Field studies on some effects of chloride fertilizers on the growth, yield and nutrient status of fodder beet (Beta vulgaris L.) and on some soil properties of two New Zealand soils

Abstract

Field trials using the 'Trestel' fodder beet variety were conducted at two sites on the Canterbury Plains: Templeton Research Station and Lincoln College mixed cropping farm, on Templeton silt loam (Dystric Ustochrept) and Wakanui silt loam (Aquic Eutrochrept), respectively. At the Templeton site, two field trials (Trials 1 and 3) were conducted, together with an additional trial (Trial 4) to investigate the residual effects; while at the Lincoln site, one trial (Trial 2) was conducted.

A randomized complete block design was used in Trial 1 (Templeton 1981/82) and Trial 2 (Wakanui 1981/82) with four replicates and 11 fertilizer treatments consisting of: (F₀) - control; (F₁) - 357 kg (NH₄)₂SO₄/ha alone; (F₂)- 295 kg NaCl/ha + F₁; (F₃)- 590 kg NaCl/ha + F₁ ; (F₄) – 885 kg NaCl/ha + F₁; (F₅) - 1180 kg NaCl/ha + F₁; (F₆) – 359 kg Na₂S0₄/ha + F₁; (F₇) - 720 kg Na₂S0₄/ha + F₁; (F₈) - 1078 kg Na₂SO₄/ha + F₁; (F₉) - 758 kg KCl/ha + F₁; and (F₁₀) - 878 kg K₂SO₄/ha + F₁. In Trial 3 (Templeton 1982/83), only seven of the 11 fertilizer treatments of Trial 1 (i.e. F₀, F₁, F₃, F₄, F₇, F₈ and F₉) were used. The experimental block used for Trial 1 (Templeton 1981/82) was divided into two blocks longitudinally with half of the block used for Trial 3 and the other half for Trial 4 (Residual Effects Study). Trials 1, 2 and 3 examined effects of Cl and non-Cl fertilizers, and increasing rates of NaCl (0, 295, 590, 885 and 1180 kg/hal on the growth and yield of fodder beet; and the influence of Cl fertilizers (NaCl and KCl) on the nutrient concentration (%) and uptake (N, P, K, Na, Ca, Mg, Cl, S) and the ionic composition and cation-anion balance of fodder beet. In addition, the periodic changes of five soil depths (0-10, 10-20, 20-40, 40-60, 60-80+ cm) of some soil properties (pH; total soluble salts; soluble Cl; exchangeable Na, K, Ca, Mg; bulk density) and population changes of soil nematode were measured. Trial 4 examined the residual effects of a single application of Cl fertilizers on the yield and 'apparent' plant uptakes of Na, K, and Cl by the beet crop.

Nutrient inputs from the rainfall, particularly Cl, K and Na were determined using rain collectors during the entire cropping period at the Templeton (1981/82 and 1982/83) and Lincoln (1981/82) sites. Irrigation water samples from both sites were also collected and analyzed for the same nutrient inputs as in the rainfall.

The application of 360 kg Cl/ha, either as 590 kg NaCl or 758 kg KCl/ha significantly increased fresh and dry tops weights, fresh and dry root weights of fodder beet in both Templeton soil and Wakanui soil at various growth stages during the 1981/82 cropping.

Although no response to N application was observed during the first cropping in either soil, the second beet crop in the Templeton soil (cropping 1982/83) responded positively to N in tops, root and sugar yields.

At 360 kg Cl/ha, both NaCl (590 kg) or KCl (758 kg/ha) were effective sources of Cl in increasing the yields of fresh roots, dry roots and fresh sugar. Moreover, with the increasing rate of NaCl (0-1180 kg/ha), yields of fresh roots and fresh sugar trends were linear in the Templeton soil, and quadratic (highest yields at 295 kg NaCl/ha) in the Wakanui soil. This difference in trends between soils was explained on the basis of differences in exchangeable Na (Templeton soil: 0.09-0.13 meq/100 g; Wakanui soil: 0.21-0.29 meq/100 g soil) and Cl inputs in irrigation water (Templeton: 4 kg Cl/ha; Wakanui: 33 kg Cl/ha) as Cl inputs from rainfall were similar (Templeton: 37 kg Cl/ha; Wakanui: 41 kg Cl/ha).

The application of Cl (from NaCl and KCl) was found to enhance the absorption of K from the soil by the beet crop, resulting in high K concentration (%) in the plant, particularly in the storage roots. In both soils, 590 kg NaCl/ha (360 kg Cl, 230 kg Na/ha) applied gave similar patterns of uptake of tops Cl and K, and root Cl, Na and K during the cropping period.

In both soils, total (tops + roots) uptakes of K, Cl and Na were all positively correlated (P≤ 0.01) with the economic yield indices (fresh roots, dry roots, and fresh sugar). Multiple-regression analyses showed that in the Templeton soil, total K uptake was the main nutritional factor which determined yields of fresh and dry roots; while in the Wakanui soil, the total Cl uptake and total K + total Cl uptakes determined high fresh root and dry root yields, respectively . But for increased sugar yields, high total Cl uptake was required in both soils during the first cropping. The best predicting equation obtained for fresh sugar yield were: Y = 993.54 + 54.5X for Templeton soil; and Y = 477.1 + 447X for Wakanui soil, where Y = fresh sugar yield (g/10 plants), X = total Cl uptake (g/10 plants).

The fodder beet was found to maintain the constancy of the sum of cations (SC) and cation-anion balance (C-A) within the range of 0-1180 kg NaCl/ha applied, but not the sum of anions (SA) which linearly increased with the increasing rates of NaCl (0-1180 kg/ha) applied. The plant ratio of the sum of cations and the sum of anions (RCA) showed a more consistent and reliable index for yield than its C-A balance. In both soils, fodder beet with lower RCA was apparently associated with higher fresh and dry root yields, and fresh sugar production.

During the entire cropping period (including the final harvest), and high concentrations of Cl, Na and K resulting from NaCl and KCl applications, were found in the topsoil (0-20 cm) of both soils. This restricted movement was due to the limited rainfall (240-294 mm), excessive evapotranspiration (811-813 mm), soil exchange reactions, and nutrient recycling. The single application of increasing rates of NaCl (0-1180 kg/ha) did not affect soil properties such' as pH, exchangeable K, Ca, Mg and bulk density of Templeton and Wakanui soils.

The application of 360 kg Cl/ha (590 kg NaCl, 758 kg KCl) produced an apparent nematicidal effect as revealed by the reduction in population densities of free-living nematodes and the parasitic Paratylenchus projectus.

No residual response to the single application of Cl fertilizers (NaCl and KCl) in the Templeton soil (cropping 1981/82) was obtained. This was mainly attributed to the high levels of exchangeable Na (0.46 - 0.61 meq/100 g) and K (0.79 - 1.04 meq/100 g soil) present in this soil prior to cropping, resulting from the nutrient recycling by the previous crop.

Practical implications of the results obtained in the study with respect to the applications of Cl fertilizers on the beet crop were discussed.