4.3 Irrigated corn best practice guide

Transcription

1 Bec Raymond DAFF Queensland Graham Harris DAFF Queensland Key points Water required varies from 500 to 800 mm A full irrigation strategy or limited water irrigation strategy can be used Waterlogging can be as detrimental to corn as insufficient water The period from tasselling, through silking and until the end of dough is the most sensitive to water stress. The timing of the last irrigation will depend on your soil type, available water and the dent stage of the crop Where water is limited the yield target must be reduced and appropriate irrigation strategies used Corn has a high demand for nitrogen, phosphorus and potassium Choose the most appropriate hybrid maturity for your location, planting time and available water Match plant populations to hybrid choice and available water Plant when soil temperature is above 120C at 9am and rising, and aim to avoid flowering during mid-summer, and frost during seedling and before physiological maturity Plant Water Use Corn produces large amounts of dry matter and grain where adequate water is supplied. For maximum production a medium maturity corn grain crop requires between 500 and 800 mm of water depending on the climate. The amount of water required to produce a corn crop with maximum yield is not a fixed value as temperature and relative humidity during the growing period, along with wind and soil moisture, all determine the rate of evaporation from the soil and transpiration from the plant (evapotranspiration or ET C ). The DAFF Queensland free online tool CropWaterUse can be used to examine the seasonal variability in crop water requirement for fully irrigated corn at your location. Table summarises the output from CropWaterUse used to estimate the irrigation needed to grow corn at three locations (Dalby, Goondiwindi and Emerald) for a 1 September sowing date. The analysis assumes that the crop is fully irrigated to target maximum yield. An irrigation application efficiency of 75% and a 75mm irrigation target deficit are assumed. Results show a large variation in seasonal crop water demand, rainfall and irrigation demand between locations and season types. Figure shows the daily water use in corn which peaks during silking and tasseling (VT to R1). Nearly 24 percent of the total water demand by the crop occurs in this three week period. From week 5 to week 11 a fully irrigated corn crop will use 71 per cent of its total water requirement. The area of irrigated corn to plant is a function of corn price, available water and your planned irrigation strategy. Irrigation Strategies Full Irrigation Table summarises the impact of excessive and inadequate water on corn at different growth stages. Key points to consider for fullyirrigated corn are: Evapotranspiration (ET C ) is usually linearly related to crop yield. Stressing the crop at any stage of development reduces ET C and yield. This yield loss cannot be recovered by irrigating at a later time. Corn planted at the optimum time should not need irrigation before the V4 stage. There is usually adequate soil moisture just below the dry soil surface and ETC is usually low at this time due to lower temperatures early in the crop season. Section 4: Irrigation management of grain crops 305

2 Table Comparison of average water requirements for corn planted on the 1 September at Goondiwindi, Dalby and Emerald, based on historical weather data (1957 to 2008) Goondiwindi Dalby Emerald Season Type Dry Ave Wet Dry Ave Wet Dry Ave Wet Crop ET C (mm) In-crop Rainfall (mm) Irrigation Demand (ML/ha) No. of Irrigations As the crop begins more rapid vegetative growth and temperatures increase it is important to keep the plant available water content (PAWC) between 50% (the refill point) and 100% (full point). Remember that waterlogging can be as detrimental to corn as water deficit. The period beginning just prior to tasseling (VT) and lasting into the milk stage (R3), especially at or near silk emergence (R1) is the most important period for water supply to the crop. Daily water use varies throughout the season depending on weather conditions and stage of growth (see Figure 4.3.1). The crops ability to take up water increases as the canopy develops, peaking at the silking stage (R1). Hot, drier conditions will increase the crop s water requirement and taller crops with thicker canopies require more water than shorter crops. Figure Average daily water use pattern for corn and critical growth stages Water Use 8 mm/day 7 mm/day 6 mm/day 5 mm/day 4 mm/day 3 mm/day 2 mm/day 1 mm/day 0 mm/day Stage Week VE V1 V3 V7 V10 VT R1 R Chart for a 1 September planted crop at Dalby daily water use values for hotter districts like Emerald would be 10 to 20% higher. 306 WATERpak a guide for irrigation management in cotton and grain farming systems

3 Yield reductions of up to 50% can occur if the corn is wilted for four days at the end of the pollination period (R0). Even in the dough stage (R4) four consecutive days of wilting can reduce yield by 40%. However, four days of wilting at least a week prior to tasseling (VT) may only result in a 10% yield reduction. Water management during the grain filling period is vital. This period for corn is 1/3 longer than for grain sorghum The decision to stop irrigation needs to take account of crop stage, soil type and PAWC. There needs to be enough water to fill out the grain while saving water and energy. Corn reaches physiological maturity about 2 weeks after the full dent stage (R5), and the crop normally requires about 60mm of water during this period. Sandy soils require a fully recharged profile to supply this much water and on these soils irrigation should not be stopped until a week after full dent. For heavier textured clays the necessary 60mm can be held in around 30cm of moist soil, and irrigation may be stopped 4 to 5 days after early dent, even before the full dent stage. Irrigations can be scheduled based on soil moisture monitoring using one of the commercial soil moisture monitoring tools available. This equipment can tell you the rate of crop water use and the depth of water extraction. This can be used to make irrigation scheduling decisions. Irrigation can also be scheduled based on estimation of crop ET C from weather data. Watersched2, a free online irrigation scheduling tool developed by DAFF Queensland is now available. This tool automatically downloads daily weather data from different locations in Queensland and New South Wales and using farmspecific inputs conducts a daily soil water balance and economic analysis to determine when and how much to irrigate. Figure is an example of the end of season report generated by WaterSched2 for an irrigated corn crop at Dalby in the season. This report summarises the water, crop and economic data for the crop. It provides the WUE indices for predicted and actual yield achieved. The graph at the bottom of the report shows the daily soil water depletion. During the season, this report provides the information needed by the grower to decide on their most appropriate irrigation scheduling strategy in response to crop water requirements, likely economic returns and whole farm water availability. Limited Water Strategies If there is a high probability of reduced water allocation and insufficient rainfall, then the yield target may need to be revised down, and supplementary irrigation strategies adopted. Supplementary irrigated crops are water limited there is not enough water available to fully irrigate the area to be sown. Growers faced with this situation have two main choices: 1. maximise production per hectare by growing an area that can be fully irrigated from the water available 2. grow the largest possible area possible where irrigation is only applied during the most critical growth stages. Growers wanting to maximise productivity per ML of water will need to strike a balance between these options based on their local conditions and climatic forecasts. Growing a smaller, fully irrigated area of crop may limit the potential upside but avoids the extra costs associated with growing a larger area. On the other hand, yield may be poor if a larger area is planted and seasonal conditions are not favourable. Where the crop cannot be fully irrigated and a limited water strategy is being implemented it is important to time the first in-crop irrigation prior to tasselling (VT). Follow-up irrigations should be applied during the silking (R1) and blister (R2) stage. If possible, irrigation should be continued through until the end of the dough stage to prevent wilting. Stress late in the season (from dent stage to maturity) has the least impact on yields so irrigation should cease at these stages. Section 4: Irrigation management of grain crops 307

4 Table Critical crop management considerations by growth stage for corn Stage Week Description Crop Management Consideration Seedling VE 0 Emergence If soil is too wet, too cold or too dry, germination V1 1 Collar of first leaf visible. will be slow and young seedlings may die before establishment. Shortages of major elements may slow growth and development. V2 2 2 leaves fully emerged All leaves are formed during the first 3 weeks V5 3 5 leaves fully emerged of growth by a single growing point below the ground surface. Wet or dry conditions will slow seedling growth. Plants are susceptible to flooding, especially if temperatures are high. Vegetative V leaves fully emerged. Tassel and ear initiation. Around 30 days after planting the growing point is at the ground surface and, having formed all the leaves, develops into an embryonic tassel. V leaves The plant has a high requirement for nutrients V Leaves and water. Water stress will restrict leaf cell growth resulting in smaller leaves, a shorter plant Vn 8 n leaves and less yield potential. The plant undergoes rapid vertical growth and the roots rapidly fill most of the root zone. Cob size is determined over this period the number of rows per ear first, then kernels per row. Flowering and Fertilization Grain filling and Maturity VT 9 Last branch of tassel completely visible R0 10 Athesis or male flowering. Pollen shed begins. R1 11 Silks are visible. R Blister stage. Kernels are filled with clear fluid and the embryo can be seen. R3 R4 R5 Milk stage. Kernels are filled with white, milky fluid. Dough stage. Kernels filled with white paste. Dent stage milk line is close to the base of grain. The corn plant directs most of its energy and nutrient towards producing kernels on an ear. There is a heavy demand for water and nutrients. Severe moisture stress will give poor pollination and reduce kernel development. Stress in the early part of the period will affect kernel numbers while stress in the latter part will affect kernel weight. A poor seed set is usually the result of nutrient or water shortages that either delay silking or result in kernels aborting after pollination. This stage chiefly determines kernel size moisture stress will hasten maturity and reduce kernel fill through reduced photosynthesis and starch production, resulting in lower yields. Similarly, very favourable conditions of moisture and fertility will result in improved kernel fill and a better yield than expected. The last irrigation is important for final kernel size and is especially important for grit corn production. At 50 to 70 days after pollination the corn kernel will have reached its greatest dry weight and it is physiologically mature there will be no further response to additional water. R6 Physiological maturity. The appearance of a black layer at the base of the grain indicates physiological maturity 308 WATERpak a guide for irrigation management in cotton and grain farming systems

5 Figure WaterSched2 End of Season Field Summary report for a fully irrigated wheat crop at Dalby in 2009 End of Season Summary Field Summary Report Compiled By: Graham Harris graham.harris@deedi.qld.gov.au Farm: Wallon Park Plant Date: 1/09/2009 Location: Dalby Season: 2009/2010 Field Name: Wallon Park Length of Season: 147 days / 2093 GDD Field Size: 100 ha Irrigation Type: Surface 100% Crop: Late Maize Irrigation Trigger Deficit: 75 mm Water Summary Crop Summary mm ML/ha Expected Yield: 12 tonnes/ha Total Irrigation: Predicted Yield: 10.6 tonnes/ha Total Rainfall: Actual Yield: 10 tonnes/ha Total Losses: Accumulated ETp: 657 mm Starting Soil Water: Accumulated ETc: 597 mm Ending Soil Water: Economics Summary Soil Water Change: Price Per Unit: $250 / tonnes Total Water Input: Variable Costs: $1310 / ha Net Water Supply: Gross Margin: $1190 / ha Predicted Water Use Efficiency Actual Gross Margin Total Water Use Index TWUI 1.53 tonnes / ML 1.43 tonnes / ML $170 / ML Gross Production Water Use Index GPWUI 1.78 tonnes / ML 1.68 tonnes / ML $200 / ML Irrigation Water Use Index IWUI 2.66 tonnes / ML 2.5 tonnes / ML $298 / ML Crop Water Use Index CWUI kg / mm kg / mm $1.99 / mm Friday, 16 November 2012 End of Season Field Summary Page 1 of 1 Section 4: Irrigation management of grain crops 309

6 Agronomy To achieve high irrigated yields it is necessary to follow good agronomic practices. High yielding crops use water more efficiently than lower yielding crops. Nutrition Soil test regularly so that the most appropriate nutrition program can be drawn up based on your yield expectations. The three major nutrients required by corn are nitrogen (N), phosphorus (P) and potassium (K). At least 340 kg N/ha is needed to grow a 12.5 t/ha corn crop. This crop would also require 55 kg P/ha, 245 kg K/ha and 38 kg sulphur/ha. The corn plant rapidly takes up N, P and K beyond the 4 to 5 week (V8) period. Nitrogen is usually applied in a split application with 60-70% applied preplant and the remainder either water run or side dressed prior to tasseling (VT). Phosphorus and potassium are usually applied pre-planting or at planting as starter fertiliser. Variety Choice Corn hybrids are rated by maturity by comparing the moisture at harvest with a standard hybrid. This is called the Comparative Relative Maturity (CRM) and is commonly referred to as the days from planting to physiological maturity (black layer or R6). The actual days to maturity vary greatly with location, planting time and other environmental factors. The CRM maturity for Australian locations are summarised in Table Generally speaking, a longer maturity hybrid has a higher yield potential than a quick maturity hybrid (under ideal conditions). Advances in plant breeding have lessened this difference. There are many factors to consider in choosing a particular maturity hybrid. Quicker maturity hybrids may be chosen in response to: limited water availability or the desire to finish the crop before peak water requirements for other crops in January-February. Delayed spring planting with the aim of beating the summer heat before tasselling A late plant may be considered and there is a threat of an early frost Choose a range of hybrids that perform well in both favourable and less favourable conditions. 310 WATERpak a guide for irrigation management in cotton and grain farming systems

7 Table Guide to corn maturity plantings Location CRM Maturity (days) MIA, Lachlan and Macquarie Valleys Liverpool Plains and Northern NSW Further Reading Pacific Seeds - Cropping Yearbook Pioneer - Growth Potential: Corn growers Workshop Darling Downs and Burnett Central Queensland and Burnett North Queensland Row spacing For irrigated crops, rows of 76cm to 100cm are used, with most planters set up for 90cm rows. Under fully irrigated conditions the narrower rows have a slight yield advantage. Plant population Plant population is a critical decision in response to the hybrid chosen, water availability and planting time. Higher plant populations deplete available soil water at a faster rate than lower populations and irrigation frequency needs to increase accordingly. Higher populations also speed up maturity by up to 7 days. Planting Date Choice of planting date should be based on: Avoiding flowering during the expected peak temperature periods and working back to a suitable planting date for your hybrid of choice Plant when the soil temperature is at least 120C at 9am at a depth of 10cm for 3 to 4 consecutive days and is rising Avoiding seedling frosts on Spring planted corn that will damage the growing point or early frosts on late planted corn before physiological maturity (black layer) Section 4: Irrigation management of grain crops 311