“It is possible to increase crop yields on sandy soils by 300 per cent. Practices such as applying chicken manure, strategic cultivation/spading/ripping, variety choice, seeding rate, applying adequate nitrogen and phosphorus, and in some cases lime all contributed to yield increases”.
So, reported Barry Haskins, agronomist and director of Ag Grow Agronomy and Research, at the recent Wagga Wagga GRDC update seminar. He detailed results from a GRDC research project he leads and involving many trials and collaborators throughout south west NSW, SA and Vic.
Sandy soils form more than 30 percent of the cropping and grazing landscape across central and southern inland NSW, parts of VIC and SA, Mr Haskins notes. These soils often produce lower crop yields than other soils and are acidic (pH CaCl 4 to 5, NSW mainly), highly erodible, carrying high weed numbers and often accommodate limited root growth which causes soil moisture to remain after harvest.
Light soils are usually those with more than 75 percent course sand and Cation Exchange Capacities (CEC) of less than 5mg/kg reports Mr Haskins. They are naturally low in fertility and store minimal plant available water (PAW), 60 to 80mm.
Constraints to rooting depth and water extraction include physical and chemical impediments, nutrient supply and biological cycling, water repellence, poor establishment, and movement of water and nutrients beyond the rooting zone Mr Haskins says. Farming system constraints include effective broadleaf rotations, crop choice and varietal performance, erosion, disease and weed risks.
Research sites include Griffith (NSW), Ouyen (VIC) and Lameroo (SA). Outcomes from the research so far indicate variety choice and seeding rate relationships are often different than for heavier soils. Strategic nutrition management, effect of manure, lime and cultivation and impact of herbicides and their residues are also important issues.
Varietal performance did not clearly relate to expected acid tolerance indicated from NVT trials on heavier soils. For example yields in a 2015 trial ranged from 1.0t/ha (Bellaroi) to more than 4.0t/ha (La Trobe, Compass). Suntop, Bolac, Spitfire, Gregory, Corack and Ventura all performed midrange (3.4 to 3.8t/ha).
Good gains occurred in good years from higher seed rate. For example yield from Suntop improved by 1.3t/ha by increasing seeding rate from 40 to 150kg/ha. In 2017, a dry year, higher seeding rates (> 60kg/ha) caused premature haying off with no significant yield difference between 20kg and 140kg/ha. Lime made little or no difference to varietal performance in a 2015 experiment.
Highest yields were from application of a at least 3.0t/ha chicken manure. Nitrogen and phosphorous were both important for high yields. Tissue testing for micronutrient imbalances followed by the application of foliar fertilisers (zinc, copper and molybdenum to correct imbalances did not increase yield.
A trial established in 2017 aimed to better understand the multi-season impact of deep cultivation with/without chicken litter and lime. Results from the first year, indicate little gain from the physical intervention (deep cultivation or deep ripping) during the dry season. The greater yield gains (2.7t/ha) compared to the control (non-cultivation) were associated with higher nitrogen inputs (100kg/ha) MAP fertiliser treatment (3.6t/ha), or chicken litter treatment (4t/ha). Subsequent seasons’ results will evaluate economic benefits of more costly amelioration approaches.
Glyphosate and AMPA residues can be phytotoxic on sensitive plant species. Wheat is relatively tolerant to glyphosate but legumes (especially lupin and soybean) are noted as more sensitive. Other ongoing research is exploring their possible toxicity, especially in sandy soils.
