Impact of Practice Change on Runoff Water Quality and Vegetable Yield—An On-Farm Case Study

Abstract

Abstract:Intensive agricultural practices in farming systems in eastern Australia have been identified as a contributor to the poor runoff water quality entering the Great Barrier Reef (GBR). A field investigation was carried out to measure the off-farm water quality and productivity in a coastal farming system in northeastern Australia. Two vegetable crops (capsicum and zucchini) were grown in summer 2010-2011 and winter 2011 respectively using four different management practices (Conventional-plastic mulch, bare inter-row conventional tillage and commercial fertilizer inputs; Improved-improved practice with plastic mulch, inter-row vegetative mulch, zonal tillage and reduced fertilizer rates; Trash mulch-improved practice with cane-trash or forage-sorghum mulch with reduced fertilizer rates, minimum or zero tillage; and Vegetable only-improved practice with Rhodes grass or forage-sorghum mulch, minimum or zero tillage, reduced fertilizer rates). Results suggest improved and trash mulch systems reduced sediment and nutrient loads by at least 50% compared to conventional systems. The residual nitrate nitrogen in soil accumulated at the end-of-break crop cycle was lost by deep drainage before the subsequent sugarcane crop could utilize it. These results suggest that future research into establishing the linkages between deep drainage, groundwater quality and lateral movement into adjacent streams is needed. The improvement in runoff water quality was accompanied by yield reductions of up to 55% in capsicum and 57% in zucchini under trash mulch systems, suggesting a commercially unacceptable trade-off between water quality and productivity for a practice change. The current study has shown that variations around improved practice (modified nutrient application strategies under plastic mulch, but with an inter-space mulch to minimize runoff and sediment loss) may be the most practical solution to improve water quality and maintain productivity. However, more work is required to optimize this approach and thus reduce the size of any potential productivity and profitability gap that would necessitate an expensive policy intervention to implement.

Productivity Benefits from Plastic Mulch in Vegetable Production Likely to Limit Adoption of Alternate Practices that Deliver Water Quality Benefits: An On-Farm Case Study

“…The residual nutrients left in the soil profile after the capsicum crop in the 'Conventional' system were much higher than in the 'Improved' system [11,21]. The yield gap of 5 t/ha between the 'Improved' and 'Conventional' systems with fertiliser applications based on a pre-planting soil test (e.g., 82 and 105 kg N/ha, respectively) decreased slightly to 4 t/ha when luxury fertiliser rates were applied (e.g., 161 kg N/ha).…”

“…While the plastic mulch provided few consistent benefits in raising soil temperature during the summer, the very heavy rainfall that occurred from late December to January was likely to result in significant leaching of nutrients in the open systems [11], while the systems covered with plastic mulch would have been much less affected. This was consistent with the observation of poor crop nutrient status in the trash mulch systems, and led to the conclusion that the main difference in crop performance between the management systems was related to the nutrient management inputs.…”

“…Yields in the 'Improved' system were only about 80% of the yields of the 'Conventional' system, while yields in the 'Trash mulch' and 'Vegetable only' systems were only 43% and 49% of the 'Conventional' system, respectively, for the management systems with soil testbased nutrient applications. A pumpkin crop following the zucchini crop in the 'Vegetable only' system (data not shown) also yielded only 39% of the district average productivity [11]. Gross margin …”

“…The entire field was subdivided into five management units 9 m wide, with four of these units sown to vegetable crops, and these contiguous management units were further split into two blocks draining in opposite directions from the highest elevation near mid field. The smaller 120 m blocks (where runoff flumes and water quality samplers were installed [11]) were treated with the contrasting fertiliser application strategies, as shown in Table 1, throughout the monitoring period, while the 160 m blocks received the same contrasting applications in the initial capsicum crop but a common, high application (HF) rate in the following zucchini crop (see Section 2.2.1). Soil temperature (5 cm depth) was monitored during the capsicum and zucchini crop season using Tinytag plus2 (Gemini data loggers (UK) Ltd, Chichester, West Sussex PO198UJ, England), with data presented in Figures S1 and S2 (supplementary data).…”

Organic and non-organic mulches – impact on environmental conditions, yield, and quality of Cucurbitaceae

“…Despite the many advantages of using such materials, they are not neutral to the soil environment (Steinmetz et al, 2016). Compared to conventional crops, cropping systems making use of cover plants, based on the limitation of cultivation practices and mineral fertilization, can be associated with a significant drop in yield -by as much as 57% in zucchini cultivation (Nachimuthu et al, 2017).…”