradually increases from emergence, reaching a maximum at flowering, and gradually decreasing there after until maturity. Daily water use about 3 – 5 mm/ha depending upon growth stage and it can reach a maximum of about 6 – 7 mm /ha for few days. Maximum daily water use is highest during booting to seed-set. Water use and requirement decline rapidly after soft dough stage. For maximum yield adequate soil moisture should be available during two critical stages of crop development. Firstly, prior to booting to help set high yield potential and panicle exsertion, and secondly at flowering help seed-set and early grain filling. In most sorghum production regions, crop is exposed to drought stress during both the pre- and post-flowering stages. Drought stress during late vegetative phases (pre-flowering) significantly affects panicle exsertion and influences the reproductive potential. Drought stress during flowering decreases seed-set, and stress during post flowering stages can decrease grain size. The extent of yield losses due to drought depends on the intensity, duration and timing of stress. Crop improvement efforts are focused on improving drought tolerance during both pre- and post-flowering stages. Sorghum adopts both escape and tolerance mechanisms. Plants escape drought through the development of an extensive root system and by optimizing water use. Under severe drought conditions, sorghum becomes dormant and stops growth before floral initiation and remains vegetative until favorable conditions occur. The total water requirement for sorghum is much lower than that of corn. The crop also has higher water use efficiency than maize and, thus, performs better than maize in dry semi-arid regions. 2.5. Soil Requirements Sorghum is adapted to a wide range of soils. Sorghum can grow in light sandy soils, but higher yields are obtained in well drained loamy soils with good fertility. Yields of sorghum are generally greater in soils with high organic matter. Soil reaction (pH) influences sorghum production directly by affecting plant growth and development, and indirectly by affecting the solubility and availability of nutrients. Sorghum is generally grown in almost neutral (pH 6.5 to 7.0) to moderately alkaline (pH 7.0 to 8.3) soils. Optimum soil pH is 6.5 to 7.8; development and yield are hampered in soils with pH below 5.7 or above 8.3. Liming is recommended in soils with pH below 5.7 to improve nutrient availability and avoid aluminum toxicity. Similarly, acidification (for example through the application of acidifying fertilizers) is recommended in soils with high pH and/or free lime which induce iron deficiency and lower yields. Although sorghum is relatively more tolerant to soil salinity than wheat and rice, the presence of salts often limits production, particularly in low rainfall regions. Accumulation of excess salts, particularly Ca and Mg in the form of chlorides and

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sulfates (saline soils), and of sodium (sodic or alkali soils) decreases plant growth and development. Sorghum is particularly sensitive to salts during germination and early vegetative growth, but becomes more tolerant at later stages of vegetative development. Physical soil amendments aiming to remove excess salts through leaching, or chemical amendments to adjust soil acidity and ameliorate the nutrient status in the root zone improve the productivity of sorghum in problem soils. 2.6 Crop Management Adoption of good and adequate crop management practices such as an appropriate cropping system, crop rotation, selection of cultivar, optimum time of planting, proper fertilization and irrigation, integrated weed and pest (diseases and insects) management strategies all lead to higher and better yields. 2.6.1. Cropping System Cropping systems for grain sorghum production vary depending upon the region and availability of soil moisture. Areas with adequate soil moisture retention may practice continuous cropping of grain sorghum. Though continuous cropping might lead to nutrient mining, appropriate management techniques and fertilizer applications can avoid such detrimental effects to soil. In general, proper crop rotations minimize weed, insect and disease hazards. Common crop rotations in Africa and Asia include sorghum-legume or legume-sorghum production systems. The selection of the legume depends upon the region. For example in West Africa commonly rotated legumes include groundnut (Arachis hypogaea L.) or cowpea (Vigna unguiculata L.); in south Asia it involves groundnut, black gram (Vigna mungo L.), green gram (Vigna radiate L.), soybean or cowpea. In several parts of the United States rotations of sorghum – soybean (Glycine max L.) or sorghum – cotton (Gossypium hirsutum L.) are a common practice. 2.6.2. Cultivar or Hybrid Selection Use of hybrids is common and widespread in developed countries such as the United States, Europe and Australia. However, in several developing countries (particularly in Africa and to a lesser extent in Asia) hybrids are not common. There is a wide range in duration to maturity in sorghum cultivars and hybrids (from 90 to more than 150 days). Cultivar or hybrid selection is highly dependent upon the length and characteristics of the growing season (environmental constraints, particularly temperature and occurrence of frost) and soil water retention capacity. Selection of cultivars linked to maturation, early or late planting are all dependent on weather conditions. In addition, due to its high photoperiod and temperature sensitivity, the selection of sorghum cultivars and hybrids with a good yield potential and performance, is often region- and season-specific. Producers should select cultivars or hybrids that take advantage of longer growing seasons for higher yields and/or that avoid high temperatures or moisture stress during sensitive stages of reproductive development. In general, a long duration cultivar or hybrid extending over the full season will produce better yields than early and short-duration cultivars, even under favorable management and environmental conditions. In recent times availability of crop simulation models help answer ‘what if ?’ strategies. However under low rainfall and unfavorable temperature conditions early season varieties might be more beneficial.

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2.6.3. Seedbed Preparation Seedbed preparation is an essential part of crop management to improve rain water infiltration, conserve moisture and decrease weed pressure, with the ultimate goal to facilitate germination. Seedbed preparation should begin soon after harvest of the previous crop. This generally includes the removal of stalks, disking the soils and leveling (harrowing) the surface. However, in recent year’s no-tillage cropping system is gaining importance which limits the use of tillage equipment (see also: Conservation Agriculture). No-tillage is becoming rather common in the United States and South America due to benefits of improving the soil organic carbon level, reducing erosion and increasing moisture holding capacity of soil over long periods. No-tillage cropping systems are best suited for moderately and well drained soils. In addition, the availability and cost of herbicides to control weeds also plays an important role in the adoption of a no-tillage planting system. In India, especially in coastal Andhra Pradesh state, where irrigation water during the rabi (post rainy) season is hardly available, there is a shift from rice-rice to rice-maize or rice-sorghum production systems. Zero-tillage is being practiced to conserve the soil moisture from the rice crop and with two to three irrigations a successful sorghum crop is being grown. 2.6.4. Planting Date Planting dates are determined by local and seasonal conditions and are therefore regionspecific. The planting date depends on availability of soil, air temperature and soil moisture for proper germination. Cool soil temperatures often limit germination. Soil temperature above 10 ºC at planting depth is essential. Minimum soil moisture at the time of germination and early growth is required as well. Typical planting times in the northern hemisphere in Asia (rainy season), Africa and United States vary from June to July depending upon minimum temperature and frost risk, and on the occurrence of adequate rainfall (or the availability of an irrigation system). Post rainy season sorghum in India is planted during the September to October sowing window, dependent mainly on residual soil moisture. Planting dates of sorghum in Australia, and the southern hemisphere in general, range from December to January. Planting is delayed if adequate soil moisture or irrigation facilities are not available. 2.6.5. Plant Population and Spacing Sorghum is propagated through seed, which is directly sown in the soil. In the United States, Australia and other developed countries tractor operated seed drills are commonly used, while in developing countries in Asia and Africa, hand sowing or handand animal-drawn seed drills are used. The seed rates depend upon the size of seeds, test seed weight and number of seeds per kg. In regions with low soil moisture, wider row spacing and fewer plants per hectare are recommended. Seeding rates vary from 3-4 kg/ha in dry areas to 8 to 10 kg/ha under irrigation. Row spacing and intra-row spacing depend upon the availability of soil moisture and planting equipment. Under favorable conditions a spacing of 50 to 60 cm between the rows and 12 to 20 cm from plant to plant in the rows is recommended. Plant population is around 120,000 plants per hectare under favorable conditions. Depending upon the emergence

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percentages (typically between 70 and 80%) the seeding rate should be adjusted. The seeding depth depends upon soil type. Typical planting depth ranges from 2 to 3 cm in heavy soils and from 3 to 5 cm in sandy soils. Planting too deep (> 5 cm) causes poor seedling survival and vigor, while planting too shallow (