Resource requirements for optimal crop production and minimal environmental impact Light Nutrients Water Others? David Midmore Central Queensland University

What practices to optimise use of resources for vegetable crop production No-till/ Minimum-till Cover cropping Agroforestry Gravity (and later pressure?) drip irrigation Others???

Sole crops - easy Light availability Depends upon within- and between- row spacing. Close spacing for early crops, wider spacing for later crops. Close spacing for vegetative yields (total biomass), wider spacing for fruit/tuber crops (reproductive biomass)

Sole crops - easy Nutrient availability Depends upon soil supply, and temporal demand (mineral forms and source – fertiliser, organic sources). Water critical for uptake. Possible deficiency and toxicity, depending upon species and element.

Intercrops, trees with vegetable crops - complicated Light availability Competition for light if different heights, and close by. If tall C4 and shorter C3 species, some complementarity in light use. Issues of taller species row spacing, direction, seasonality, silviculture.

Intercrops, trees with vegetable crops - complicated Nutrient availability Competition for nutrients if similar root zonation. If tree fixes N, some complementarity in N use. Taller species with deeper roots can capture nutrients lost to vegetables, and pump back to surface soil.

Options for over-yielding of vegetables with trees Microclimate modification of understorey crop (more humid, less transpiration, less incident light, cooler) Reduced erosion, soil loss, and therefore more sustainable yields Conserved soil C and CEC and structure enhancing yields

Factors influencing tree-crop interaction (competition and complementarity) Tree functional characteristic (N2-fixing, phosphatase activity, mycorrhizal association) Root architecture (shallow vs deep rooting pattern) Canopy type (erect, broad, large, medium) Seasonality (shedding off leaves, fruiting, etc) Age of trees Quality of tree products (timber or fruits) Types of crop planted (erect vs broad leaves; dicots vs monocots) Soil fertility Soil physical and chemical characteristics Seasons (dry or wet season) Climate Aspects Silvicultural management of trees (spacing, thinning, pruning, etc) Agronomic management of associated crops Temporal demand for water Supply of water Adapted from Jun Mercado (ICRAF)

Courtesy Jun Mercado (ICRAF) Annual cropping plant soil systems

(Leguminous) cover crops with vegetables To gain N as alternative to mineral fertiliser Kill out cover crops before vegetable cropping – easy, and good response on poor soils, but issues of synchrony between supply of N and demand Maintain cover crops with vegetables (live mulch) more difficult Because: competition for space, water, nutrients.

Some cover crop vs. crop arrangements

(Leguminous) cover crops with vegetables Manage timing and spacing to minimise competition Relay intercropping and timing Avoid incorporation if to minimise locking up of soil N Minimal positive long-term effects, and too labour intensive for adoption (in Taiwan)

Water for plant growth Sources: rainfall, irrigation, mist/fog Irrigation: flood, furrow, sprinkler, drip What happens to rainfall/irrigation How much water required by crops and how much supplied by rainfall/irrigation?

Effective rainfall (8) = (1) - (4) - (5) - (7) source: FAO

Infiltration: depends primarily upon soil type and wetness Sandy soilClay soil

Why do crops require water? 80-90% of living plant material is water Plants transpire times their own weight in water What is transpiration? – evaporation from leaf surface, as consequence of getting carbon dioxide in for photosynthesis What is evapotranspiration? – transpiration from canopy plus evaporation from soil Can be closely related to evaporation of water from an open water body, and a crop factor reflecting size, structure of canopy (foliage)

How to measure evaporation?

Can also calculate evapotranspiration with weather data using the FAO Penman- Monteith

Factors influencing crop evapotranspiration Source: FAO

Crop coefficients during growth source: FAO

Crop coefficients at mid-season source: FAO

Water availability in soil to satisfy crop evapotranspiration demand: soil moisture content How express soil moisture content?

Water availability in soil to satisfy crop evapotranspiration demand: soil moisture content Key states: Saturation, Field Capacity, Permanent Wilting point. Availability = FC – PWP [but in practice, for vegetable crops do not let get to PWP]

The available water content depends greatly on the soil texture and structure

Water availability in soil to satisfy crop evapotranspiration demand: soil moisture content How to measure soil water content? Soil based upon feel Gravimetric = ([wet weight of soil – dry weight soil]/[dry weight soil])*100% use balance and oven Volumetric = mm water/100 mm soil depth use neutron probe, TDR, capacitance Water balance = water in soil = [ water input – crop water demand – other water losses (drainage, runoff)] Water potential = measure of energy required by the plant to extract water from the soil use tensiometers, units as –ve pressure, suction, 0 to -0.8 bar

Based upon feel for different soil types

Tensiometers CREDITS: RETURN

Summary Sole crops relatively easy to manage for light, water, nutrients Intercrops, agroforestry, cover-crops requires more management skills Water demands can be measured, calculated, and supplied if necessary by irrigation (later topic)