At 15 sites in the cereal belt of New South Wales and Victoria, wheat after lupin or pea produced more biomass and had a greater nitrogen (N) content than wheat after wheat or barley; on average these crops assimilated 36 kg N/ha more. The improved wheat yield after lupin averaged 0 . 9 t/ha and after pea 0.7 t/ha, increases of 44 and 32% respectively. The responses were variable with site, year and legume. Soil available N was increased by both lupin and pea and the levels of surface inorganic N measured at the maturity of first year crops was often related to N in wheat grown in the following year. Of two possible sources of additional N for wheat after legumes, namely mineral N conserved in soil by lupin or pea (up to 60 kg N/ha) and the total N added in the residues of these legumes (up to 152 kg N/ha), both were considered significant to the growth of a following wheat crop. Their relative contribution to explaining variance in wheat N is analysed, and it is suggested wheat may acquire up to 40 kg N/ha from legume stubbles. Non-legume break crops also increased subsequent wheat yield but this effect was not as great as the combined effect of added N and disease break attained with crop legumes.

Wheat response after temperate crop legumes in south-eastern Australia

Genome-wide analysis of 67 ancient Near Eastern cattle, Bos taurus, remains reveals regional variation that has since been obscured by admixture in modern populations. Comparisons of genomes of early domestic cattle to their aurochs progenitors identify diverse origins with separate introgressions of wild stock. A later region-wide Bronze Age shift indicates rapid and widespread introgression of zebu, Bos indicus, from the Indus Valley. This process was likely stimulated at the onset of the current geological age, ~4.2 thousand years ago, by a widespread multicentury drought. In contrast to genome-wide admixture, mitochondrial DNA stasis supports that this introgression was male-driven, suggesting that selection of arid-adapted zebu bulls enhanced herd survival. This human-mediated migration of zebu-derived genetics has continued through millennia, altering tropical herding on each continent.

https://hal.archives-ouvertes.fr/hal-02188455/document

Ancient cattle genomics, origins, and rapid turnover in the Fertile Crescent.

Very little nitrogen (N) fertiliser is applied to wheat crops in Australia. Currently, about 105 t of N fertiliser (less than 20% of Australia's total consumption) are used annually at an average rate of 2-3 kg Nha. This scant use of N fertiliser over much of the Australian wheat belt N is because the N derived from a legume-dominant pasture ley is thought to provide a wheat crop's N requirement. However, trends in the grain protein content of Australian wheat and some other indices of soil fertility suggest that legume-based pastures have not always been able to supply all the N required for adequate nutrition of the wheat crop and that there has been some occasional need for extra N from applications of fertiliser. Recent declines in the productivity and quality of pastures has further increased the need for supplementary applications of N fertiliser. The increase in grain legume production also has been partly based on the presumption that grain legumes contribute to the N economy of the following wheat crop. Many experiments throughout the wheat belt show a yield advantage of wheat grown after a grain legume, but these rotation trials also show that the level of productivity of the grain legume has little effect on the yield of the following wheat crop. A review of these experiments suggests that grain legumes, directly, contribute little to the N nutrition of a following wheat crop and their benefit may be from the legume acting as a disease break or providing the opportunity to control grassy weeds.

The contribution of nitrogen fertiliser to the nitrogen nutrition of rainfed wheat crops in Australia: a review.

In the last 20 years chickpea and faba bean have become major pulse crops in Australia. They are grown during winter over a latitudinal range which extends from 10–40° S for chickpea, and 20–40° S for faba bean. In low latitudes these crops grow mainly on water stored in the soil from summer rainfall with supplementary irrigation in some areas, while in the higher latitudes, they are grown in Mediterranean type environments relying solely on winter rainfall. Farmers recognise the benefit of including these pulses in rotation with cereals and the interest in these crops is continuing to expand, notably faba bean in subtropical north-eastern areas and of both pulses in Western Australia. Breeding programs are continuing to develop cultivars adapted to the wide range of latitudes and with disease resistance. Some germplasm introduced from overseas has required minimal selection before being released, while other genotypes have been poorly adapted and genetic changes are required. Faba bean produces highest yields when sown as early as possible and when diseases are managed by genetic resistance or fungicide application. Chickpea is less affected by delayed sowing and some crops are sown in mid-winter to avoid radiation frosts during early spring. Studies have indicated significant differences between strains of rhizobia in terms of crop growth and the development of acid tolerant strains have been critical for the production of faba bean on low pH soils. A high proportion of both pulses is exported; chickpea to the Indian sub-continent and faba bean to the Middle-East. To meet the requirements of consumers, the effects of the environment on quality are being studied and efforts made to overcome deficiencies through breeding.

Adaptation of chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) to Australia.

Nitrogen fixation, accumulation of soil nitrogen and nitrogen balance for some field-grown legume crops

Two field experiments examined the influence of soil nitrogen on grain yield, wateruse efficiency and residual nitrate accumulation of four winter grain legumes in a legume–fallow–wheat rotation. In the first experiment, conducted on a clay soil with a high total soil nitrogen content (0·194%), the three legumes Cicer arietinum, Vicia faba and Pisum sativum gave similar yields, with Lupinus angustifolius showing poor yields. Water-use efficiencies followed similar trends to the grain yields. Wheat yields and concentration of nitrogen in the grain, following a fallow after the legume crops, showed no differences from a full 2-year fallow. In the second experiment on a low fertility soil (0·081 % total soil nitrogen), Cicer arietinum gave the highest yield and the greatest water-use efficiency. All legumes and long fallow resulted in a similar increase in wheat yield when compared with a wheat-fallow-wheat rotation. The legume crops generally increased soil nitrate status between their sowing and the sowing of a wheat crop 2 years later; such increases were greatest with Pisum sativum at the high fertility site, with a suggestion of the reverse occurring at the low fertility site.

Janet Mahoney

Papers

The effect of soil nitrogen on grain legume yield and nitrogen fixation