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

Abstract

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.

Soil mineral nitrogen benefits derived from legumes and comparisons of the apparent recovery of legume or fertiliser nitrogen by wheat

“…In keeping with the findings of other previous studies undertaken in Australia and elsewhere in the 465 world, concentrations of soil mineral N were significantly greater following legumes compared to after 466 non-legumes (e.g. Evans et al 2003;Miller et al 2003;Angus et al 2015). In absolute terms the 467 magnitude of the effect of legumes varied across locations, years and whether the crop was harvested 468 for grain or terminated during spring as a BM crop (Tables 3-5).…”

“…Each of these processes can be influenced by: 80 (i) the duration of the period of fallow between the end of one cropping season and the beginning of the 81 next since this defines the time available for weed growth, and mineralisation or loss processes to occur 82 (iii) the quantity of plant residues remaining at the end of the previous growing season and the N content 87 (or C:N ratio "quality" attributes) of those residues. Residue N content determines the amount of N 88 potentially available for mineralisation (Evans et al 2003), and C:N ratio influences whether a net 89 release or immobilisation of mineral N occurs (Russell and Fillery 1999; Kumar and Goh 2000;Fillery 90 2001). 91…”

“…2015). This is usually attributed to elevated availability of soil mineral N and healthier wheat crops 94 recovering more soil N following legumes (Evans et al 2003; Angus et al 2015). But while the 95 principles associated with legume-induced improvements in soil mineral N are well known, previous 96 studies have invariably been undertaken on experimental stations rather than under the prevailing abiotic 97 and biotic constraints and cultural conditions typically experienced by commercial crops in farmers' 98 fields.…”

A review of organic carbon accumulation in soils within the agricultural context of southern New South Wales, Australia

“…This realisation increased the popularity of green and brown manure crops, that is, legume crops that are grown until early pod formation and then terminated by tillage or herbicide (Evans et al, 2003). The question remains as to whether such a system can be economically used often enough to improve net N balance in the soil.…”

Field measurement of lupin belowground nitrogen accumulation and recovery in the subsequent cereal-soil system in a semi-arid Mediterranean-type climate

“…They offer a pest and disease break, improve soil structure and input N to the system via biological nitrogen (N) fixation (Siddique and Sykes 1997), although in recent years economic and agronomic constraints have contributed to a decrease in area sown (Evans et al 2003). The narrow-leaved lupin (Lupinus angustifolius) has been a particular success on coarse textured neutral to acid sands across the wheat growing regions of Australia, directly providing economic gains via high grain yields but also indirectly increasing the grain yield and protein of subsequent cereal crops (Evans et al 1991(Evans et al , 2001Heenan et al 1998;Rowland et al 1988).…”