Ian J. Rochester

Use of nitrification inhibitors to increase fertilizer nitrogen recovery and lint yield in irrigated cotton

This paper describes field experiments designed to evaluate the effectiveness of several nitrification inhibitors to prevent loss of fertilizer nitrogen (N) applied to cotton. The usefulness of nitrapyrin, acetylene (provided by wax-coated calcium carbide), phenylacetylene and 2-ethynylpyridine to prevent denitrification was evaluated by determining the recovery of N applied as15N labelled urea to a heavy clay soil in 1 m × 0.5 m microplots in north western N.S.W., Australia. In a second experiment, the effect of wax-coated calcium carbide on lint yield of cotton supplied with five N levels was determined on 12.5 m × 8 m plots at the same site.The15N balance study showed that in the absence of nitrification inhibitors only 57% of the applied N was recovered in the plants and soil at crop maturity. The recovery was increased (p < 0.05) to 70% by addition of phenylacetylene, to 74% by nitrapyrin, to 78% by coated calcium carbide and to 92% by 2-ethynylpyridine.In the larger scale field experiment, addition of the wax-coated calcium carbide significantly slowed the rate of NH4+ oxidation in the grey clay for approximately 8 weeks. Lint yield was increased (p < 0.05) by the addition of the inhibitor at all except the highest level of N addition. The inhibitor helped to conserve the indigenous N as well as the applied N.The research shows that the effectiveness of urea fertilizer for cotton grown on the heavy clay soils of N.S.W. can be markedly improved by using acetylenic compounds as nitrification inhibitors.

Phosphorus and potassium nutrition of cotton: interaction with sodium

Poor phosphorus (P) and potassium (K) nutrition limits the growth and yield of many cotton (Gossypium hirsutum L.) crops in Australia. The demand for nutrients from cotton crops has risen as yields have increased over the past 40 years, and some soils have become depleted in these nutrients. Cotton is commonly grown on sodic soils that are more prone to nutritional problems. A survey of thirty-one sites over four years in northern NSW, Australia included twelve sites that had sodic topsoil. However, available soil P and K at all sites were above established critical values for cotton crops. Soil sodicity was negatively correlated with available soil P and K, and positively with soil salinity and chloride. Cotton leaf P and K concentrations at flowering were negatively correlated with leaf sodium (Na) concentration. The cotton crops growing in sodic soils produced 20% less dry matter (3 weeks before crop defoliation) and crop P and K uptake was reduced by 23% and 25%, respectively, whereas Na uptake was 107% higher. High soil sodicity also reduced the uptake of micro-nutrients. Two field experiments in adjacent sodic and non-sodic areas on one farm showed a yield response to P fertiliser application at the non-sodic site only, but where soil P availability was above the accepted critical value. Application of K fertiliser did not increase crop K uptake or yield. The lower yield and poorer growth of irrigated cotton on sodic soils was related to higher Na uptake and lower P and K uptake, possibly due to restricted root growth in sodic soils.

Retention of cotton stubble enhances N fertilizer recovery and lint yield of irrigated cotton

Abstract Cotton ( Gossypium hirsutum L.) stubble is normally slashed and incorporated in Australian cotton production, but in recent years, some growers have raked and burned cotton stubble to facilitate tillage operations and irrigation management, and potentially to reduce the incidence of cotton diseases. An experiment was conducted over 3 years to investigate the effects of cotton stubble removal on lint yield and N fertilizer recovery of three consecutive cotton crops. After cotton-picking each year, the stubble was either retained or removed from the system and N fertilizer applied (0–200 kg N ha −1 ) to the same plots each year. About 1.4 Mg C ha −1 were removed in the cotton stubble each year, equivalent to about 5% of the C within the soil plow layer to 30 cm depth. Soil mineral N content prior to planting was slightly higher where stubble was removed, but N fertilizer recovery was reduced by 10%, meaned over the three seasons. Lint yield tended to decline with successive crops with stubble removal compared with stubble retention and in the third crop, yield was reduced by 10%. In a second field experiment, we demonstrated that the maceration of cotton stubble or its burial in contact with N fertilizer, compared with conventional stubble slashing and shallow incorporation, had no significant effect on soil mineral N content, crop N uptake, N fertilizer recovery or lint yield of cotton. It was concluded that stubble retention promotes a more biologically active soil system that is conducive to more efficient use of N fertilizer and maintains higher cotton yields.

Impact of waterlogging on the nutrition of cotton (Gossypium hirsutum L.) produced in sodic soils

Abstract. Sodicity in Vertosols used for agricultural production can adversely affect the growth and nutrition of cotton (Gossypium hirsutum L.) plants. Cotton produced in sodic soils has reduced dry matter and lint yield and can develop toxic plant tissue concentrations of sodium (Na) but limited tissue concentrations of phosphorus (P,) potassium (K), and micronutrients. Crops produced on sodic soils frequently suffer from aeration stress after an irrigation or rainfall event, and it was hypothesised that the adverse physical and/or chemical conditions of sodic soils may exacerbate the effects of waterlogging. We measured the impacts of sodicity on the growth, nutrition, and root recovery time of cotton during and after waterlogging in two experiments. In the first, cotton plants were subjected to a 7-day period of inundation in Grey Vertosols with a range of exchangeable sodium percentage (ESP) values from 2 to 25%; 32P was placed in the pots and its accumulation in the plant was used to indicate root activity and recovery after the waterlogging event. In a second experiment, agar was dissolved in nutrient solutions with a range of Na concentrations (9, 30, and 52 mm) matching soil solution Na concentrations in sodic soils, in order to simulate a waterlogging event. Following the waterlogging event, the solutions were labelled with 32P, in order to determine the effect of sodic soil solution chemistry on the rate of recovery of cotton root function after the event. Plant nutrient analysis was used to determine the effects of sodicity and waterlogging on cotton nutrition. In both experiments, waterlogging reduced root activity and reduced the uptake and transport of labelled P by the cotton plants, decreased plant P and K concentrations, and increased the plant Na concentrations. Sodicity exacerbated the effects of waterlogging on root function and cotton nutrition in the soil experiment but not in the nutrient solution experiment, suggesting that any contribution of waterlogging to the patterns of nutrient accumulation in cotton crops produced in sodic fields occurs due to soil physical factors rather than soil solution chemistry.

The effect of sodicity on cotton: Does soil chemistry or soil physical condition have the greater role?

Abstract. Soil sodicity is widespread in the cracking clays used for irrigated cotton (Gossypium hirsutum L.) production in Australia and worldwide and sometimes produces nutrient imbalances and poor plant growth. It is not known whether these problems are due primarily to soil physical or to soil chemical constraints. We investigated this question by growing cotton to maturity in a glasshouse in large samples of a Grey Vertosol in which the exchangeable sodium percentage (ESP) was adjusted to 2, 13, 19, or 24. A soil-stabilising agent, anionic polyacrylamide (PAM), was added to half the pots and stabilised soil aggregation at all ESPs. Comparison of the effect of ESP on cotton in the pots with and without PAM showed that, up to ESP of 19, the soil physical effects of sodicity were mainly responsible for poor cotton performance and its ability to accumulate potassium. At ESP >19, PAM amendment did not significantly improve lint yield, indicating that soil chemical constraints, high plant sodium concentrations (>0.2%), and marginal plant manganese concentrations limited plant performance. Further research into commercial methods of amelioration of poor physical condition is warranted rather than application of more fertiliser.

Nitrogen fertiliser requirements of high-yielding irrigated transgenic cotton

Abstract. Nitrogen (N) fertiliser is almost universally used in high-yielding irrigated cotton, but it is not used efficiently in many instances. Predicting the economic optimal amount of N fertiliser is difficult and often little N fertiliser is required where situations have provided access to N through excessive N fertiliser being applied to previous cotton crops, conditions promoting significant N mineralisation, or if legume rotation crops were grown. The economic optimum N fertiliser rate (Nopt – where the marginal cost of N fertiliser (at

Growth and phosphorus uptake of faba bean and cotton are related to Colwell-P concentrations in the subsoil of Vertosols

1.50 kg–1 N) equalled the return on cotton lint (at

Quantifying nitrous oxide emissions from the foliage of cotton, maize and soybean crops

2.20 kg–1) was determined in eight experiments conducted over 8 years; Nopt ranged from 0 to 248 kg N ha–1, lint yields ranged from 1.3 to 3.4 t ha–1, crop N uptake ranged from 96 to 321 kg N ha–1 and apparent N fertiliser recovery (calculated by dividing the difference in crop N uptake between N-fertilised and unfertilised plots by the N fertiliser applied) ranged from 20% to 98% of N applied. A positive response to N fertiliser application in lint yield was evident in 7 of the 8 years. Both lint yield and crop N uptake were positively correlated with pre-sowing soil nitrate concentration. Cotton that yielded 1.4 t lint ha–1 derived 78% of crop N from the soil, whereas at 3.4 t lint ha–1, 69% of crop N was derived from soil; this indicated the importance of N supplied from the soil and the relatively lesser reliance on the N fertiliser applied, even for very high-yielding cotton. A multiple regression model, using the parameters of pre-sowing soil nitrate, crop N uptake and lint yield, more accurately represented the data generated in this study in estimating the economic optimum N fertiliser rate (r2 = 0.80).

Nutrient uptake and export from an Australian cotton field

Abstract. Recent studies report low and variable phosphorus (P) fertiliser use efficiency (PUE) for cotton in the northern grains region (NGR) of eastern Australia. This may be due to cotton accessing P pools that are not currently tested for in the subsoil (10–30 cm) or variation in response to P source and placement strategy. Two glasshouse studies were used to investigate this, incorporating two soil P tests to assess readily and slowly available P pools (Colwell, and a dilute acid colloquially referred to as the BSES extractant), and five different P fertiliser placement strategies in the subsoil. Eighteen Vertosols were collected across southern to central Queensland in the NGR, and then used to grow faba bean (Vicia faba L.) and cotton (Gossypium hirsutum L.) sequentially in the same 28-L pot. Readily available P pools assessed by Colwell-P were of major importance for faba bean and cotton dry matter, as well as for tissue P concentrations. Cotton was less responsive to extractable subsoil P concentrations than faba bean, suggesting either greater internal PUE or improved ability to accumulate P under conditions of limited availability. We recommend that subsoil P fertilisation should occur before sowing faba bean to maximise PUE in a cotton–faba bean rotation. Faba bean and cotton both recovered more P when the subsoil was fertilised, but no individual P fertiliser placement strategy was superior. Phosphorus extracted using the BSES method was not correlated with faba bean or cotton dry matter or tissue P concentration over the single crop cycle. We also recommend that Colwell-P be measured in the topsoil and subsoil to understand the quantity of plant-available P in Vertosols of the NGR, and that further research is needed to describe the resupply of the readily available P pool from slowly available P pools during a single crop cycle.

Sequestering carbon in minimum-tilled clay soils used for irrigated cotton and grain production

Abstract. Nitrous oxide (N2O) is a potent greenhouse gas, contributing to global warming. Most of the N2O emitted from cropping systems is derived from the soil and is closely related to the use of nitrogen (N) fertiliser. However, several reports have shown that small, yet significant, portions of the N2O flux from cropping systems are emitted from the crop foliage. This research aimed to quantify N2O emissions from the foliage of field-grown cotton (Gossypium hirsutum L.), and included maize (Zea mays L.) and soybean (Glycine max L.) for comparison. We also aimed to identify differences in the timing of N2O emissions from foliage during the day and over an irrigation cycle. Individual plants were isolated from the soil, and the atmosphere surrounding the encapsulated plants was sampled over a 30-min period. Subplots that were previously fertilised with urea at 0, 80, 160, 240 and 320 kg N ha–1 and then sown to cotton were used to measure N2O flux from plants on three occasions. N2O flux from cotton foliage was also measured on five occasions during an 11-day irrigation cycle and at five times throughout one day. N2O flux from foliage accounted for a small but significant portion (13–17%) of the soil–crop N2O flux. N2O flux from foliage varied with plant species, and the time of day the flux was measured. N2O flux from cotton plants was closely related to soil water content. Importantly, the application of N fertiliser was not related to the N2O flux from cotton plants. The most plausible explanation of our results is that a proportion of the N2O that was evolved in the soil was transported through the plant via evapotranspiration, rather than being evolved within the plant. Studies that exclude N2O emissions from crop foliage will significantly underestimate the N2O flux from the system.