Sieglinde Snapp and Carol Shennan
Tomato Fruit quality can be improved by the use of moderately saline irrigation water. However, decreased fruit yields may occur if the saline treatment is initiated early in plant development or the salt concentration is high. Another concern with the use of saline irrigation water is increased plant susceptibility to disease. Two processing tomato cultivars were grown under low salt (ECa=1.1 ds/m), medium salt (ECa=2.8 ds/m) and high salt (ECa=4.6 ds/m) regimes, and in the presence and absence of Phytophthora parasitica, the casual agent of Phytophthora root rot. Salinity increased Phytophthora root rot severity in UC82B, the susceptible cultivar, but had a limited effect on CX8303, a cultivar known to have a measure of resistance to Phytophthora root rot. Fruit acidity and percent total soluble solids were enhanced in both cultivars by increasing salinity. Infection by P. parasitica increased acidity and soluble solids in UC82B fruit grown under high salt. Sodium and chloride concentrations in tomato fruit increased in a manner proportionate to the salt treatment applied; however, in the absence of disease, fruit Na+ and Cllevels were markedly lower compared to other tissues in the plant, The presence of salt-enhanced Phytophthora root rot in UC82B increased fruit Na+ concentration by almost 100%. Fruit Ca2+ and K+ levels, in contrast, declined moderately with increasing salinity and were not affected by disease.
Carol Shennan, Stephen R. Grattan, Don May, and Carol J. Hillhouse
Reuse of saline drainage water for crop irrigation has been proposed as one strategy to reduce the drainage volume requiring disposal in California. A 6 y study to assess the feasibility of cyclic saline drainage reuse in a processing tomato/ cotton /cotton rotation was conducted. Treatments were: 1. fresh water applied throughout, 2. saline water applied after 1st flower to tomatoes, 3. saline water applied to tomato and the next cotton crop. Saline water generally improved tomato fruit quality, but did not reduce yields during the first 4 years. In year 6, yields were reduced 17% (n.s.) and 30% (p<0.05) in treatments 2 and 3 respectively, relative to the control. Monitoring of the root zone showed that boron has accumulated over time in saline treatments and may be limiting crop production more than soil salinity. Selenium was readily leached by periodic fresh water use and did not accumulate to levels of concern in tomato tissues. Other work has shown that salinity can enhance tomato susceptibility to root rot which may limit this practice in some areas. However, the data show that high value crops like tomato can be incorporated into saline reuse schemes if managed appropriately.
Laurie E. Drinkwater, Deborah K. Letourneau, Fekede Workneh, Marita Cantwell, Ariena H.C. van Bruggen, and Carol Shennan
Twenty commercial tomato production systems were compared in a multidisciplinary on farm study. The aim was to determine if organic (ORG) and conventional (CNV) systems differed in terms of agronomic criteria or indicators of underlying ecological characteristics. Field level measures of inputs, yields, fruit quality, arthropod abundance and management operations were made. Also, multiple samples within each field were taken to measure soil chemical and physical properties, root pathogen populations, disease incidence, and pest damage levels for multivariate analysis. Management effects on agronomic criteria (yield, fruit quality, pest damage) were small, whereas differences in soil N pools, microbial activity, pathogen populations and arthropod communities between ORG and CNV sites were sufficiently robust to be distinguished from site to site variation. Relationships between management, crop productivity and fruit quality will be discussed.
Joji Muramoto, Richard F. Smith, Carol Shennan, Karen M. Klonsky, James Leap, Miriam Silva Ruiz, and Stephen R. Gliessman
Legume/cereal mixed winter cover crops are commonly used by organic growers on the central coast of California, but they are unable to provide sufficient nitrogen (N) for a high N-demanding vegetable crop such as broccoli and supplemental fertilizer application may be necessary. The goals of this project were to evaluate the contribution of N from a mixed legume/cereal cover crop (CC) and feather meal and blood meal as organic fertilizers (OF) to an organic broccoli crop and to evaluate economic benefits of CC and OF to the subsequent organic broccoli crop. Trials were conducted at two sites (A and B) with different management histories. Cover crops were grown over the winter and incorporated into the soil in the spring and subsequently broccoli [Brassica oleracea L. (Italica group)] was grown in 2006 at both sites and in 2007 at B only. Cover crop and no CC treatments were grown with supplemental organic fertilizers at four fertility levels (0, 84, 168, and 252 kg N/ha of OF) with four replicates. Generally broccoli head yields at A (14.9 to 26.3 Mg·ha−1) were higher than at B (0.7 to 17.4 Mg·ha−1 in 2006 and 5.5 to 17.9 Mg·ha−1 in 2007). Yield and aboveground biomass N were significantly increased by OF at rates up to 168 kg N/ha at A and to 252 kg N/ha at B and by CC in 2006 at both sites but not in 2007 at B. Although N content of the CC was similarly low at A (2006) and at B (2007), immobilization of soil mineral N occurred only at B. This suggests that the addition of a low N content CC was offset by high N mineralization from the soil at A with a long organic management history (greater than 33 years). Supplemental fertilizer applications may be necessary to achieve optimal yields, but the amount needed can be reduced by cover cropping in fields with a long history of cover crop-based organic management (A) or when cover crop N content is sufficiently high to prevent immobilization (B, 2006). Soil NO3-N patterns suggest a pre-side dress nitrate test may also be useful for N management in organic broccoli. Use of cover crops increased net return above harvest and fertility costs when the yield reduction by N immobilization did not take place. However, the net return increase by the use of cover crops tended to diminish as the rate of OF application increased.