Chapter 5 Legume–Wheat Rotation Effects on Residual Soil Moisture, Nitrogen and Wheat Yield in Tropical Regions

Flashcards about the effects of legume-wheat rotation on soil moisture, nitrogen, and wheat yield in tropical regions.

What is the primary contribution of grain legumes grown in rotation with annual cereal crops?

They contribute to the total pool of nitrogen in the soil and improve the yields of cereals.

What factors can cause an erratic N benefit from legumes in rotation?

Excessive water use, symbiotic performance, soil pH, biomass returned N, harvest index, and nitrate immobilization during residue decomposition.

In dry land agriculture, what is an important consideration regarding soil water storage?

Soil water storage in the soil profile during the fallow period.

Why might growing a short-term legume in rotation with cereal not adversely affect the following cereal crop yield in a humid climate?

Because of adequate rainfall during the main season for wheat.

How do grain legumes enrich soil N?

Through biological N fixation, which subsequently enhances wheat yields.

What are some non-N benefits of using legumes in rotation with wheat?

Reduction of wheat root rot incidence, enhanced added N uptake, and reduced wheat leaf disease and pests.

According to Boddey et al. (1997), what is needed to increase food production in the tropics?

Crop yields per hectare must be increased without prejudicing the resource base for future generations.

What are some limitations of tropical soils in retaining nutrients and water?

1:1 lattice clays or sesquioxides of relatively low capacity to retain nutrients (CEC) and water (WHC).

What role does crop rotation play in soil management?

Maintenance of soil fertility, improvement of the soil physical environment, control of pests, diseases, and weeds, and control of soil erosion.

What are the primary factors affected by legume rotation that impact crop yields?

Water and N contents of the soil.

According to French (1978b), how does fallowing impact wheat grain yield?

Each millimeter of water stored through fallowing gave an average 8 kg wheat grain per hectare.

In humid tropical environments, what is often inserted into crop rotations to improve soil productivity?

Forage or grain legumes are often inserted into the rotation to improve soil productivity through increased organic matter and N2 fixation.

What is the primary reason for incorporating legumes in cereal rotation?

To benefit soil nitrogen (N) fertility and cereal yields through BNF (Biological Nitrogen Fixation).

What are the two types of benefits associated with including a legume in a crop rotation?

The N effect and the non-N effect.

What factors influence the rate of N2 fixation by legume crops?

Type of legume cultivar, method of measurement, presence of appropriate rhizobia, soil moisture, NO3 level, soil acidity, and P nutrition.

What is the 'nitrate sparing' effect?

The concept that legumes remove less inorganic N from the soil compared with cereals because they obtain N through N2 fixation.

What did Fu (2000) determine about common root rot in wheat-wheat rotations versus chickpea-wheat rotations?

Common root rot severity was 15% greater in the wheat-wheat rotation, indicating chickpea breaks the disease cycle.

What is the role of decomposition in returning biologically fixed N2?

Biologically fixed N2 in legumes is returned to the soil mainly through decomposition of incorporated residues.

How does soil moisture affect microbial activity and N mineralization?

Soil moisture influences microbial activity both directly and indirectly by affecting microbial populations, diffusion of organics, and soil aeration status.

What is the critical C/N ratio for N mineralization to occur?

Application of organic matter having C:N ratio greater than 25 will result in N immobilization, while at lower C:N ratios (e.g., leguminous green manure) mineralization will be preferred.