Here, we analysed a wide range of literature data on the leaf dry mass per unit area (LMA). In nature, LMA varies more than 100-fold among species. Part of this variation (c. 35%) can be ascribed to differences between functional groups, with evergreen species having the highest LMA, but most of the variation is within groups or biomes. When grown in the same controlled environment, leaf succulents and woody evergreen, perennial or slow-growing species have inherently high LMA. Within most of the functional groups studied, high-LMA species show higher leaf tissue densities. However, differences between evergreen and deciduous species result from larger volumes per area (thickness). Response curves constructed from experiments under controlled conditions showed that LMA varied strongly with light, temperature and submergence, moderately with CO2 concentration and nutrient and water stress, and marginally under most other conditions. Functional groups differed in the plasticity of LMA to these gradients. The physiological regulation is still unclear, but the consequences of variation in LMA and the suite of traits interconnected with it are strong. This trait complex is an important factor determining the fitness of species in their environment and affects various ecosystem processes.

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Causes and consequences of variation in leaf mass per area (LMA): a meta-analysis.

This article reviews literature about the impacts of cover crops in cropping systems that affect soil and water quality and presents limited new information to help fill knowledge gaps. Cover crops grow during periods when the soil might otherwise be fallow. While actively growing, cover crops increase solar energy harvest and carbon flux into the soil, providing food for soil macro and microrganisms, while simultaneously increasing evapotranspiration from the soil. Cover crops reduce sediment production from cropland by intercepting the kinetic energy of rainfall and by reducing the amount and velocity of runoff. Cover crops increase soil quality by improving biological, chemical and physical properties including: organic carbon content, cation exchange capacity, aggregate stability, and water infiltrability. Legume cover crops contribute a nitrogen (N) to subsequent crops. Other cover crops, especially grasses and brassicas, are better at scavenging residual N before it can leach. Because growth of thes...

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Using winter cover crops to improve soil and water quality

/pdf/replacing-bare-fallows-with-cover-crops-in-fertilizer-1dx7gdqe2s.pdf

Replacing bare fallows with cover crops in fertilizer-intensive cropping systems: A meta-analysis of crop yield and N dynamics.

Intercropping, the agricultural practice of cultivating two or more crops in the same space at the same time, is an old and commonly used cropping practice which aims to match efficiently crop demands to the available growth resources and labor. The most common advantage of intercropping is the production of greater yield on a given piece of land by making more efficient use of the available growth resources using a mixture of crops of different rooting ability, canopy structure, height, and nutrient requirements based on the complementary utilization of growth resources by the component crops. Moreover, intercropping improves soil fertility through biological nitrogen fixation with the use of legumes, increases soil conservation through greater ground cover than sole cropping, and provides better lodging resistance for crops susceptible to lodging than when grown in monoculture. Intercrops often reduce pest incidence and improve forage quality by increasing crude protein yield of forage. Intercropping provides insurance against crop failure or against unstable market prices for a given commodity, especially in areas subject to extreme weather conditions such as frost, drought, and flood. Thus, it offers greater financial stability than sole cropping, which makes the system particularly suitable for labor-intensive small farms. Besides, intercropping allows lower inputs through reduced fertilizer and pesticide requirements, thus minimizing environmental impacts of agriculture. However, intercropping has some disadvantages such as the selection of the appropriate crop species and the appropriate sowing densities, including extra work in preparing and planting the seed mixture and also extra work during crop management practices, including harvest. The selection of an appropriate intercropping system for each case is quite complex as the success of intercropping systems depend much on the interactions between the component species, the available management practices, and the environmental conditions. Plant breeding can contribute determinedly to increase of productivity of intercropping systems by investigating and exploiting the genetic variability to intercrop adaptation. This paper provides an overall view and evaluation of annual intercropping, summarizing its main advantages supported by a number of key examples from the literature which point out its great value in the context of sustainable agriculture.

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Annual intercrops: an alternative pathway for sustainable agriculture.

Source-sink regulation by sugar and stress

http://directory.umm.ac.id/Data%20Elmu/jurnal/E/European%20Journal%20of%20Agronomy/Vol12.Issue2.March2000/3.pdf

Intercropping corn with soybean, lupin and forages: yield component responses

Morphology and yield response to weed pressure by corn hybrids differing in canopy architecture

Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec, Canada, and in 1996 at Ottawa, Ontario, Canada, to quantify the impact of corn hybrids, differing in canopy architecture and plant spacing (plant population density and row spacing), on biomass production by transplanted and naturally occurring weeds. The treatments consisted of a factorial combination of corn type (leafy reduced stature [LRS], late-maturing big leaf [LMBL], a conventional Pioneer 3979 [P3979], and, as a control, a corn-free condition [weed monoculture]), two weed levels (low density [transplanted weeds: common lambsquarters and redroot pigweed] and high density [weedy: plots with naturally occurring weeds]), two corn population densities (normal and high), and row spacings (38 and 76 cm). At all site-years under both weed levels, the decrease in biomass production by both transplanted and naturally occurring weeds was greater due to the narrow row spacing than due to the high plant population densi...

Weed Biomass Production Response to Plant Spacing and Corn (Zea mays) Hybrids Differing in Canopy Architecture1

Intercropping corn with soybean, lupin and forages: weed control by intercrops combined with interrow cultivation

The use of high rates of N fertilizer in intensive sweet corn (Zea mays L) production may result in leaching losses and contamination of adjacent waterways and ground water Cover crops planted after sweet corn harvest could absorb residual soil N and minimize losses of fertilizer in gravitational water Field experiments were conducted on a Ste Rosalie heavy clay (fine, mixed, frigid, Typic Humaquept) and a St Bernard sandy clay loam (fine loamy, mixed, nonacid, frigid Typic Eutrochrept) Cover crop effects on nutrient uptake, subsequent N release, loss of N, P, and K in leaching water, and denitrification rates were measured Fertilizer N rates were 0, 75, and 150 kg ha -1  Cover crops were red dover (Trifolium pratense L), crimson clover (Trifolium incarnatum L), forage radish (Raphanus sativus L), canola (Brassica rapa L), barley (Hordeum vulgare L), and annual ryegrass (Lolium multiflorum L) A control treatment with no cover crop was also included Three replicates were used in a split-plot arrangement of a randomized complete block design Fall residual soil NO 3 - -N levels were higher in control plots than cover crop plots Gravitational water NO 3 - -N was greater in control plots and ranged from 17 to 76 kg N yr -1 N, compared with cover crop plot values of I to 55 kg N yr -1  Cover crops had no effect on denitrification rates, or on NH 4 + -N, P, or K concentrations in gravitational water Forage radish, canola, and barley were effective cover crops in reducing soil NO 3 - -N Cover crop effects on subsequent sweet corn were found only in grain N uptake

Daniel C. Cloutier

Papers

Intercropping corn with soybean, lupin and forages: yield component responses

Morphology and yield response to weed pressure by corn hybrids differing in canopy architecture

Weed Biomass Production Response to Plant Spacing and Corn (Zea mays) Hybrids Differing in Canopy Architecture1

Intercropping corn with soybean, lupin and forages: weed control by intercrops combined with interrow cultivation

Cover Crops and Nutrient Retention for Subsequent Sweet Corn Production