Jeffrey Evans

Impact of legume 'break' crops on the residual amount and distribution of soil mineral nitrogen

Important factors in the successful uptake of grain legumes by cereal growers have been their capacity to increase soil N and control cereal disease, as these have underpinned high yields in following wheat crops. However, alternative 1-year legume crops are required to introduce additional biodiversity and management flexibility for cereal growers. The effects on soil mineral N and potential contribution to soil total N of other legume enterprises were studied. These included vetch (Vicia bengalhensis) or clovers (mix of Trifolium alexandrinum, T. versiculosum, T. resupinatum) managed for green manure; pea (Pisum sativum), vetch, or clovers managed for silage; and clovers managed for hay. These were compared with pea and lupin (Lupinus angustifolius) managed for grain production. Wheat was also included as a control. The legumes were grown in acidic Red Kandasol soil at Wagga Wagga in southern New South Wales, in 1996, 1997, and 1998. Mineral N was measured in the autumn or winter of seasons 1997 and 1998 respectively. Amounts of stubble residue N were measured in all seasons. The green manure crops, particularly vetch, produced more mineral N than both grain legumes. The forage conservation crops (silage or hay) produced similar amounts of mineral N to grain pea and more than grain lupin. For the grain and green manure legume crops, variation in amounts of mineral N was explained by the total N content of legume stubble residue, but for the forage conservation crops, more mineral N was measured than was predictable from stubble N. The amounts of mineral N at different soil depths differed between legume treatments and experiments (sites and years). Based only on above-ground plant N, the green manure crops contributed more to increasing total soil N than grain legumes; in turn, the grain legumes contributed more than the forage conservation crops. It was concluded that alternative annual legume enterprises to grain legumes may provide at least similar enrichment of soil mineral N early in the following season, and that all annual legume enterprises may accumulate nitrate deep in the soil profile in some seasons. AR Leg ro l mi Jv et al

Impact of annual legume 'break' crops on the yield and quality of canola in comparison with the impact on yield of wheat

This study investigated the yield, oil and protein content of canola in response to alternative single-season legume crops, and compared the yield response with that of wheat. Two field trials were conducted in consecutive years at Wagga Wagga on the South West Slopes of New South Wales. The soil type was Red Kandasol. The legume treatments were field pea and vetch managed for silage production, vetch managed for green manure, a mixture of aerial seeding clovers (Berseem, Arrowleaf, Persian: 6 : 3 : 3) managed for silage, hay or green manure, and field pea and narrow-leaf lupin managed for grain. There was one wheat treatment managed for grain. In terms of growing season rainfall, the rainfall-use efficiency of canola was low and similar to that achieved on farms (5.1 kg/ha.mm rainfall). Yields of canola were less than potential water-limited yields and the canola equivalent wheat yields were less than comparative wheat yields. The constraint(s) on canola yield meant that nitrogen-limited yield potential was not reached, and in contrast to wheat in adjacent plots, there was no relationship between canola seed yield and soil mineral nitrogen available during seedling establishment of canola. However, relative to other legume treatments, antecedent crops of the clover mix depressed yield and total oil content, particularly in one year. It was concluded that under field conditions that constrained canola productivity to that similar to on-farm productivity, wheat may make more efficient use of legume nitrogen than canola. Were canola to be used as the response crop, antecedent legumes of vetch or pea, rather than aerial seeding clover, would give higher potential yield and total oil content of the canola.

Pre-season soil establishment of legume inoculant rhizobia is not effective for the nodulation of lupin and faba bean crops in acidic soils

In soils with a resident population of symbiotically effective rhizobia in sufficient number that legume inoculation is not a requirement for successful legume cropping, greater flexibility may be exercised in the use of legume seed dressings that are toxic to rhizobia. Inoculating crops antecedent to legume crops has been suggested as a method for pre-establishing effective inoculant rhizobia in soil. The extent to which this strategy (pre-inoculation) would remove the need for inoculating legume seed (conventional inoculation) was tested for Bradyrhizobium sp. (Lupinus) and Rhizobium leguminosarum bv. viciae with crops of lupin (Lupinus angustifolius) and faba bean (Vicia faba), respectively. In the glasshouse, in pasteurised sand and red kandosol, the numbers of B. sp. (Lupinus) in the rhizospheres of wheat (Triticum aestivum), canola (Brassica campestris) and clover (Trifolium subterraneum) increased 300-10000-fold over a 14-week period, reaching numbers similar to that achieved on L. angustifolius. These increases were not greatly affected by chemical seed dressings commonly applied to the crops: on wheat, Vincit C and Baytan C; on canola and subterranean clover, Lemat. In the sandy soil, the nodulation of lupin following pre-establishment of rhizobia, drying and mixing of soil, was not improved by conventional inoculation; in the red kandosol nodulation was increased only marginally by conventional inoculation. The results with the glasshouse pot trials warranted further investigation in the field. Under field conditions, when B. sp. (Lupinus) was pre-established with wheat, on a red kandosol in south-western New South Wales, the number of these bacteria surviving in the dry soil at the end of the wheat phase was much lower than in the glasshouse study. In the following season, the nodulation of lupin sown without inoculant, and dependent only on pre-established rhizobia, was significantly reduced, as compared with that on conventionally inoculated lupin. An exception occurred where the lupin was dry-sown 3 weeks before rain, in which case nodulation was comparatively poor even with conventional inoculation. Reduced nodulation was generally consistent with initially fewer rhizobia in the lupin rhizosphere. However, the numbers of rhizobia were eventually similar to those found with conventional inoculation. In the third year, in autumn, B. sp. (Lupinus) was abundant in the soil in all treatments and there were no differences in lupin nodulation between treatments. Similarly, introducing R. leguminosarum bv. viciae on wheat, in an acidic red kandosol in south-western New South Wales, failed to provide as much nodulation of faba bean as was achieved with conventional inoculation. The maximal dry matter of the bean crop was also significantly lower with pre-inoculation as compared to conventional inoculation.

Improving Sustainable Production of Maize on Upland Soils of the Democratic People's Republic of Korea

Maize production in the Democratic Peoples Republic of Korea is limited by soil infertility. Trials were established at two cooperative farms to quantify the yield response of maize to fertilizer and to vetch green manure. Crop land is precious so the vetch had to be integrated either by a short growth period prior to the crop in spring, or risking an autumn sowing for growth over winter. Maize grain yield was linearly related to the amount of vetch incorporated before maize at an annualized rate of 77–121 kg grain per fresh weight ton of vetch manure. The N fertilizer substitution value was about 60 kg N ha−1 as urea. This response may be increased by adopting more cold-tolerant vetch (or alternative legumes), and safeguarding vetch from villagers livestock.

Towards a more productive and sustainable cropping system in the Democratic People's Republic of Korea. I. Rice production.

To improve food security in the Democratic Peoples Republic of Korea, an increase in grain production is essential. However, the access to and affordability of fertilizer is limited. At two cooperative farms (Hyongsan and UnSong) in the central western grain-producing region, field trials with rice were established in 2002 and continued to 2005. The aim was to quantify the yield response of lowland rice to a legume green manure (hairy vetch; Vicia villosa) sown in autumn-winter of each year. In other cropping treatments one, two or all vetch crops in the three-year sequence were replaced by wheat, or by fallow (traditional). Thus, over the course of the experiment the number of vetch crops relative to rice crops (vetch : rice) varied 1.0, 0.67, 0.33, and 0.0 between the rotation treatments. Each rotation treatment was amended with nil or plus urea (60 kg N/ha) applied only to the rice crop. Basal nutrients of P, K, and Mo were applied to all treatments and the continuous rice-fallow and rice-wheat rotations were duplicated without the basal nutrients. The yields of rice sites were limited by N fertility. Rotations that included vetch supported significantly higher mean rice yields than the continuous rice-fallow or rice-wheat rotations. In the absence of urea, the mean yield of rice in the treatment with vetch : rice = 1.0 was 0.55 t/ha (12%) greater than the yield in the rice-fallow treatment, and was 68% of the mean rice yield achieved with the annual applications of urea in the rice-fallow rotation. The yield of rice was positively related to the amount of vetch preceding each rice crop, and the mean annual gain in rice yield was estimated at 67 kg/fresh weight tons of vetch/ha. However, the biomass of vetch was severely reduced in some plots by waterlogging, by grazing or foraging, and by cold sensitivity such that improved vetch management may feasibly support greater increases in rice yield. A combination of both urea and vetch produced the highest mean rice yields, but it also increased the risk of blight in rice. It was concluded that widespread adoption of winter legume green manuring in the DPRK would significantly improve food security and reduce reliance on urea aid; however, further research is required to optimize this strategy for rice yield.